Cambridge Biological Series THE BRITISH FRESHWATER A L G >£ CAMBRIDGE BIOLOGICAL SERIES. GENERAL EDITOR : — ARTHUR E. SHIPLEY, M.A., F.R.S. FELLOW AND TUTOR OF CHRIST'S COLLEGE, CAMBRIDGE. THE BRITISH FRESHWATER ALG^E HonDon: C. J. CLAY AND SONS, CAMBRIDGE UNIVERSITY PRESS WAREHOUSE, AVE MARIA LANE, (Slaagoto: 50, WELLINGTON STREET. S.etp>i8: F. A. BROCKHAUS. gorfc: THE MACMILLAN COMPANY. ani Calcutta: MACMILLAN AND CO., LTD. [All Rights reserved.] A" • Plankton from Lough Neagh, Ireland ( x 100). 4 • K • Plankton from Loch Ruar, Sutherland (xlOO). A TREATISE ON THE BRITISH FRESHWATER BY G. S. WEST, M.A., A.R.C.S., F.L.S., PROFESSOR OF NATURAL HISTORY AT THE ROYAL AGRICULTURAL COLLEGE, CIRENCESTER ; FORMERLY SCHOLAR AND HUTCH1NSON RESEARCH STUDENT OF ST JOHN'S COLLEGE, CAMBRIDGE. ERRATA. 3, line 19, for Glaucocystidae read Glaucocystideae. 14, last line, after Zygnemaceje insert a semicolon. 165, line 12, for E. ansatum Ehrenb. read E. ansatum Kalfs. 304, line 1, for Cymatopleura Turpin 1827, read Cymatopleura W. Sm. 1851. 358 (Index), for Dabarya read Debarya. AT THE UNIVERSITY PRESS 1904 . A TREATISE ON THE BRITISH FRESHWATER BY G. S. WEST, M.A., A.R.C.S., F.L.S., PROFESSOR OF NATURAL HISTORY AT THE ROYAL AGRICULTURAL COLLEGE, CIRENCESTER ; FORMERLY SCHOLAR AND HUTCH1NSON RESEARCH STUDENT OF ST JOHN'S COLLEGE, CAMBRIDGE. CAMBRIDGE AT THE UNIVERSITY PRESS 1904 Catnftri&ge : PRINTED BY J. AND C. F. CLAY, AT THE UNIVERSITY PRESS. PREFACE. T^HE object of the present volume is to give the student a concise account of the structure, habits and life-histories of Freshwater Algae, and also to enable him to place within the prescribed limits of a genus any Alga he may find in the fresh waters of the British Islands. Although it may seem incongruous to treat of freshwater Algae apart from marine ones, there are many excuses for the production of a special treatise on the freshwater forms. Few genera of Algae, and still fewer species, exist both in salt and fresh water, and the vast majority of marine Algae are very different in nature from those inhabiting fresh water. The need for a book of this kind is very great, owing to the rapid strides made in the investigation of this class of plants during the last twenty years. To identify even many of the commonest of freshwater Algae one has at present to be fully conversant with most of the recent phycological literature, and I have endeavoured in this volume to give a general account of those facts concerning the British species which will be of most assistance to a diligent student. Many facts and suggestions concerning the life-histories, de- velopment, and relationships of freshwater Algae are here brought forward for the first time, and with few exceptions the figures are original, pains having been taken to state as far as possible the localities from which the specimens were collected. The figures are careful and accurate drawings to scale, and they are in no way diagrammatic. A few stages in the life-histories of various Algae, and certain figures showing structural peculiarities, have been copied from the original drawings of other authors, but in each case this has been specially mentioned. vi Preface The magnifications given under the figures are far from uni- form, but this is no great disadvantage, as a knowledge of the relative sizes of these plants is very soon acquired, and ' size ' is of no generic and little specific value. Accurate measurements are given of the most abundant and widely distributed species. It was originally my intention to add a chapter on the Peri- dinieae, but after further consideration I have for two reasons excluded them. Lack of space would have compelled me to have given a very indifferent account of them, and I also prefer to regard them as a group quite distinct from the Algas. Most zoologists claim these organisms as Dinoflagellates, and the Peri- diniese of this country are sufficiently numerous and important to require separate treatment. Similar remarks apply to the Characese. They are best re- garded as distinct from the Algae, as their vegetative organs exhibit far more differentiation than the vegetative structures of any of the freshwater Algae, and their sexual reproduction is of a distinctly higher type. In some instances I have quoted freely from previous publi- cations