A HANDBOOK
OF
SYSTEMATIC BOTANY

BY

DR. E. WARMING

Professor of Botany in the University of Copenhagen

With a Revision of the Fungi by
DR. E. KNOBLAUCH,
Karlsruhe

Translated and Edited by
M. C. POTTER, M.A. F.L.S.

Professor of Botany in the University of Durham
College of Science, Newcastle-upon-Tyne
Author of “An Elementary Text-book of Agricultural Botany”

WITH 610 ILLUSTRATIONS

London

SWAN SONNENSCHEIN & CO

NEW YORK: MACMILLAN & CO

1895

Butler & Tanner,
The Selwood Printing Works,
Frome, and London.

PREFACE.

The present translation of Dr. E. Warming’s Haandbog i den Systematiske Botanik is taken from the text of the 3rd Danish Edition (1892), and from Dr. Knoblauch’s German Edition (1890), and the book has been further enriched by numerous additional notes which have been kindly sent to me by the author. Dr. Warming’s work has long been recognised as an original and important contribution to Systematic Botanical Literature, and I have only to regret that the pressure of other scientific duties has delayed its presentation to English readers. Dr. Warming desires me to record his high appreciation of the careful translation of Dr. Knoblauch, and his obligation to him for a number of corrections and improvements of which he has made use in the 3rd Danish Edition. In a few instances I have made slight additions to the text; these, however, appear as footnotes, or are enclosed in square brackets.

In the present Edition the Thallophytes have been revised and rearranged from notes supplied to me by Dr. Knoblauch, to whom I am indebted for the Classification of the Fungi, according to the more recent investigations of Brefeld. The Bacteria have been revised by Dr. Migula, the Florideæ rearranged after Schmitz, and the Taphrinaceæ after Sadebeck. The main body of the text of the Algæ and Fungi remains as it was originally written by Dr. Wille and Dr. Rostrup in the Danish Edition, though in many places considerable alterations and additions have been made. For the sake of comparison a tabular key to the Classification adopted in the Danish Edition is given in the Appendix.

In the Angiosperms I have retained the sequence of orders in the Danish original, and have not rearranged them according to the systems more familiar to English students. In any rearrangement much of the significance of Dr. Warming’s valuable and original observations would have been lost, and also from a teacher’s point of view I have found this system of great value. Although at present it may not be completely satisfactory, yet as an attempt to explain the mutual relationships, development and retrogression of many of the orders, it may be considered to have a distinct advantage over the more artificial systems founded upon Jussieu’s Divisions of Polypetalæ, Gamopetalæ, and Apetalæ.

With reference to the principles of the systematic arrangement adopted, I may here insert the following brief communication from the author (dated March, 1890), which he has requested me to quote from the preface of Dr. Knoblauch’s edition:—“Each form which, on comparative morphological considerations, is clearly less simple, or can be shown to have arisen by reduction or through abortion of another type having the same fundamental structure, or in which a further differentiation and division of labour is found, will be regarded as younger, and as far as possible, and so far as other considerations will admit, will be reviewed later than the ‘simpler,’ more complete, or richer forms. For instance, to serve as an illustration: Epigyny and Perigyny are less simple than Hypogny; the Epigynous Sympetalæ, Choripetalæ, Monocotyledones are, therefore, treated last, the Hydrocharitaceæ are considered last under the Helobieæ, etc. Zygomorphy is younger than Actinomorphy; the Scitamineæ and Gynandræ therefore follow after the Liliifloræ, the Scrophulariaceæ after the Solanaceæ, Linaria after Verbascum, etc. Forms with united leaves indicate younger types than those with free leaves; hence the Sympetalæ come after the Choripetalæ, the Sileneæ after the Alsineæ, the Malcaceæ after the Sterculiaceæ and Tiliaceæ, etc.

“Acyclic (spiral-leaved) flowers are older than cyclic (verticillate-leaved) with a definite number, comparing, of course, only those with the same fundamental structure. The Veronica-type must be considered as younger, for example, than Digitalis and Antirrhinum, these again as younger than Scrophularia; Verbascum, on the contrary, is the least reduced, and therefore considered as the oldest form. Similarly the one-seeded, nut-fruited Ranunculaceæ are considered as a later type (with evident abortion) than the many-seeded, folicular forms of the Order; the Paronychieæ and Chenopodiaceæ as reduced forms of the Alsineæ type; and the occurrence of few seeds in an ovary as generally arising through reduction of the many-seeded forms. The Cyperaceæ are regarded as a form derived from the Juncaceæ through reduction, and associated with this, as is so often the case, there is a complication of the inflorescence; the Dipsacaceæ are again regarded as a form proceeding from the Valerianaceæ by a similar reduction, and these in their turn as an offshoot from the Caprifoliaceæ, etc. Of course these principles of systematic arrangement could only be applied very generally; for teaching purposes they have often required modification.”

In preparing the translation considerable difficulty has been experienced in finding a satisfactory rendering of several terms which have no exact equivalent in English. I may here especially mention the term Vorblatt (Forblad) which I have translated by the term bracteole, when it clearly applied to the first leaf (or leaves) on a pedicel; but in discussing questions of general morphology a term was much needed to include both vegetative and floral shoots, and for this I have employed the term “Fore-leaf.” Also, the term “Floral-leaf” has been adopted as an equivalent of “Hochblatt,” and the term “bract” has been limited to a leaf subtending a flower. I have followed Dr. E. L. Mark in translating the word “Anlage” by “Fundament.”

At the end of the book will be found a short appendix giving an outline of some of the earlier systems of Classification, with a more complete account of that of Hooker and Bentham.

In a book of this character it is almost impossible to avoid some errors, but it is hoped that these will be comparatively few. In correcting the proof-sheets I have received invaluable assistance from Dr. Warming and Dr. Knoblauch, who have kindly read through every sheet, and to whom I am greatly indebted for many criticisms and suggestions. I have also to thank Mr. I. H. Burkill for his kind assistance in looking over the proofs of the Monocotyledons and Dicotyledons, and Mr. Harold Wager for kindly reading through the proofs of the Algæ and Fungi. My thanks are also especially due to Mr. E. L. Danielsen, and I wish to take this opportunity of acknowledging the very considerable help which I have received from him in translating from the Original Danish.

M. C. POTTER.

January, 1895.

TABLE OF CONTENTS.

BEING THE SYSTEM OF CLASSIFICATION ADOPTED IN THE PRESENT VOLUME.

(The Algæ and Fungi rearranged in co-operation with Dr. E. Knoblauch, the other Divisions as in the 3rd Danish Edition.)

CORRIGENDA.

• Page 9, line 12 from top, for Hydrodicton read Hydrodictyon.
• „  14, lines 1 and 2 from top, for as in the preceding case read in this case.
• „  14, „  2 and 15 from top, for zygote read oospore.
• „  88, line 15 from bottom, for Periphyses read periphyses.
• „  124, „  7 „   „  for Chæromyces read Choiromyces.
• „  142, „  2 „   „  and in Fig. 137, for Bœomyces read Bæomyces.
• „  152, „  2 „  top, for Pirus read Pyrus.
• „  152, „  5 „   „  for Crategus read Cratægus.
• „  216, Fig. 215, for Salvina read Salvinia.
• „  306, line 6 from top, for Pista read Pistia.
• „  316, „  26 „   „  after Dracæna insert a comma.
• „  337, „  13 „   „  for end read beginning.
• „  483, „  11 „  bottom, for Lagerstrœmia read Lagerstrœmeria.

For ä, ö and ü read æ, œ and ue throughout.

The following are not officinal in the British Pharmacopœia:—page 316, Dracæna (Dragon’s-blood), Smilax glabra; p. 321, “Orris-root”; p. 326, species of Curcuma, Alpinia officinarum; p. 333, Orchis-species (“Salep”). On page [296], par. 4, only Pearl Barley is offic. in the Brit. Phar.

CLASSIFICATION OF THE VEGETABLE KINGDOM.

The Vegetable Kingdom is arranged in 5 Divisions.

Division I.—Thallophyta, Stemless Plants, or those which are composed of a “thallus,” i.e. organs of nourishment which are not differentiated into root (in the sense in which this term is used among the higher plants), stem, or leaf. Vascular bundles are wanting. Conjugation and fertilisation in various ways; among most of the Fungi only vegetative multiplication.

In contradistinction to the Thallophytes all other plants are called “Stem-plants” (“Cormophyta”), because their shoots are leaf-bearing stems. The name Thallophyta (Stemless-plants) is to some extent unsuitable, since many of the higher Algæ are differentiated into stem and leaf.

The Thallophytes are again separated into 3 sub-divisions, namely:

• Sub-Division A.—Myxomycetes, Slime-Fungi, with only 1 class.
• Sub-Division B.—Algæ, with 10 classes:
• Class 1. Syngeneticæ.
• „ 2. Dinoflagellata, Peridinea.
• „ 3. Diatomeæ, Diatoms.
• „ 4. Schizophyta, Fission Algæ.
• „ 5. Conjugatæ.
• „ 6. Chlorophyceæ, Green Algæ.
• „ 7. Characeæ, Stone-worts.
• „ 8. Phæophyceæ, Brown Algæ.
• „ 9. Dictyotales.
• „ 10. Rhodophyceæ, Red Algæ.
• Sub-Division C.—Fungi, with 3 classes:
• Class 1. Phycomycetes.
• „ 2. Mesomycetes.
• „ 3. Mycomycetes, Higher Fungi.

Division II.—Bryophyta or Muscineæ, Mosses. These have leaf-bearing shoots, but neither true roots nor vascular bundles. The lowest Mosses have, however, a thallus. Fertilisation is accomplished by means of self-motile, spirally coiled spermatozoids, through the agency of water. From the fertilised oosphere a “fruit-body” (capsule) with unicellular organs of reproduction (spores) is produced. The spore on germination gives rise to the vegetative system, which bears the organs of sexual reproduction; and this system is divided into two stages—the protonema, and the leaf-bearing plant produced on it.

Alternation of generations:

• I. The protonema and the entire nutritive system which bears the organs of sexual reproduction.
• II. The capsule-like sporangium, with spores.
• 2 Classes: 1. Hepaticæ, Liverworts.
• 2. Musci, Leafy Mosses.

Division III.—Pteridophyta or Vascular Cryptogams, Fern-like Plants having leaf-bearing shoots, true roots, and vascular bundles with tracheides and sieve-tubes. Fertilisation as in the Mosses. From the fertilised oosphere the leaf-bearing shoot arises, which bears on its leaves the reproductive organs, the spores, in capsule-like sporangia. From the germination of the spore a small prothallium is formed, which bears the sexual reproductive organs.

Alternation of generations:

• I. Prothallium with organs of sexual reproduction.
• II. Leaf-bearing shoot with capsule-like sporangia.
• 3 Classes: 1. Filicinæ, True Ferns.
• 2. Equisetinæ, Horsetails.
• 3. Lycopodinæ, Club-mosses.