of my own, sometimes with slight alterations. The work was undertaken at the request of Mr A. E. Shipley, to whom I tender my best thanks for assistance and advice during its publication. I have also to thank Mr Edwin Wilson for the care he has expended in reproducing the drawings. I take this opportunity to remark that a good systematic text- book of British Freshwater Algaa, with descriptions of all the known species, remarks on their affinities, and if possible, with figures, is at the present time very urgently needed. There is, in fact, no single book, or set of accessible books, by means of which a student can hope to accurately identify one-third of the freshwater Algse he may find in a single day's ramble through a reasonably productive part of the country. I venture to state that this is the only branch of systematic botany in which such a state of affairs exists. The reason for it is not far to seek. It is one result of the general neglect of systematic botany (especially Cryptogamic) in the botanical laboratories of this country. Every encouragement Preface vii has been given, and is given, to students to take up physiological botany or to investigate the morphology of such plants as exhibit sufficiently striking peculiarities to arrest the attention even of a casual observer ; but what encouragement is given to a student who wishes to take up the systematics of any group of plants ? The answer is found in the ' Bibliography ' of every work on systematic botany. Although the work of the systematist is indispensable to a laboratory worthy of the name, there is undoubtedly in many quarters a lack of appreciation of systematic work, because it is at the same time the most laborious and the most vexatious of any form of biological investigation. It is becoming more and more difficult every day to conduct systematic investigation away from the special libraries indispensable to every well-equipped laboratory, and unless a slight encouragement is given to the laboratory student to take up some branch of systematic botany this department of botanical science will be left largely in the hands of the foreigner. One cannot emphasize too much the importance of a sound knowledge of the geographical distribution of some of the more lowly types of Cryptogams, particularly of the Desmidiaceae. Such a knowledge, which can only be acquired by the patient labours of the systematist, will throw much light on one of the most interesting of all problems concerned with the later phases of the earth's history, namely, the land-connections of previous periods. The frontispiece consists of a reproduction of two photo- micrographs to show some of the characters of the freshwater plankton. One is a photograph of some material collected from Loch Ruar, Sutherland, by Mr J. Murray, of the Scottish Lake Survey (Pullar Trust). The other represents plankton of a somewhat different nature from Lough Neagh, Ireland. G. S. WEST. ClRENCESTER, April 7th, 1904. TABLE OF CONTENTS. INTRODUCTION. PAGE Books relating to British Freshwater Algae 1 Occurrence, collection, and preservation of Freshwater Algae . . 3 Cultivation of Algae 9 ALG.E. Algae : what they are, and the six classes into which they are divided 10 Structure of Freshwater Algae 11 Vegetative multiplication 13 Asexual reproduction 14 Sexual reproduction 15 Polymorphism ........... 18 Phylogeny and classification 21 Class 1. RHODOPHYCE^E, p. 34. Order I. NEMALIONACE^ 36 Family 1. Helminthocladieae 36 Batrachospermum, Chautransia, Thorea Family 2. Lemaneaceae 40 Lemanea, Sacheria Order II. CRYPTONEMIACE^ 43 Family 1. Squamariaceae 43 Hildenbrandtia Class 2. PH^EOPHYCE^E, p. 44. Order I. SYNGENETICLE 44 Family 1. Hydruracese 45 Hydrurus Family 2. Chrysomonadinacese 46 Synura, Syncrypta, Uroglena Family 3. Dinobryaceae 47 Dinobryon Family 4. Phseocapsacese 48 Phseococcus, Pbseosphsera, Sticbogloea Class 3. CHLOROPHYCE^E, p. 50. Order I. (EDOGONIALES 57 Family 1. (Edogoniaceae 57 (Edogonium, Bulbochsete Order II. CILETOPHORALES 66 Family 1. Coleochaetaceae 67 Coleocbaete Family 2. Herposteiracese 70 Herposteiron •Family 3. Ulotrichaceae 73 Ulotbrix, Hormospora, Gloeotila, Geminella, Radio- filum, Stichococcus, Uronema, Binuclearia Family 4. Cylindrocapsacese 81 Cylindrocapsa Family 5. Chsetophoracese 83 