Division IV.—Gymnospermæ. The vegetative organs are in the main similar to those in the 3rd Division; special shoots are modified into flowers for the service of reproduction. From the oosphere, which is fertilised by means of the pollen-tube, the leaf-bearing plant is derived; this passes the first period of its life as an embryo in the seed, and continues its development when the germination of the seed takes place. The organs corresponding to the spores of the two preceding Divisions, are called respectively the pollen-grain and embryo-sac. The pollen-grains are multicellular; i.e. they contain an indistinct prothallium. In the embryo-sac a prothallium, rich in reserve material (endosperm), with female organs of reproduction, is developed BEFORE FERTILISATION. The pollen-grains are carried by means of the wind to the ovules; these enclose the embryo-sac, and are situated on the open fruit-leaf (carpel), which has no stigma.

Alternation of generations:

• I. Prothallium = Endosperm in ovule.
• II. Leaf-bearing plant, with flowers which produce the pollen-sac and ovule.
• 3 Classes: 1. Cycadeæ.
• 2. Coniferæ.
• 3. Gnetaceæ.

Division V.—Angiospermæ. The members of this group are very similar to those of Division IV. The ovules are, however, encased in closed fruit-leaves (ovary), which have a special portion (stigma) adapted for the reception and germination of the pollen-grains. The pollen-grains are bicellular, but with only a membrane separating the two nuclei; they are carried to the stigma by animals (chiefly insects), by the wind, or by some other means. Endosperm is not formed till AFTER FERTILISATION. Alternation of generations in the main as in the Gymnosperms, but less distinct; while the sexual generation, the prothallium, with the organs of fertilisation, is also strongly reduced.

• 2 Classes:[1] 1. Monocotyledones. Embryo with one seed-leaf.
• 2. Dicotyledones. Embryo with two seed-leaves.

For a long time the vegetable kingdom has been divided into. Cryptogams (so called because their organs of reproduction remained for some time undiscovered), and Phanerogams or Flowering-plants which have evident sexual organs.

The first three divisions belong to the Cryptogams, and the third and fourth divisions to the Phanerogams. This arrangement has no systematic value, but is very convenient in many ways.

The Cryptogams are also known as Spore-plants, since they multiply by unicellular organs (spores), and the Phanerogams in contradistinction are called Seed-plants (Spermaphyta), since they multiply by seeds, multicellular bodies, the most important part of which is the embryo (a plant in its infancy). Mosses, Ferns, and Gymnosperms are together known as Archegoniatæ, since they possess in common a female organ of distinct structure, the Archegonium.

DIVISION I.
THALLOPHYTA.

The thallus in the simplest forms is unicellular; in the majority, however, it is built up of many cells, which in a few instances are exactly similar; but generally there is a division of labour, so that certain cells undertake certain functions and are constructed accordingly, while others have different work and corresponding structure. Vessels or similar high anatomical structures are seldom formed, and the markings on the cell-wall are with few exceptions very simple. The Myxomycetes occupy quite an isolated position; their organs of nourishment are naked masses of protoplasm (plasmodia).

As regards the external form, the thallus may be entirely without special prominences (such as branches, members), but when such are present they are all essentially alike in their origin and growth, that is, disregarding the hair-structures which may be developed. A shoot of a Seaweed or of a Lichen, etc., is essentially the same as any other part of the plant; only among the highest Algæ (Characeæ, certain Siphoneæ, Sargassum, and certain Red Seaweeds) do we find the same differences between the various external organs of the plant body as between stem and leaf, so that they must be distinguished by these names.

Roots of the same structure and development as in the Seed-plants are not found, but organs of attachment (rhizoids and haptera) serve partly the biological functions of the root.

Systematic division of the Thallophytes. To the Thallophytes belong three sub-divisions—Slime-Fungi, Algæ, and Fungi. Formerly the Thallophytes were divided into Algæ, Fungi, and Lichens. But this last group must be placed among the Fungi, since they are really Fungi, which live symbiotically with Algæ. The Slime-Fungi must be separated from the true Fungi as a distinct subdivision. The Algæ possess a colouring substance, which is generally green, brown, or red, and by means of which they are able to build up organic compounds from carbonic acid and water. The Bacteria, especially, form an exception to the Algæ in this respect; like the Fungi and Slime-Fungi they have as a rule no such colouring material, but must have organic carbonaceous food; these plants form no starch, and need no light for their vegetation (most Fungi require light for fructification). The Myxomycetes, Bacteria, and Fungi derive their nourishment either as saprophytes from dead animal or vegetable matter, or as parasites from living animals or plants (hosts), in which they very often cause disease.

A remark, however, must be made with regard to this division. Among the higher plants so much stress is not laid upon the biological relations as to divide them into “green” and “non-green”; Cuscuta (Dodder), a parasite, is placed among the Convolvulaceæ, Neottia and Corallorhiza, saprophytes, belong to the Orchidacere, although they live like Fungi, yet their relations live as Algæ. In the same manner there are some colourless parasitic or saprophytic forms among the Algæ, and stress must be laid upon the fact that not only the Blue-green Algæ, but also the Bacteria, which cannot assimilate carbonic-acid, belong to the Algæ group, Schizophyceæ. The reason for this is that systematic classifications must be based upon the relationship of form, development, and reproduction, and from this point of view we must regard the Bacteria as being the nearer relatives of the Blue-green Algæ. All the Thallophytes, which are designated Fungi (when the entire group of Slime-Fungi is left out), form in some measure a connected series of development which only in the lower forms (Phycomycetes) is related to the Algæ, and probably through them has taken its origin from the Algæ; the higher Fungi have then developed independently from this beginning. The distinction of colour referred to is therefore not the only one which separates the Algæ from the Fungi, but it is almost the only characteristic mark by which we can at once distinguish the two great sub-divisions of the Thallophytes.

The first forms of life on earth were probably “Protistæ,” which had assimilating colour material, or in other words, they were Algæ because they could assimilate purely inorganic food substances, and there are some among these which belong to the simplest forms of all plants. Fungi and Slime-Fungi must have appeared later, because they are dependent on other plants which assimilate carbon.[2]

Sub-Division I.—MYXOMYCETES, SLIME-FUNGI.

The Slime-Fungi occupy quite an isolated position in the Vegetable Kingdom, and are perhaps the most nearly related to the group of Rhizopods in the Animal Kingdom. They live in and on organic remains, especially rotten wood or leaves, etc., on the surface of which their sporangia may be found.

They are organisms without chlorophyll, and in their vegetative condition are masses of protoplasm without cell-wall (plasmodia). They multiply by means of spores, which in the true Slime-Fungi[3] are produced in sporangia, but in some others[4] free. The spores are round cells (Fig. [1] a) which in all the true Slime-Fungi are surrounded by a cell-wall. The wall bursts on germination, and the contents float out in the water which is necessary for germination. They move about with swimming and hopping motions like swarmspores (e, f), having a cilia at the front end and provided with a cell-nucleus and a pulsating vacuole. Later on they become a little less active, and creep about more slowly, while they continue to alter their form, shooting out arms in various places and drawing them in again (g, h, i, k, l, m); in this stage they are called Myxamœbæ.

Fig. 1.—a-l Development of “Fuligo” from spore to Myxamœba; a-m are magnified 300 times; m is a Myxamœba of Lycogala epidendron; l´ three Myxamœbæ of Physarum album about to unite; o, a small portion of plasmodium, magnified 90 times.

Fig. 2.—The plasmodium (a) of Stemonitis fusca, commencing to form into sporangia (b); drawn on July 9. The dark-brown sporangia were completely formed by the next morning; c-e shows the development of their external form.

Fig. 3.—Four sporangia of Stemonitis fusca, fixed on a branch. a The plasmodium.

Fig. 4.—Sporangium of Arcyria incarnata. B closed; C open; p wall of sporangium; cp capilitium.

The Myxamœba grows whilst taking up nourishment from the material in which it lives, and multiplies by division. At a later stage a larger or smaller number of Myxamœbæ may be seen to coalesce and form large masses of protoplasm, plasmodia, which in the “Flowers of Tan” may attain the size of the palm of a hand, or even larger, but in most others are smaller. The plasmodia are independent, cream-like masses of protoplasm, often containing grains of carbonate of lime and colouring matter (the latter yellow in the Flowers of Tan). They creep about in the decaying matter in which they live, by means of amœboid movements, internal streamings of the protoplasm continually taking place; finally they creep out to the surface, and very often attach themselves to other objects, such as Mosses, and form sporangia (Fig. [2]). These are stalked or sessile and are generally cylindrical (Fig. [3]), spherical or pear-shaped (Fig. [4]); they rarely attain a larger size than that of a pin’s head, and are red, brown, white, blue, yellow, etc., with a very delicate wall. In some genera may be found a “Capillitium” (Fig. [4] cp), or network of branched fine strands between the spores. Flowers of Tan (Fuligo septica) has a fruit-body composed of many sporangia (an Æthalium), which has the appearance of flat, irregular, brown cakes, inside the fragile external layer of which a loose powder, the spores, is found. It generally occurs on heaps of tanners’ bark, and appears sometimes in hot-beds in which that material is used, and is destructive by spreading itself over the young plants and choking them.

All the motile stages may pass into resting stages, the small forms only surrounding themselves with a wall, but the large ones at the same time divide in addition into polyhedral cells. When favourable conditions arise, the walls dissolve and the whole appears again as a naked (free-moving) mass of protoplasm.

To the genuine Slime-Fungi belong: Arcyria, Trichia, Didymium, Physarum, Stemonitis, Lycogala, Fuligo, Spumaria, Reticularia.

Some genera wanting a sporangium-wall belong to the Slime-Fungi: Ceratiomyxa, whose fruit-body consists of polygonal plates, each bearing stalked spores; Dictyostelium, in which the swarm-stage is wanting and which has stalked spores. Plasmodiophora brassicæ preys upon the roots of cabbages and other cruciferous plants, causing large swellings. Pl. alni causes coral-shaped outgrowths on the roots of the Alder (Alnus). Phytomyxa leguminosarum may be found in small knobs (tubercles) on the roots of leguminous plants. It is still uncertain whether it is this Fungus or Bacteria which is the cause of the formation of these tubercles.

Sub-Division II.—ALGÆ.

Mode of Life. The Algæ (except most of the Bacteria) are themselves able to form their organic material by the splitting up of the carbonic acid contained in the water, or air in some cases, and for this purpose need light. The majority live in water, fresh or salt, but many are present on damp soil, stones, bark of trees, etc.

With the exception of the Bacteria, no saprophytes have actually been determined to belong to this group, and only very few true parasites (for instance, Phyllosiphon arisari, Mycoidea, etc.), but a good many are found epiphytic or endophytic on other Algæ, or water plants, and on animals (for instance, certain Schizophyceæ and Protococcoideæ; Trichophilus welckeri in the hairs of Bradypus, the Sloth), and several species in symbiotic relation to various Fungi (species of Lichen), to Sponges (e.g. Trentepohlia spongiophila, Struvea delicatula), and to sundry Infusoria and other lower animals as Radiolarias, Hydra, etc. (the so-called Zoochlorella and Zooxantella, which are perhaps partly stages in development of various Green and Brown Algæ).

Vegetative Organs. The cells in all the Algæ (excepting certain reproductive cells) are surrounded by a membrane which (with the exception of the Bacteria) consists of pure or altered cellulose, sometimes forming a gelatinous covering, at other times a harder one, with deposits of chalk or silica formed in it. The cell-nucleus, which in the Schizophyta is less differentiated, may be one or more (e.g. Hydrodictyon, Siphoneæ) in each cell. Excepting in the majority of the Bacteria, colour materials (of which chlorophyll, or modifications of it, always seems to be found) occur, which either permeate the whole cytoplasm surrounding the cell-nucleus, as in most of the coloured Schizophyta, or are contained in certain specially formed small portions of protoplasm (chromatophores).

The individual at a certain stage of development consists nearly always of only one cell; by its division multicellular individuals may arise, or, if the daughter-cells separate immediately after the division, as in many of the simplest forms, the individual will, during the whole course of its existence, consist of only a single cell (unicellular Algæ). In multicellular individuals the cells may be more or less firmly connected, and all the cells of the individual may be exactly alike, or a division of labour may take place, so that certain cells undertake certain functions, and are constructed accordingly; this may also occur in parts of the cell in the large unicellular and multinuclear Algæ (Siphoneæ, p. [62]).

The cells in most of the Algæ belong to the parenchymatous form; these, however, in the course of their growth, may very often become somewhat oblong; in many Algæ (particularly Fucoideæ and Florideæ) occur, moreover, hyphæ-like threads, which are very long, often branched, and are either formed of a single cell, or, more frequently, of a row of cells, having a well-pronounced apical growth. The parenchymatous as well as the hyphæ-like cells may, in the higher Algæ (especially in certain Fucoideæ and Florideæ), be further differentiated, so that they form well-defined anatomico-physiological systems of tissue, i.e. assimilating, conducting, storing, and mechanical.

With regard to the external form, the thallus may present no differentiation, as in many unicellular Algæ, or in multicellular Algæ of the lower order, which are then either equally developed in all directions (e.g. Pleurococcus, Fig. [47]), or form flat cell-plates (Merismopedium) or threads (Oscillaria, Fig. [21]). The first step in the way of differentiation appears as a difference between apex and base (Rivularia, Porphyra); but the division of labour may proceed so that differences may arise between vegetative and reproductive cells (Œdogonium, Fig. [54]); hairs and organs of attachment (rhizoids and haptera), which biologically serve as roots, are developed, and even leaves in certain forms of high order, belonging to different classes (e.g. Caulerpa, Fig. [59]; Characeæ, Fig. [61]; Sargassum, Fig. [72]; and many Florideæ).

The non-sexual reproduction takes place vegetatively, in many instances, simply by division into two, and more or less complete separation of the divisional products (Diatomaceæ, Desmidiaceæ (Fig. [36]), many Fission-plants, etc.), or by detached portions of the thallus (e.g. Caulerpa, Ulva lactuca, etc.; among many Schizophyceæ, small filaments known as hormogonia are set free), or asexually by special reproductive cells (spores) set free from the thallus; these may be either stationary or motile. The stationary reproductive cells (spores) may either be devoid of cell-wall (tetraspores of the Florideæ), or may possess a cell-wall; in the latter case they may be formed directly from the vegetative cells, generally by the thickening of the walls (akinetes), or only after a process of re-juvenescence (aplanospores). Aplanospores, as well as akinetes, may either germinate immediately or may become resting-cells, which germinate only after a period of rest.

The motile asexual reproductive cells are spherical, egg- or pear-shaped, naked, swarmspores (zoospores), which have arisen in other cells (zoosporangia), and propel themselves through the water by means of cilia; or they are Phyto-Amœbæ, which have no cilia and creep on a substratum by means of pseudopodia. The cilia, which are formed from the protoplasm (in the Bacteria, however, from the membrane), are mostly situated at the pointed and colourless end, which is directed forwards when in motion, and are 1, 2 (Fig. [5] B), 4 or more. Both the cilia in the Brown Algæ are attached to one side (Fig. [65]); they are occasionally situated in a circle round the front end (Œdogonium, Fig. [6] a, and Derbesia), or are very numerous and situated in pairs distributed over a large part or nearly the whole of the zoospore (Vaucheria). Besides being provided with one or more nuclei (Vaucheria), they may also have a red “eye spot” and vacuoles, which are sometimes pulsating, i.e. they appear and reappear at certain intervals. The swarmspores move about in the water in irregular paths, and apparently quite voluntarily, revolving round their longer axes; but they come to the surface of the water in great numbers either because of their dependence on light, or driven by warm currents in the water, or attracted by some passing mass of food material. The swarmspores germinate, each forming a new plant, as their movement ceases they surround themselves with a cell-wall, grow, and then divide; in Fig. [6] b, two may be seen in the condition of germination, and about to attach themselves by means of the front end, which has been developed into haptera (see also Fig. [5] B, lowest figure).

The sexual reproduction here, probably in all cases, consists in the coalescence of two masses of protoplasm, that is, in the fusion of their nuclei.

Fig. 5.—Cladophora glomerata. A The lower cells are full of swarmspores, whilst from the upper one the greater part have escaped through the aperture m. B Free and germinating swarmspores.

Fig. 6.—Œdogonium: a (free), b germinating swarmspores.

Fig. 7.—Zanardinia collaris. A Male gametangia (the small-celled) and female gametangia (large-celled). C Female gamete. D Male gamete. B E Fertilisation. F Zygote. G Germinating zygote.

The simplest and lowest form is termed conjugation, or isogamous fertilisation, and is characterized by the fact that the two coalescing cells (termed gametes) are equal, or almost equal, in shape and size (the female gamete in the Cutleriaceæ, e.g. Zanardinia collaris, Fig. [7], is considerably larger than the male gamete). The cell in which the gametes are developed is called a gametaugium, and the reproductive cell formed by their union—which generally has a thick wall and only germinates after a short period of rest—is termed a zygote or zygospore. The conjugation takes place in two ways:—

(a) In the one way the gametes are motile cells (planogametes, zoogametes, Fig. [8]), which unite in pairs during their swarming hither and thither in the water; during this process they lie side by side (Fig. [8] d), generally at first touching at the clear anterior end, and after a time they coalesce and become a motionless zygote, which surrounds itself with a cell-wall (Fig. [8] e). This form of conjugation is found in Ulothrix (Fig. [8] d), Acetabularia, and other Algæ (Figs. [45], [56], [66]).

Fig. 8.—Ulothrix zonata: a portion of a thread with zoospores, of which two are formed in each cell (zoosporangium), the dark spots upon them are the “red eye-spots”; 1, 2, 3, 4 depict successive stages in the development of the zoospores; b a single zoospore, at v the pulsating vacuole; c portion of a thread with gametes, of which sixteen are formed in each gametangium; d gametes free and in conjugation; e conjugation has been effected, and the formed zygotes are in the resting condition.

(b) Among other Algæ (e.g. Diatomaceæ and Conjugatæ), the conjugating cells continue to be surrounded by the cell-wall of the mother-cell (aplanogametes in an aplanogametangium); the aplanogametangia generally grow out into short branches, which lie close together and touch one another, the wall at the point of contact is then dissolved (Fig. [39]). Through the aperture thus formed, the aplanogametes unite, as in the first instance, and form a rounded zygote, which immediately surrounds itself with a cell-wall. Various modifications occur; compare Figs. [37], [39], [41], [43].

Fig. 9.—Fertilisation in the Bladder-wrack (Fucus vesiculosus).

Fig. 10.—Sphæroplea annulina.

The highest form of the sexual reproduction is the Egg- or Oogamous fertilisation. The two coalescing cells are in the main unlike each other in form as well as size. The one which is considered as the male, and is known as the spermatozoid (antherozoid), developes as a rule in large numbers in each mother-cell (antheridium); they are often self-motile (except in the Florideæ, where they are named spermatia), and are many times smaller than the other kind, the female, which is known as the egg-cell, (oosphere). The egg-cell is always a motionless, spherical, primordial cell which can either float about freely in the water, as in the Fucaceæ (Fig. [9]), or is surrounded by a cell-wall (oogonium); generally only one oosphere is to be found in each oogonium, but several occur in Sphæroplea (Fig. [10]). The result of the spermatozoid coalescing with the egg-cell is, as in this case, the formation of a oospore, which generally undergoes a period of rest before germination (the Florideæ are an exception, a fruit-body, cystocarp, being produced as the result of coalescence).

An example of fertilisation is afforded by the Alga, Sphæroplea annulina (Fig. [10]). The filamentous thallus is formed of cylindrical cells with many vacuoles (r in A); some cells develope egg-cells (B), others spermatozoids (C), the latter in a particularly large number. The egg-cells are spherical, the spermatozoids of a club- or elongated pear-shape with two cilia at the front end (G; E is however a swarmspore). The spermatozoids escape from their cells through apertures in the wall (o in C) and enter through similar apertures (o in B) to the egg-cells. The colourless front end of the spermatozoid is united at first with the “receptive spot” of the egg-cell (see F), and afterwards completely coalesces with it. The result is the formation of a oospore with wart-like excrescences (D).

The female (parthenogenesis) or male (androgenesis) sexual cell may, sometimes without any preceding fertilisation, form a new individual (e.g. Ulothrix zonata, Cylindrocapsa, etc.).

Systematic division of the Algæ. The Algæ are divided into the following ten classes:

1. Syngeneticæ; 2. Dinoflagellata, or Peridinea; 3. Diatomaceæ; 4. Schizophyta, Fission-algæ; 5. Conjugatæ; 6. Chlorophyceæ, Green-algæ; 7. Characeæ, Stone-worts; 8. Phæophyceæ; 9. Dictyotales; 10. Rhodophyceæ.

Among the lowest forms of the Algæ, the Syngeneticæ, the Dinoflagellata, and the unicellular Volvocaceæ (Chlamydomoneæ), distinct transitional forms are found approaching the animal kingdom, which can be grouped as animals or plants according to their method of taking food or other characteristics. Only an artificial boundary can therefore be drawn between the animal and vegetable kingdoms. In the following pages only those forms which possess chromatophores, and have no mouth, will be considered as Algæ.

Class 1. Syngeneticæ.

The individuals are uni- or multicellular, free-swimming or motionless. The cells (which in the multicellular forms are loosely connected together, often only by mucilaginous envelopes) are naked or surrounded by a mucilaginous cell-wall, in which silica is never embedded. They contain one cell-nucleus, one or more pulsating vacuoles, and one to two band- or plate-like chromatophores with a brown or yellow colour, and sometimes a pyrenoid.

Reproduction takes place by vegetative division, or asexually by zoospores, akinetes (or aplanospores?). Sexual reproduction is unknown. They are all fresh water forms.

To this class may perhaps be assigned the recently arranged and very little known orders of Calcocytaceæ, Murracytaceæ, Xanthellaceæ, and Dictyochaceæ, which partly occur in the free condition in the sea, in the so-called “Plankton,” and partly symbiotic in various lower marine animals.

The Syngeneticæ are closely related to certain forms in the animal kingdom, as the Flagellatæ.

Order 1. Chrysomonadinaceæ. Individuals, uni- or multicellular, swimming in free condition, naked or surrounded by a mucilaginous covering. The cells are generally oval or elongated, with 2 (rarely only 1) cilia, almost of the same length, and generally with a red “eye-spot” at their base, and with 2 (rarely 1 only) band-shaped chromatophores. Reproduction by the longitudinal division of the individual cells either during the swarming, or during a resting stage; in the multicellular forms also by the liberation of one or more cells, which in the latter case are connected together.

A. Unicellular: Chromulina, Cryptoglena, Microglena, Nephroselmis.

B. Multicellular: Uroglena, Syncrypta (Fig. [11]), Synura.

Fig. 11.—Syncrypta volvox: the multicellular individual is surrounded by a mucilaginous granular envelope.

Among the unicellular Chrysomonadinaceæ are probably classed some forms which are only stages in the development of the multicellular, or of other Syngeneticæ.

Order 2. Chrysopyxaceæ are unicellular, and differ mainly from the preceding in being attached either on a slime-thread (Stylochrysalis), or enclosed in an envelope (Chrysopyxis, Fig. [12]). They have two cilia, and multiply by longitudinal (Chrysopyxis) or transverse division, and the swarming of one of the daughter-individuals (zoospore). Division may also take place in a motionless stage (palmella-stage).

Fig. 12.—Chrsopyxis bipes: m envelope, Ec chromatophore, cv contractile vacuole.

Order 3. Dinobryinaceæ. The individuals are originally attached, uni- or multicellular; each individual cell is distinctly contractile, and fixed at the bottom of a cup-shaped, open envelope. Cilia 2, but of unequal length. Asexual reproduction by zoospores, which are formed by straight or oblique longitudinal division of the mother-cell, during a palmella-stage which is produced in the winter aplanospores. Epipyxis, Dinobryon.

Order 4. Hydruraceæ. The individuals are attached, without cilia, multicellular, branched, and with apical growth. The cells are spherical, but in the final stage almost spindle-shaped, and embedded in large masses of mucilage. Asexual reproduction by zoospores which are tetrahedric, with 1 cilia, and by resting akinetes. Hydrurus is most common in mountain brooks.

Class 2. Dinoflagellata.

The individuals are of a very variable form, but always unicellular, and floating about in free condition. The cell is dorsiventral, bilateral, asymmetric and generally surrounded by a colourless membrane, which has no silica embedded in it, but is formed of a substance allied to cellulose. The membrane, which externally is provided with pores and raised borders, easily breaks up into irregularly-shaped pieces. In the forms which have longitudinal and cross furrows, two cilia are fixed where these cross each other, and project through a cleft in the membrane; one of these cilia projects freely and is directed longitudinally to the front or to the rear, the other one stretches crosswise and lies close to the cell, often in a furrow (cross furrow). The chromatophores are coloured brown or green and may either be two parallel (Exuviella), or several radially placed, discs, which sometimes may coalesce and become a star-shaped chromatophore. The coloring material (pyrrophyl) consists, in addition to a modification of chlorophyl, also of phycopyrrin and peridinin; this colour is sometimes more or less masked by the products of assimilation which consist of yellow, red or colourless oil (?) and starch. Cell-nucleus one: in Polydinida several nuclei are found; contractile vacuoles many, which partly open in the cilia-cleft (Fig. [13] gs). In some an eye-spot, coloured red by hæmatochrome, is found. Pyrenoids occur perhaps in Exuviella and Amphidinium.

The reproduction takes place as far as is known at present, only by division. This, in many salt water forms, may take place in the swarming condition, and, in that case, is always parallel to the longitudinal axis. The daughter-individuals, each of which retains half of the original shell, sometimes do not separate at once from each other, and thus chains (e.g. in Ceratium) of several connected individuals may be formed. In others, the division occurs after the cilia have been thrown off and the cell-contents rounded. The daughter-cells then adopt entirely new cell-walls. A palmella-stage (motionless division-stage) sometimes appears to take place, and also aplanospores (?) with one or two horn-like elongations (e.g. in Peridinium cinctum and P. tabulatum); at germination one, or after division, two or more, new individuals may be formed.

Sexual reproduction has not been observed with certainty.

The Dinoflagellata move forward or backward, turning round their longitudinal axes; in their motion they are influenced by the action of light. The motion possibly may be produced only by the transverse cilium, which vibrates rapidly; whilst the longitudinal cilium moves slowly, and is supposed to serve mainly as a steering apparatus. They live principally in salt water, but also in fresh.

Besides the coloured forms, which are able to make their own organic compounds by the splitting up of the carbonic acid contained in the water, there are a few colourless forms (e.g. Gymnodinium spirale), or such as do not possess chromatophores (Polykrikos); these appear to live saprophytically, and may be able to absorb solid bodies with which they come in contact.

Dinoflagellata occur in the “Plankton” of the open sea, where they form together with Diatomaceæ the basis for the animal life. It is known with certainty that some salt water forms (like the Noctiluca, which belongs to the animal kingdom and to which they are perhaps related) produce light, known as phosphorescence.

Fig. 13.—A and B Glenodinium cinctum. A seen from the ventral side, B from behind; fg transverse cilium; g longitudinal cilium; ch chromatophores; a starch; n cell-nucleus; v vacuole; oc eye-spot; C Ceratium tetraceros from the ventral side; r the right, b the posterior horn; lf longitudinal furrow; gs cilium-cleft; v vacuole; g longitudinal cilium. (A and B mag. 450 times, C 337 times.)

Dinoflagellata (Peridinea, Cilioflagellata) are allied through their lowest form (Exuviella) to the Syngeneticæ and especially to the order Chrysomonadinaceæ. They may be divided into three orders.

Order 1. Adinida. Without transverse or longitudinal furrows, but enclosed in two shells, and with two parallel chromatophores in each cell. Exuviella, Prorocentrum.

Order 2. Dinifera. With tranverse and generally longitudinal furrow. Many radially-placed, disc-formed chromatophores. The most common genera are—Ceratium (Fig. [13]), Peridinium, Glenodinium (Fig. [13]), Gymnodinium, Dinophysis.

Order 3. Polydinida. With several transverse furrows, no chromatophores, and several cell-nuclei. Only one genus—Polykrikos.

The order Polydinida deviates in a high degree from the other Dinoflagellata, not only by its many tranverse furrows, each with its own transverse cilium, and by the absence of chromatophores, but also in having several cell-nuclei and a kind of stinging capsule, which otherwise does not occur within the whole class. It may therefore be questionable whether this order should really be placed in the vegetable kingdom.

Class 3. Diatomeæ.

The individuals—each known as a frustule—assume very various forms and may be unicellular or multicellular, but present no differentiation; many similar cells may be connected in chains, embedded in mucilaginous masses, or attached to mucilaginous stalks. The cells are bilateral or centric, often asymmetrical, slightly dorsiventral and have no cilia; those living in the free condition have the power of sliding upon a firm substratum. The cell contains 1 cell-nucleus and 1–2 plate-shaped or several disc-shaped chromatophores. The colouring material “Melinophyl” contains, in addition to a modification of chlorophyl, a brown colouring matter, diatomin. 1 or 2 pyrenoids sometimes occur. Starch is wanting and the first product of assimilation appears to be a kind of oil (?).

Fig. 14.—Pinnularia: B, from the edge, shows the valves fitting together; A, a valve.

Fig. 15.—Various Diatomaceæ. A Diatoma vulgare. B Tabellaria flocculosa. C Navicula tumida (lateral views). D Gomphonema constrictum (lateral views). E Navicula west[=i][=i] (lateral views).

The cell-walls are impregnated with silica to such a degree that they are imperishable and are therefore able to contribute in a great measure to the formation of the earth’s crust. The structure of their cell-wall is most peculiar and differs from all other plants (except certain Desmidiaceæ); it does not consist of a single piece but is made up of two—the “shells”—(compare Exuviella and Prorocentrum among the Dinoflagellata) which are fitted into each other, one being a little larger than the other and embracing its edge, like a box with its lid (Fig. [14] B). The two parts which correspond to the bottom and lid of the box are known as valves. Along the central line of the valves a longitudinal rib may often be found, interrupted at its centre by a small cleft (perhaps homologous with the cilia-cleft of the Dinoflagellata), through which the protoplasm is enabled to communicate with the exterior (Fig. [14] A). It is principally by reason of the valves, which bear numerous fine, transverse ribs, striæ or warts, etc. (Figs. [14], [15], [17]), that the Diatomeæ have become so well known and employed as test objects in microscopical science. When the division takes place, the two shells are separated a little from each other, and after the cell-contents have divided into two masses, two new shells are formed, one fitting into the larger valve, the other one into the smaller valve of the original frustule. The latter cell (frustule) is thus, upon the whole, smaller than the mother-cell, and as the cells do not increase in size, some frustules are smaller than the ones from which they are derived, and thus, by repeated divisions, it follows that smaller and smaller frustules are produced. This continued diminution in size is, however, compensated for by the formation, when the cells have been reduced to a certain minimum, of auxospores, 2–3 times larger. These may either be formed asexually by the protoplasm of a cell increasing, rounding off and surrounding itself with a new wall (e.g. Melosira) or after conjugation, which may take place with various modifications: 1. Two individuals unite after the secretion of a quantity of mucilage, and the valves then commence to separate from each other, on the side which the two individuals turn towards each other. The protoplasmic bodies now release themselves from their cell-wall, and each rounds off to form an ellipsoidal mass; these two protoplasmic masses (gametes) coalesce to form a zygote, the cell-nuclei and chromatophores also fusing together. The zygote increases in size, and surrounds itself with a firm, smooth, siliceous wall—the perizonium. The auxospores, whichever way they arise, are not resting stages. The germination of the zygote commences by the protoplasm withdrawing itself slightly from the cell-wall and constructing first the larger valve, and later on the smaller one; finally the membrane of the zygote bursts (e.g. Himantidium). 2. The conjugation occurs in a similar manner, but the protoplasm of the cells divides transversely before conjugation into two daughter-cells. Those lying opposite one another conjugate (Fig. [16]) and form two zygotes. The formation of the perizonium, and germination take place as in the preceding instance (e.g. Epithemia). 3. Two cells place themselves parallel to each other, and each of the two cell-contents, without coalescing, becomes an auxospore. The formation of the wall takes place as in the preceding case. This is found in the Naviculeæ, Cymbelleæ, the Gomphonemeæ (e.g. Frustulia, Cocconema).

Fig. 16.—Conjugation of Cymbella variabilis. A, The protoplasm in the two cells has divided into two masses; B these masses coalesce in pairs; the cells (B C) enclosed in a mucilaginous matrix. C D Auxospores and their formation.

The Diatomaceæ may be found in salt as well as in fresh water (often in such masses that the colour of the water or mud becomes yellow or brown; in the same manner the genera Chætoceros, Rhizosolenia, Coscinodiscus, and several others, form large slime-masses, “Plankton” on the surface of the sea), on damp soil and in dust blown by the wind. They occur as fossils in the recent formations, often in large deposits (siliceous earth, mountain meal), as in the cement lime in Jutland, the alluvial deposits beneath Berlin, in clay strata beneath peat bogs, in guano, etc. These accumulations of fossilized diatoms are used in the manufacture of dynamite and in various manufactures.

The Diatomaceæ appear nearest to, and must be placed as a group co-ordinate with the Dinoflagellata, as they doubtless may be supposed to derive their origin from forms resembling Exuviella, and to have lost the cilia. The resemblances to the Desmidiaceæ which are striking in many respects, can only be conceived as analogies, and cannot be founded upon homologies, and it is therefore impossible to regard them as proof of genetic relationship. The family contains only one order.

Fig. 17.—Various Diatomeæ. A Synedra radians. B Epithemia turgida (from the two different sides). C Cymbella cuspidata. D Cocconeis pediculus (on the right several situated on a portion of a plant, on the left a single one more highly magnified).

Order 1. Diatomaceæ. This order may be divided into two sub-orders, viz.—

Sub-Order 1. Placochromaticæ. The chromatophores are discoid, large, 1 or 2 in each cell; the structure of the valves is bilateral and always without reticulate markings. The following groups belong to this sub-order: Gomphonemeæ, Cymbelleæ, Amphoreæ, Achnantheæ, Cocconeideæ, Naviculeæ, Amphipleureæ, Plagiotropideæ, Amphitropideæ, Nitzchieæ, Surirayeæ, and Eunotieæ.

Sub-Order 2. Coccochromaticæ. The chromatophores are granular, small and many in each cell. The structure of the cells is zygomorphic or centric, often with reticulate markings. The following groups belong to this sub-order: Fragilarieæ, Meridieæ, Tabellarieæ, Licmophoreæ, Biddulphieæ, Anguliferæ, Eupodisceæ, Coscinodisceæ, and Melosireæ.

Class 4. Schizophyta, Fission-Algæ.

The individuals are 1—many celled; the thallus consists in many of a single cell, in others of chains of cells, the cells dividing in only one definite direction (Figs. [18], [21]). In certain Fission-Algæ the cell-chain branches (Fig. [30]) and a difference between the anterior and the posterior ends of the chain is marked; in some, the cells may be united into the form of flat plates by the cell-division taking place in two directions; and in others into somewhat cubical masses, or rounded lumps of a less decided form, by the divisions taking place in three directions; or less defined masses may be formed by the divisions taking place in all possible directions.

The cell-walls rarely contain cellulose, they often swell considerably (Figs. [20], [22]), and show distinct stratifications, or they are almost completely changed into a mucilaginous mass in which the protoplasts are embedded, e.g. in Nostoc (Fig. [22]), and in the “Zooglœa” stage of the Bacteria (Fig. [27]). Sexual reproduction is wanting. Vegetative reproduction by division and the separation of the divisional products by the splitting of the cell-wall or its becoming mucilaginous; among the Nostocaceæ, Lyngbyaceæ, Scytonemaceæ, etc., “Hormogonia” are found; in Chamæsiphon and others single reproductive akinetes are formed. Many Fission-Algæ conclude the growing period by the formation of resting akinetes or aplanospores.

The Schizophyta may be divided into 2 families:

1. Schizophyceæ.

2. Bacteria.

Family 1. Schizophyceæ,[5] Blue-Green Algæ.

All the Blue-green Algæ are able to assimilate carbon by means of a colouring material containing chlorophyll (cyanophyll); but the chlorophyll in this substance is masked by a blue (phycocyan), or red (phycoerythrin, e.g. in Trichodesmium erythræum in the Red Sea) colouring matter which may be extracted from them in cold water after death. The colouring matter, in most of them, permeates the whole of the protoplasm (excepting the cell-nucleus), but in a few (e.g. Glaucocystis, Phragmonema), slightly developed chromatophores are to be found. Where the cells are united into filaments (cell-chains) a differentiation into apex and base (Rivulariaceæ) may take place, and also between ordinary vegetative cells and heterocysts; these latter cannot divide, and are distinguished from the ordinary vegetative cells (Fig. [22] h) by their larger size, yellow colour, and poverty of contents. Branching sometimes occurs and is either true or spurious.

Fig. 18.—Microcoleus lyngbyanus: a portion of a filament, the thick sheath encloses only one cell-chain; in one place a cell is drawn out by the movement of the cell-chain; b the cell-chain has divided into two parts (“hormongonia”) which commence to separate from each other.

The cell-chain in the spurious branching divides into two parts, of which either one or both grow beyond the place of division (Fig. [18]) and often out to both sides (e.g. Scytonema), the divisions however, always take place transversely to the longitudinal direction of the cell-chain. In the true branching a cell elongates in the direction transverse to the cell-chain, and the division then takes place nearly at right angles to the former direction (Sirosiphoniaceæ).

Fig. 19.—Cylindrospermum majus: a resting akinete with heterocyst; b-d germinating stages of a resting akinete; e filament with two heterocysts and the formation of new akinetes; f part of a filament with a heterocyst, and mature resting akinete.

Cilia are wanting, but the filaments are sometimes self-motile (e.g. hormogonia in Nostoc) and many partly turn round their axes, partly slide forward or backward (Oscillaria).

Reproduction takes place by spores and hormogonia in addition to simple cell-division. Hormogonia are peculiar fragments of a cell-chain capable of motion, and often exhibit a vigorous motion in the sheath, until at last they escape and grow into a new individual (Fig. [18]). The spores are reproductive akinetes (Chamæsiphon, etc.) or resting akinetes; these latter arise by the vegetative cells enlarging and constructing a thick cell-wall (Fig. [19] e f). On germination, this cell-wall bursts and the new cell-chain elongates in the same longitudinal direction as before (Fig. [19] b c). Many (e.g. Oscillaria) may however winter in their ordinary vegetative stage. Aplanospores are wanting.

The Fission-Algæ are very prevalent in fresh water and on damp soil, less so in salt water; they also often occur in water which abounds in decaying matter. Some are found in warm springs with a temperature as high as 50° C.

The Family may be divided into 2 sub-families:

1. Homocysteæ (heterocysts are wanting): Chroococcaceæ, Lyngbyaceæ and Chamœsiphonaceæ.

2. Heterocysteæ (heterocysts present): Nostocaceæ, Rivulariaceæ, Scytonemaceæ and Sirosiphoniaceæ.

Order 1. Chroococcaceæ. The individuals are 1—many-celled, but all the cells are uniform, united to form plates or irregular masses, often surrounded by a mucilaginous cell-wall, but never forming cell-chains. Multiplication by division and sometimes by resting akinetes, but reproductive akinetes are wanting. Chroococcus, Aphanocapsa, Glœocapsa (Fig. [20]), Cœlosphærium, Merismopedium, Glaucocystis, Oncobyrsa, Polycystis, Gomphosphæria.

Fig. 20.—Glœocapsa atrata: A, B, C, D, E various stages of development.

Fig. 21.—Oscillaria; a terminal, b central portion of a filament.

Order 2. Lyngbyaceæ (Oscillariaceæ). The cells are discoid (Fig. [21]), united to straight or spirally twisted, free filaments, which are unbranched, or with spurious branching. The ends of the cell-chains are similar. Heterocysts absent. Reproduction by synakinetes, resting akinetes are wanting. Oscillaria (Fig. [21]), Spirulina, Lyngbya, Microcoleus, Symploca, Plectonema.

Order 3. Chamæsiphonaceæ. The individuals are 1—many-celled, attached, unbranched filaments with differentiation into apex and base, without heterocysts. Multiplication by reproductive akinetes; resting akinetes are wanting. Dermocarpa, Clastidium, Chamæsiphon, Godlewskia, Phragmonema.

Order 4. Nostocaceæ. The individuals are formed of multicellular, unbranched filaments, without differentiation into apex and base; heterocysts present. Reproduction by synakinetes and resting akinetes.

Fig. 22.—Nostoc verrucosum. A The plant in its natural size; an irregularly folded jelly-like mass. B One of the cell-chains enlarged, with its heterocysts (h), embedded in its mucilaginous sheath.

Some genera are not mucilaginous, e.g. Cylindrospermum (Fig. [19]). The cell-chains in others, e.g. Nostoc, wind in between one another and are embedded in large structureless jelly-like masses, which may attain the size of a plum or even larger (Fig. [22]); sometimes they are found floating in the water, sometimes attached to other bodies. Other genera as follows: Aphanizomenon and Anabæna (in lakes and smaller pieces of water); Nodularia is partly pelagic. Some occur in the intercellular spaces of higher plants, thus Nostoc-forms are found in Anthoceros, Blasia, Sphagnum, Lemna, and in the roots of Cycas and Gunnera; Anabæna in Azolla.

Order 5. Rivulariaceæ. The individuals are multicellular filaments, with differentiation into apex and base; spurious branching, and a heterocyst at the base of each filament, reproduction by synakinetes and resting akinetes, rarely by simple reproductive akinetes. Rivularia, Glœotrichia, Isactis, Calothrix.

Order 6. Scytonemaceæ. The individuals are formed of multicellular filaments with no longitudinal division; differentiation into apex and base very slight or altogether absent; branching spurious; heterocysts present. Reproduction by synakinetes, rarely by resting akinetes and ordinary reproductive akinetes. Tolypothrix, Scytonema, Hassalia, Microchæte.

Order 7. Sirosiphoniaceæ. The individuals are formed of multicellular threads with longitudinal divisions; true branching and heterocysts, and often distinct differentiation into apex and base. Reproduction by synakinetes, rarely by resting akinetes and ordinary reproductive akinetes. Hapalosiphon, Stigonema, Capsosira, Nostocopsis, Mastigocoleus.

Family 2. Bacteria.[6]

The Bacteria (also known as Schizomycetes, and Fission-Fungi) are the smallest known organisms, and form a parallel group to the Blue-green Algæ, but separated from these Algæ by the absence of their colouring material; chlorophyll is only found in a few Bacteria.

The various forms under which the vegetative condition of the Bacteria appear, are termed as follows:

1. Globular forms, cocci (Figs. [27], [30] c): spherical or ellipsoidal, single cells, which, however, are usually loosely massed together and generally termed “Micrococci.”

2. Rod-like forms: more or less elongated bodies; the shorter forms have been styled “Bacterium” (in the narrower sense of the word), and the term “Bacillus” has been applied to longer forms which are straight and cylindrical (Figs. [28], [29], [30] E).

Fig. 23.—Spirillum sanguineum. Four specimens. One has two cilia at the same end, the sulphur grains are seen internally.

3. Thread-like forms: unbranched, long, round filaments, resembling those of Oscillaria, are possessed by Leptothrix (very thin, non-granular filaments; Fig. [30] A, the small filaments) and Beggiatoa (thicker filaments, with strong, refractile grains or drops of sulphur (Fig. [31]); often self-motile). Branched filaments, with false branching like many Scytonemaceæ, are found in Cladothrix (Fig. [30] B, G).

4. Spiral forms: Rod-like or filamentous bodies, which more or less strongly resemble a corkscrew with a spiral rising to the left. In general these are termed Spirilla (Fig. [23]); very attenuated spirals, Vibriones (standing next to Fig. [30] M); if the filaments are slender and flexible with a closely wound spiral, Spirochætæ (Fig. [24]).

5. The Merismopedium-form, consisting of rounded cells arranged in one plane, generally in groups of four, and produced by divisions perpendicular to each other.

6. The Sarcina-form, consisting of roundish cells which are produced by cellular division in all the three directions of space, united into globular or ovoid masses (“parcels”) e.g. Sarcina ventriculi (Figs. [25], [26]).

Fig. 24.—Spirochæte obermeieri, in active motion (b) and shortly before the termination of the fever (c); a blood corpuscles.

All Bacteria are unicellular. In the case of the micrococci this is self-evident, but in the “rod,” “thread,” and “spiral” Bacteria, very often numerous cells remain united together and their individual elements can only be recognised by the use of special reagents.

Fig. 25.—Sarcina ventriculi. One surface only is generally seen. Those cells which are drawn with double contour are seen with the correct focus, and more distinctly than those cells lying deeper drawn with single contour.

Fig. 26.—Sarcina minuta: a-d successive stages of one individual (from 4–10 p.m.); f an individual of 32 cells.

The condition termed “Zooglœa,” which reminds us of Nostoc, is produced by the cells becoming strongly mucilaginous. A number of individuals in active division are found embedded in a mass of mucilage, which either contains only one, or sometimes more, of the above-named forms. The individuals may eventually swarm out and continue their development in an isolated condition. Such mucilaginous masses occur especially upon moist vegetables (potatoes, etc.), on the surface of fluids with decaying raw or cooked materials, etc. The mucilaginous envelope is thrown into folds when the Bacteria, with their mucilaginous cell-walls, multiply so rapidly that there is no more room on the surface of the fluid.

The cells of the Bacteria are constructed like other plant-cells in so far as their diminutive size has allowed us to observe them. The cell-wall only exceptionally shows the reactions of cellulose (in Sarcina, Leuconostoc; also in a Vinegar-bacterium, Bacterium xylinum); a mucilaginous external layer is always present. The body of the cell mostly appears to be an uniform or finely granulated protoplasm. Very few species (e.g. Bacillus virens) contain chlorophyll; others are coloured red (purple sulphur Bacteria); the majority are colourless. Bacillus amylobacter shows a reaction of a starch-like material when treated with iodine before the spore-formation. Some Bacteria contain sulphur (see p. [37]). The body, which has been described as a cell-nucleus, is still of a doubtful nature.

Artificial colourings with aniline dyes (especially methyl-violet, gentian-violet, methylene-blue, fuchsin, Bismarck-brown and Vesuvin) play an important part in the investigations of Bacteria.

Movement. Many Bacteria are self-motile; the long filaments of Beggiatoa exhibit movements resembling those of Oscillaria. In many motile forms the presence of cilia or flagella has been proved by the use of stains; many forms have one, others several cilia attached at one or both ends (Fig. [23]) or distributed irregularly over the whole body; the cilia are apparently elongations of the mucilaginous covering and not, as in the other Algæ of the protoplasm. In Spirochæte the movement is produced by the flexibility of the cell itself. Generally speaking, the motion resembles that of swarm-cells (i.e. rotation round the long axis and movement in irregular paths); but either end has an equal power of proceeding forwards.

The swarming motion must not be confounded with the hopping motion of the very minute particles under the microscope (Brownian movement).

Vegetative reproduction takes place by continued transverse division; hence the name “Fission-Fungi” or “Fission-Algæ,” has been applied to the Bacteria.

Spores. The spores are probably developed in two ways. In the ENDOSPOROUS species (Figs. [28], [29]), the spore arises as a new cell inside the mother-cell. The spores are strongly refractile, smaller than the mother-cell, and may be compared to the aplanospores of other Algæ. In addition to these there are the ARTHROSPOROUS species in which the cells, just as in Nostoc and other Blue-green Algæ, assume the properties of spores without previously undergoing an endogenous new construction, and are able to germinate and form new vegetative generations (Fig. [27]). The formation of spores very often commences when the vegetative development begins to be restricted.

Fig. 27.—Leuconostoc mesenterioides: a a zooglœa, natural size; b cross section of zooglœa; c filaments with spores; d mature spores; e-i successive stages of germination; in e portions of the ruptured spore-wall are seen on the external side of the mucilaginous covering. (b-i magnified 520.)

The spores germinate as in Nostoc by the bursting of the external layer of the cell-wall, either by a transverse or longitudinal cleft, but always in the same way, in the same species (Fig. [28], example of transverse cleft).

Distribution. Bacteria and their germs capable of development, are found everywhere, in the air (dust), in surface water, and in the superficial layers of the soil. The number varies very much in accordance with the nature of the place, season, etc. They enter, together with air and food, into healthy animals and occur always in their alimentary tract.

Growth and reproduction depend upon the conditions of temperature. There is a certain minimum, optimum and maximum for each species; for instance (in degrees Centigrade)—

Fig. 28.—Bacillus megaterium: a outline of a living, vegetative cell-rod; b a living, motile, pair of rods; p a similar 4-celled rod after the effects of iodine alcohol; c a 5-celled rod in the first stages of spore-formation; d-f successive stages of spore-formation in one and the same pair of rods (in the course of an afternoon); r a rod with mature spores; g¹–g³ three stages of a 5-celled rod, with spores sown in nutritive solution; h¹–h², i, k, l stages of germination; m a rod in the act of transverse division, grown out from a spore which had been sown eight hours previously. (After de Bary; a mag. 250, the other figures 600 times).

Fig. 29.—Bacillus amylobacter. Motile rods, partly cylindrical and without spores, partly swollen into various special shapes and with spore-formation in the swelling. s Mature spore, with thick mucilaginous envelope. (After de Bary; mag. 600 times, with the exception of s, which is more highly magnified.)

The functions of life cease on a slight excess of the maximum or minimum temperature, numbness setting in when either of these limits is passed. Crenothrix-threads provided with mucilaginous envelopes may, according to Zopf, sustain a temperature of-10°. Some Bacteria are said to be able to resist the exposure to as low a temperature as-110° for a short time. It is not known at what degree of cold the death of the Bacteria occurs: the greatest degree of heat which the vegetative cells can withstand is about the same as that for other vegetative plant-cells, namely, about 50–60° C. Certain Bacteria, e.g. B. thermophilus, grow and thrive vigorously at 70° C. Many spores, on the contrary, are able to bear far higher temperatures (in several species a temperature for some duration of above 100°, those of Bacillus subtilis, for instance, can withstand for hours a temperature of 100° in nutrient solutions; the spores remain capable of development after exposure to a dry heat of 123° C.).

The Desiccation of the air, if prolonged, kills many forms when in the vegetative condition. The spores however can bear a much longer period of dryness, some even several years.

Oxygen. Some species cannot live without a supply of free oxygen (Aerobic), e.g. the Vinegar-bacteria, the Hay-bacilli, the Anthrax-bacilli, the Cholera-Microspira. Other species again thrive vigorously without supply of free oxygen, and are even checked in their development by the admission of air (Anaerobic), e.g. the butyric acid Bacterium (Clostridium butyricium = Bacillus amylobacter). A distinction may be drawn between obligate and facultative aerobics and obligate and facultative anaerobics. Several Bacteria, producing fermentation, may grow without the aid of oxygen when they are living in a solution in which they can produce fermentation; but, if this is not the case, they can only grow when a supply of oxygen is available. A great number of the pathogenic Bacteria belong to the facultative anaerobics.

A luminous Bacterium (Bacillus phosphorescens) which in the presence of a supply of oxygen gives a bluish-white light, has been found in sea-water. Phosphorescent Bacteria have frequently been observed upon decaying sea-fish, as well as on the flesh of other animals; by transferring the Bacteria from cod fish to beef, etc., the latter may be made luminous.

Organic carbon compounds are indispensable for all Bacteria, (except, as it appears, for the nitrifying organisms), as they can only obtain the necessary supplies of carbon from this source. The supplies of nitrogen, which also they cannot do without, can be obtained equally as well from organic compounds as from inorganic salts, such as saltpetre or ammonia-compounds. The various “ash-constituents” are also essential for their nourishment.

While Moulds and Yeast-Fungi grow best in an acid substratum, the Bacteria, on the other hand, generally thrive best in a neutral or slightly alkaline one.

In sterilization, disinfection, and antisepsis, means are employed by which the Bacteria are killed, or checked in their development, for instance, by heat (ignition, cooking, hot vapours, hot air, etc.), or poisons (acids, corrosive sublimate). The process of preserving articles of food, in which they are boiled and then hermetically sealed, aims at destroying the Bacteria, or the spores of those which already may be present in them, and excluding all others.

As the Bacteria are unable to assimilate carbon from the carbonic acid of the air, but must obtain it from the carbon-compounds already in existence in the organic world, they are either saprophytes or parasites. Some are exclusively either the one or the other, obligate saprophytes or parasites. But there are transitional forms among them, some of which are at ordinary times saprophytes, but may, when occasion offers, complete their development wholly or partly as parasites—facultative parasites; others are generally parasitic, but may also pass certain stages of development as saprophytes—facultative saprophytes.

All chlorophyll-free organisms act in a transforming and disturbing manner on the organic compounds from which they obtain their nourishment, and while they themselves grow and multiply, they produce, each after its kind, compounds of a less degree of complexity, i.e. they produce fermentation, putrefaction, sometimes the formation of poisons, and in living beings often disease.

Those organisms which produce fermentation are called ferments; this word, however, is also employed for similar transformations in purely chemical materials (inorganic ferments or enzymes). Many organic (“living”) ferments, among which are Yeast-cells and Bacteria, give off during their development certain inorganic and soluble ferments (enzymes) which may produce other transformations without themselves being changed. Different organisms may produce in the same substratum different kinds of transformation; alcoholic fermentation may for instance be produced by different species of Fungi, but in different proportions, and the same species produces in different substrata, different transformations (e.g. the Vinegar-bacteria oxydize diluted alcohol to vinegar, and eventually to carbonic acid and water).

In the study of Bacteria it is absolutely necessary to sterilize the vessels employed in cultivation, the apparatus, and nutrient solutions, i.e. to free them from Bacteria germs and also to preserve the cultures from the intrusion of any foreign germs (“pure-cultures”). A firm, transparent, nutritive medium is frequently employed. This may be prepared by adding to the nutrient solutions (broth) either gelatine, or—when the Bacteria are to be cultivated at blood-heat—serum of sheep’s or calf’s blood, agar-agar or carragen; serum alone may in itself serve as a nutrient medium. The so-called “plate-cultures” are frequently employed, i.e. the germs are isolated by shaking them with the melted liquid nutrient gelatine, which is then spread on a glass plate and allowed to coagulate; when later on the individual germs grow into colonies, these remain separate in the solid substratum and it is easy to pursue their further development. Similar plate-cultures may also be cultivated in test-tubes and on microscopic slides. The slides and glass plates must be placed in “moist chambers” free from Bacteria. By sowing a few cells (if possible one) using a fine platinum wire, pure cultures for further investigation may be obtained.

In order to prove the relationship between pathogenic Bacteria and certain diseases, the experimental production of pathogenic Bacteria by the inoculation of Bacteria from pure cultures into healthy animals, is very important.

It has not so far been possible to establish a classification of the Bacteria, as the life-history of many species, has not yet been sufficiently investigated.[7] The opinions of botanists are at variance, in many cases, about the forms of growth of a particular kind. Some species are pleomorphic (many-formed) while others possess only one form.

The following Bacteria are Saprophytes:—

Cladothrix dichotoma is common in stagnant and running water which is impregnated with organic matter; the cell-chains have false branching. According to Zopf, Leptothrix ochracea is one of the forms of this species which, in water containing ferrous iron (e.g. as FeCO₃), regularly embeds ferric-oxide in its sheath by means of the activity of the protoplasm. Leptothrix ochracea and other Iron-bacteria, according to Winogradsky (1888), do not continue their growth in water free from protoxide of iron; while they multiply enormously in water which contains this salt of iron. The large masses of ochre-coloured slime, found in meadows, bogs, and lakes, are probably due to the activity of the Iron-bacteria.

Fig. 30.—Cladothrix dichotoma.

Those forms which, according to Zopf’s views, represent the forms of development of Cladothrix dichotoma are placed together in Fig. [30]. A represents a group of plants, seventy times magnified, attached to a Vaucheria. The largest one is branched like a tree, with branches of ordinary form; a specimen with spirally twisted branches is seen to the right of the figure, at the lower part some small Leptothrix-like forms. B shows the manner of branching and an incipient Coccus-formation. C a Coccus-mass whose exit from the sheath has been observed. D the same mass as C after the course of a day, the Cocci having turned into rods. E a group of Cocci in which some have developed into shorter or longer rods. F one of these rods before and after treatment with picric acid, which causes the chain-like structure to become apparent. G a portion of a plant with conspicuous sheath, two lateral branches are being formed. H part of a plant, whose cells have divided and form Cocci. The original form of the cells in which the Cocci are embedded may still be recognised. I. Leptothrix-filaments with conspicuous mucilaginous sheath, from which a series of rods is about to emerge; the rod near the bottom is dead, and has remained lying in the sheath. K part of a plant which is forming Cocci, those at the top are in the zooglœa-stage, at the base they are elongating to form rods and Leptothrix-filaments. L a portion of a branched Cladothrix, which divides into motile Bacillus-forms; the rays at the free ends indicate the currents which the cilia produce in the water. M a spirally-twisted, swarming filament, before and after division into halves. N part of a tree-like zooglœa with Cocci and short rods.—All of these spirilla, zooglœa, etc., which Zopf has connected with Clad. dichotoma, are according to Winogradsky, independent organisms.

Micrococcus ureæ produces urinal fermentation (transformation of urinal matter into ammonium carbonate); aerobic; round cells generally united to form bent chains or a zooglœa.—Several other kinds of Bacteria have the same action as this one: in damp soil containing ammonia-compounds, saltpetre-formations are produced by M. nitrificans and several different kinds of Bacteria.

Micrococcus prodigiosus is found on articles of food containing starch; “bleeding bread” is caused by this Bacterium, which has the power of forming a red pigment; it also occurs in milk, and produces lactic acid.

Leuconostoc mesenterioides is the frog-spawn Bacterium (Fig. [27]) which is found in sugar manufactories, and has the power of producing a viscous fermentation in saccharine solutions which have been derived from plants, e.g. in beetroot-sugar manufactories, where large accumulations of mucilage are formed at the expense of the sugar, with an evolution of carbonic acid. The cell-rows, resembling somewhat a pearl necklace, have thick mucilaginous cell-walls, and form white “Nostoc”-lumps. The mucilage eventually deliquesces and the cells separate from each other; arthrospores?—Similar viscous deteriorations occur in beer and wine, which may then be drawn out into long, string like filaments—“ropiness.”

Bacterium aceti, the Vinegar-bacterium, oxidizes alcohol into acetic acid (acetous-fermentation) and forms a greyish covering of Bacteria (“Vinegar-mother”) on the surface of the liquid; the acetic acid formed, becomes by continued oxidization by B. aceti, again transformed into carbonic acid and water. Aerobic; short cylindrical cells, often united into chains, or to form a zooglœa; sometimes also rod-and spindle-shaped. The Vinegar-bacteria and other kinds with ball- or rod-forms sometimes become swollen, spindle-shaped, or oval links; they are supposed to be diseased forms[8] (“Involution-forms”).

Bacillus lacticus (Bacterium acidi lactici, Zopf) is always found in milk which has stood for some time, and in sour foods (cabbage, cucumbers, etc.); it turns the milk sour by producing lactic acid fermentation in the sugar contained in the milk; the lactic acid formed, eventually causes the coagulation of the casein. It resembles the Vinegar-bacteria, occurring as small cylindrical cells, rarely in short rows; not self-motile.—Several other Bacteria appear to act in the same way, some occurring in the mouth of human beings; some of these Bacteria give to butter its taste and flavour.

The kefir-grains which are added to milk for the preparation of kefir, contain in large numbers a Bacterium (Dispora caucasica) in the zooglœa-form, a Yeast-fungus, and Bacillus lacticus. Kefir is a somewhat alcoholic sour milk, rich in carbonic acid; it is a beverage manufactured by the inhabitants of the Caucasus, from the milk of cows, goats, or sheep, and is sometimes used as a medicine. In the production of kefir, lactic acid fermentation takes place in one part of the sugar contained in the milk, and alcoholic fermentation in another part, and the casein which had become curdled is partially liquefied (peptonised) by an enzyme of a Zooglœa-bacterium.

Bacillus amylobacter (Bacillus butyricus), the Butyric-acid-bacterium (Fig. [29]), is a very common anaerobic which produces fermentation in sugar and lactic-acid salts, and whose principal product is butyric acid. It destroys articles of food and (together with other species) plays a part in the butyric acid fermentation which is necessary in the making of cheese; it is very active wherever portions of plants are decaying, in destroying the cellulose in the cell-walls of herbaceous plants, and is thus useful in the preparation of flax and hemp. The cells are self-motile, generally cylindrical, sometimes united into short rows; endosporous; the spore-forming cells swell, assume very different forms, and show granulose reaction. The germ-tube grows out in the direction of the long axis of the spore.

Bacillus subtilis, the Hay-bacillus, is developed in all decoctions of hay; a slender, aerobic, self-motile Bacillus; endosporous (aplanospores); the spore-wall ruptures transversely on germination.

Crenothrix kuehniana occurs in the springs of many baths, in wells, in water or drain-pipes.

Fig. 31.—Beggiatoa alba: a from a fluid containing abundance of sulphuretted hydrogen; b after lying 24 hours in a solution devoid of sulphuretted hydrogen; c after lying an additional 48 hours in a solution devoid of sulphuretted hydrogen, by this means the transverse walls and vacuoles have become visible.

Beggiatoa (parallel with the Blue-green Alga Oscillaria). Long filaments formed of cylindrical cells which are attached by one of the ends, but which are nearly always free when observed. The filaments, like those of Oscillaria, describe conical figures in their revolutions, the free filaments slide upwards and parallel with one another; sheaths are wanting; strongly refractive sulphur drops are found in the interior. The Beggiatoas are the most prevalent Sulphur-bacteria. They occur, very commonly in large numbers, wherever plant or animal remains are decaying in water in which sulphuretted hydrogen is being formed; thus, for example, B. alba (Fig. [31]) occurs frequently as a white covering or slimy film on mud containing organic remains. B. mirabilis is remarkable for its size and its strong peristaltic movements. The Sulphur-bacteria oxidize the sulphuretted hydrogen, and accumulate sulphur in the shape of small granules of soft amorphic sulphur, which in the living cell never passes over into the crystalline state. They next oxidize this sulphur into sulphuric acid, which is immediately rendered neutral by absorbed salts of calcium, and is given off in the form of a sulphate, thus CaCO₃ is principally changed into CaSO₄. In the absence of sulphur the nutritive processes are suspended, and consequently death occurs either sooner or later. The Sulphur-bacteria may exist and multiply in a fluid which only contains traces of organic matter, in which organisms devoid of chlorophyll are not able to exist. The Beggiatoas very frequently form white, bulky masses in sulphur wells and in salt water, the traces of organic material which the sulphur water contains proving sufficient for them. The cellulose-fermentation, to which the sulphur wells in all probability owe their origin, mainly procures them suitable conditions for existence. The CaCO₃ and H₂S, formed during the cellulose fermentation by the reduction of CaSO₄ is again changed into CaSO₄ and CO₂ by the Sulphur-bacteria (Winogradsky, 1887).—Other Sulphur-bacteria, the so-called purple Sulphur-bacteria, e.g. B. roseo-persicina, Spirillum sanguineum (Fig. [23]), Bacterium sulfuratum, etc., have their protoplasm mixed with a red colouring matter (bacterio-purpurin) which, like chlorophyll, has the power, in the presence of light, of giving off oxygen (as proved by T. W. Englemann, 1888, in oxygen-sensitive Bacteria). The three purple Sulphur-bacteria mentioned, are, according to Winogradsky, not pleomorphic kinds but embrace numerous species.

Many Spirilli (Spirillum tenue, S. undula, S. plicatile, and others) are found prevalent in decaying liquids.

Bacteria (especially Bacilli) are the cause of many substances emitting a foul odour, and of various changes in milk.

Parasitic Bacteria live in other living organisms; but the relation between “host” and parasite may vary in considerable degree. Some parasites do no injury to their host, others produce dangerous contagious diseases; some choose only a special kind as host, others again live equally well in many different ones. There are further specific and individual differences with regard to the predisposition of the host, and every individual has not the same receptivity at all times.

The harmless parasites of human beings. Several of the above mentioned saprophytes may also occur in the alimentary canal of human beings; e.g., the Hay-bacillus, the Butyric-acid-bacillus, etc.; but the gastric juice prevents the development of others, at all events in their vegetative condition. Sarcina ventriculi, “packet-bacterium,” is only known to occur in the stomach and intestines of human beings, and makes its appearance in certain diseases of the stomach (dilation of the stomach, etc.) in great numbers, without, however, being the cause of the disease. It occurs in somewhat cubical masses of roundish cells (Fig. [25]).

Less dangerous parasites. In the mouth, especially between and on the teeth, a great many Bacteria are to be found (more than fifty species are known), e.g. Leptothrix buccalis (long, brittle, very thin filaments which are united into bundles), Micrococci in large lumps, Spirochæte cohnii, etc. Some of them are known to be injurious, as they contribute in various ways to the decay of the teeth (caries dentium); a Micrococcus, for instance, forms lactic acid in materials containing sugar and starch, and the acid dissolves the lime salts in the external layers of the teeth: those parts of the teeth thus deprived of lime are attacked by other Bacteria, and become dissolved. Inflammation in the tissues at the root of a tooth, is probably produced by septic materials which have been formed by Bacteria in the root-canal.

Dangerous Parasites. In a large number of the infectious diseases of human beings and animals, it has been possible to prove that parasitic Bacteria have been the cause of the disease. Various pathogenic Bacteria of this nature, belonging to the coccus, rod, and spiral Bacteria groups, are mentioned in the following:—

Pathogenic Micrococci. Staphylococcus pyogenes aureus produces abscesses of various natures (boils, suppurative processes in internal organs). The same effects are produced by—

Streptococcus pyogenes, which is the most frequent cause of malignant puerperal fever; it is perhaps identical with—

Streptococcus erysipelatis, which is the cause of erysipelas in human beings.

Diplococcus pneumoniæ (A. Fränkel) is the cause of pneumonia, and of the epidemic cerebro-spinal meningitis.

Gonococcus (Neisser) is the cause of gonorrhea and inflammation of the eyes.

Pathogenic Rod-Bacteria. Bacterium choleræ gallinarum, an aerobic, facultative parasite which produces fowl-cholera among poultry; it is easily cultivated on various substrata as a saprophyte. The disease may be conveyed both through wounds and by food, and may also be communicated to mammals.

Bacillus anthracis, the Anthrax bacillus (Fig. [32]), chiefly attacks mammals, especially herbivorous animals (house mice, guinea-pigs, rabbits, sheep, cattle), in a less degree omnivorous animals (including human beings), and in a still less degree the Carnivores. Aerobic. Cylindrical cells, 3–4 times as long as broad, united into long rod-like bodies, which may elongate into long, bent, and twisted filaments. Not self-motile. Endosporous. Germination takes place without the throwing off of any spore-membrane (compare Hay-bacillus p. [37] which resembles it). Contagion may take place both by introduction into wounds, and from the mucous membrane of the intestines or lungs, both by vegetative cells and by spores; in intestinal anthrax, however, only by spores. The Bacillus multiplies as soon as it has entered the blood, and the anthrax disease commences. The Bacilli not only give off poison, but also deprive the blood of its oxygen. Vegetative cells only occur in living animals. This species is a facultative parasite which in the first stage is a saprophyte, and only in this condition forms spores.

Fig. 32.—Anthrax bacillus (Bacillus anthracis) with red (b) and white (a) blood-corpuscles.

Fig. 33.—Anthrax bacillus. The formation of the spores; magnified 450 times.

Bacillus tuberculosis produces tuberculosis in human beings, also in domestic animals (perlsucht). It is a distinct parasite, but may also live saprophytically. It is rod-formed, often slightly bent, and is recognised principally by its action with stains (when stained with an alkaline solution of methyl-blue or carbolic fuchsin, it retains the colour for a long time even in solutions of mineral acids, in contrast with the majority of well-known Bacteria): it probably forms spores which are able to resist heat, dryness, etc.

Bacillus lepræ produces leprosy; Bacillus mallei produces glanders; Bacillus tetani, tetanus (the tetanus bacillus is very common in soil; anaerobic); Bacillus diphtheriæ, diphtheria; Bacillus typhosus, typhoid fever, etc.

Pathogenic Spiral Bacteria. Spirochæte obermeieri (Fig. [24]) produces intermittent fever (febris recurrens); it makes its appearance in the blood during the attacks of fever, but it is not to be found during intervals when there is no fever. Obligate parasite.

Spirillum choleræ asiaticæ (Microspira comma) without doubt produces Asiatic cholera; an exceedingly motile spirillum, which is also found in short, bent rods (known as the “Comma-bacillus”), it lives in the intestines of those attacked by the disease, and gives off a strong poison which enters the body. It is easily cultivated as a saprophyte.

A great many circumstances seem to show that a number of other infectious diseases (syphilis, small-pox, scarlet-fever, measles, yellow-fever, etc.) owe their origin to parasitic Bacteria, but this has not been proved with certainty in all cases.

It has been possible by means of special cultivations (ample supply of oxygen, high temperature, antiseptic materials) to produce from the parasitic Bacteria described above (e.g. the fowl-cholera and the anthrax Bacteria) physiological varieties which are distinct from those appearing in nature and possess a less degree of “virulence,” i.e. produce fever and less dangerous symptoms in those animals which are inoculated with them. The production of such physiological varieties has come to be of great practical importance from the fact that they are used as vaccines, i.e. these harmless species produce in the animals inoculated with them immunity from the malignant infectious Bacteria from which they were derived. This immunity is effected by the change of the products of one or more of the Bacteria, but we do not yet know anything about the way in which they act on the animal organism. The white blood corpuscles, according to the Metschnikoff, play the part of “Phagocytes” by absorbing and destroying the less virulent Bacteria which have entered the blood, and by so doing they are gradually enabled to overcome those of a more virulent nature.

Fig. 34.—a and b The same blood-cell of a Frog: a in the act of engulfing an anthrax-bacillus; b after an interval of a few minutes when the bacillus has been absorbed.

Class 5. Conjugatæ.

The Algæ belonging to this class have chlorophyll, and pyrenoids round which starch is formed. The cells divide only in one direction, they live solitarily, or united to form filaments which generally float freely (seldom attached). Swarm-cells are wanting. The fertilisation is isogamous (conjugation) and takes place by means of aplanogametes. The zygote, after a period of rest, produces, immediately on germination, one or more new vegetative individuals; sometimes akinetes or aplanospores are formed in addition. They only occur in fresh or slightly brackish water.

Order 1. Desmidiaceæ. The cells generally present markings on the outer wall, and are mostly divided into two symmetrical halves by a constriction in the middle, or there is at least a symmetrical division of the protoplasmic cell-contents. The cell-wall consists nearly always of two layers, the one overlapping the other (Fig. [35] C). The cells either live solitarily or are united into unbranched filaments. The mass of protoplasm formed by the fusion of the two conjugating cells becomes the zygote, which on germination produces one (or after division 2, 4 or 8) new vegetative individual. The chromatophores are either star-, plate-, or band-shaped, and regularly arranged round the long axis of the cell.

Fig. 35.—A Cell of Gymnozyga brebissonii, external view showing the distribution of the pores. B A portion of the membrane of Staurastrum bicorne with pores containing protoplasmic projections. C Cell-wall of Hyalotheca mucosa during cell-division: the central part, being already formed, shows the connection with the divisional wall.

The Desmidiaceæ are not able to swim independently, many species, however, show movements of different kinds by rising and sliding forward on the substratum. These movements, which are partly dependent upon, and partly independent of light and the force of gravitation, are connected with the protrusion of a mucilaginous stalk. The mucilage, which sometimes surrounds the whole individual, may acquire a prismatic structure, it is secreted by the protoplasmic threads which project through certain pores definitely situated in the walls (Fig. [35] A, B).

Vegetative multiplication takes places by division. A good example of this is found in Cosmarium botrytis (Fig. [36] A-D). The nucleus and chromatophores divide, and simultaneously the central indentation becomes deeper, the outer wall is then ruptured making a circular aperture through which the inner wall protrudes forming a short, cylindrical canal between the two halves to which it is attached (Fig. [36] C). After elongation the canal is divided by a central transverse wall, which commences as a ring round its inner surface and gradually forms a complete septum. The dividing wall gradually splits, and the two individuals separate from each other, each one having an old and a new half. The two daughter-cells bulge out, receive a supply of contents from the parent-cells, and gradually attain their mature size and development (Fig. [36] B-D). Exceptions to this occur in some forms.

Fig. 36.—Cosmarium botrytis. A-D Different stages of cell-division.

Fig. 37.—Cosmarium meneghinii: a-c same individual seen from the side, from the end, and from the edge; d-f stages of conjugation; g-i germination of the zygote.

Conjugation takes place in the simplest way in Mesotænium, where the two conjugating cells unite by a short tube (conjugation-canal), which is not developed at any particular point. The aplanogametes merge together after the dissolution of the dividing wall, like two drops of water, almost without any trace of preceding contraction, so that the cell-wall of the zygote generally lies in close contact with the conjugating cells. The conjugating cells in the others lie either transversely (e.g. Cosmarium, Fig. [37] d; Staurastrum, etc.), or parallel to one another (e.g. Penium, Closterium, etc.), and emit a short conjugation-canal (Fig. [37] d) from the centre of that side of each cell which is turned towards the other one. These canals touch, become spherical, and on the absorption of the dividing wall the aplanogametes coalesce in the swollen conjugation-canal (Fig. [37] e), which is often surrounded by a mucilaginous envelope. The zygote, which is often spherical, is surrounded by a thick cell-wall, consisting of three layers; the outermost of these sometimes bears thorn-like projections, which in some species are simple (Fig. [37] f), in others branched or variously marked; in some, however, it remains always smooth (e.g. Tetmemorus, Desmidium). Deviation from this mode of conjugation may occur within certain genera (e.g. Closterium, Penium). Upon germination the contents of the zygote emerge, surrounded by the innermost layers of the wall (Fig. [37] g, h) and generally divide into two parts which develop into two new individuals, placed transversely to each other (Fig. [37] i); these may have a somewhat more simple marking than is generally possessed by the species.

Fig. 38.—Desmidiaceæ. A Closterium moniliferum; B Penium crassiusculum; C Micrasterias truncata (front and end view); D Euastrum elegans; E Staurastrum muticum (end view).

The most frequent genera are:—

A. Solitary cells: Mesotænium, Penium (Fig. [38] B), Cylindrocystis, Euastrum (Fig. [38] D), Micrasterias (Fig. [38] C), Cosmarium (Fig. [36], [37]), Xanthidium, Staurastrum (Fig. [38] E), Pleurotænium, Docidium, Tetmemorus, Closterium (Fig. [38] A), Spirotænia.

B. Cells united into filaments: Sphærozosma, Desmidium, Hyalotheca, Gymnozyga, Ancylonema, Gonatozygon.

Order 2. Zygnemaceæ. Cell-wall without markings. The cells are cylindrical, not constricted in the centre, and (generally) united into simple, unbranched filaments. The whole contents of the conjugating cells take part in the formation of the zygote, which on germination grows out directly into a new filament.

Spirogyra is easily recognised by its spiral chlorophyll band; Zygnema has two star-like chromatophores in each cell (Fig. [40]); both these genera are very common Algæ in ponds and ditches.

Fig. 39.—Spirogyra longata. A At the commencement of conjugation, the conjugation-canals begin to protrude at a and touch one another at b; the spiral chlorophyll band and cell-nuclei (k) are shown. B A more advanced stage of conjugation; a, a’ the rounded female and male aplanogametes: in b’ the male aplanogamete is going over to and uniting with the female aplanogamete (b).

Fig. 40.—A cell of Zygnema. S Pyrenoid.