Cbaetophora, Myxonema, Draparnaldia, Pseudochsete, Tha mniochsete Family 6. Microthamniaceae 89 Microthamnion, Gongrosira, Leptosira Family 7. Trentepohliacese 93 Trentepohlia Order III. ULVALES 95 Family 1. Ulvacese 95 Monostroma, Enteromorpha Order IV. SCHIZOGONIALES 98 Family l. Prasiolaceae 98 Prasiola Contents xi PAGE Order V. MICROSPORALES 100 Family 1. Microsporaceae 100 Microspora Order VI. CLADOPHORALES 101 family 1. Cladophoraceae 102 Chaetomorpha, Rhizoclonium, Cladophora, Chaetonella Family 2. Pithophoraceae 106 Pithophora Family 3. Sphaeropleaceae 107 Sphseroplea Order VII. SIPHONED 108 Family I. Vaucheriaceae 109 Vaucheria Order VIII. CONJUGATE 114 Family 1. Zygnemaceae 116 Sub-family I. MESOCARPE^E 117 Mougeotia, Gonatonema Sub-family II. ZYGNEME^E 123 Debarya, Zygnema, Spirogyra, Choaspis Family 2. Desmidiacese 135 Sub-family I. SACCODERM^E 152 Tribe 1. Gonatozygce . , . . . . . 152 Gonatozygon, Genicularia Tribe 2. Spirotceniece . . . . . . . 154 Spirotsenia, Mesotsenium, Cyliudrocystis, Netrium Sub-family II. PLACODERM^E 156 Tribe 3. Peniece 157 Penium Tribe 4. Closteriece ....... Iu7 Roya, Closterium Tribe 5. Cosmariece 161 Docidium, Pleurotsenium, Tetmemorus, Euastrum, Micrasterias, Cosmarium, Xanthidium, Arthro- desmus, Staurastrum, Cosmocladium, Oocardium, Sphserozosma, Onychonema, Spondylosium, Hya- lotheca, Desmidiurn, Gymnozyga Order IX. PROTOCOCCOIDE^ 178 Family 1. Chaetopeltidese 180 Chaetopeltis, Chsetosphseridium, Conochsete, Poly- chsetophora xii Contents PAGE Family 2. Volvocaceae 184 Sub-family I. CHLAMYDOMONADE^E 186 Carteria, Chlamydomonas, Chlorogonium, Sphaerella Sub-family II. PHACOTEA; 189 Phacotus Sub-family III. VOLVOCE^E 190 Gonium, Stephauosphsera, Pandorina, Eudorina, Volvox Family 3. Endosphaeraceae 197 Chlorochytrium, Centrosphsera, Phyllobium Family 4. Characieae 199 Characium Family 5. Pleurococcaceae . . . . . . . 201 Pleurococcus, Trochiscia, Radiococcus, Protoderma, Hor- motila, Urococcus Family 6. Hydrodictyacese 206 Sub-family I. HYDRODICTYE^E 207 Hydrodictyon Sub-family II. PEDIASTRE^E 209 Pediastrum, Euastropsis Family 7. Protococcaceae (or Autosporaceae) . . . 212 Sub-family I. CCELASTRE.E ' 213 Coelastrum, Sorastrum Sub-family II. CRUCIGENIE^E 215 Crucigenia, Tetrastrum Sub-family III. SELENASTRE^E 217 Dactylococcus, Scenedesmus, Dimorphococcus, Ankistro- desmus, Closteriopsis, Actinastrum, Selenastrum, Kirchneriella Subfamily IV. OOCYSTIDE^E 226 Oocystis, Nephrocytium, Eremosphsera, Palmellococcus, Chlorella Sub-family V. TETRAEDRIE^E 231 Tetraedron, Cerasterias Subfamily VI. PHYTHELIE^: 232 Golenkiriia, Richteriella, Lagerheimia, Chodatella Sub-family VII. DICTYOSPH^ERIE^E 235 Dictyosphaerium, Dictyocystis, Tetracoccus, Botryococ- cus, Ineffigiata Contents xiii PAGE Family 8. Palmellaceae 239 Sub-family I. PALMELLE^E . . . . . 240 Palmella, Palmodactylon, Schizochlamys, Sphserocystis Sub-family II. TETRASPORE^E 243 Tetraspora, Apiocystis Sub-family III. GL(EOCYSTIDE,E 244 Glceocystis, Dactylothece, Palmodictyon, Botrydina Class 4. HETEROKONT.E, p. 248. Order I. CONFERVALES 249 Family 1. Chlorotlieciaceae 250 Stipitococcus, Characiopsis, Miscbococcus, Oodesmus Family 2. Tribonemaceae 253 Cblorobotrys, Ophiocytium, Tribonema, Bumilleria Family 3. Botrydiaceae 258 Botrydium Class 5. BACILLARIE^E, p. 260. Order I. CENTRIC^ 273 Sub-order 1. DISCOIDE.E .274 Family 1. Melosiracese 274 Melosira Family 2. Coscinodiscaceae 276 Cyclotella, Stephanodiscus, Coscinodiscus Sub-order 2. SOLENOIDE^E 277 Family 1. Rhizosoleniaceae • 278 Rbizosolenia, Cylindrotheca Order II. PENNATJ5 279 Sub-order 1. FRAGILARIOIDE^ 280 Family 1. Tabellariaceae . . . . . . • 281 Tetracyclus, Tabellaria, Diatomella, Denticula Family 2. Meridionacea 283 Meridion Family 3. Diatomacese . 284 Diatoma Family 4. Fragilariaceae 285 Fragilaria, Synedra, Asterionella Family 5. Eunotiaceae 287 Ceratoneis, Eunotia xiv Contents PAGE Sub-order 2. ACHNANTHOIDE^E 289 Family 1. Achnanthacese 289 Achnanthes Family 2. Cocconeidaceae 290 Cocconeis Sub-order 3. NAVICULOIDE^E '291 Family 1. Naviculacese 291 Navicula, Stauroneis, Vanheurckia, Amphipleura, Gyro- sigma, Amphiprora, Mastogloia Family 2. Gomphonemacese 297 Gomphonema, Rhoicosphenia Family 3. Cocconemaceae 298 Cocconema, Amphora, Epithemia Sub-order 4. NITZSCHIOIDE^E . . .. . . . 301 Family 1. Nitzschiaceae 301 Bacillaria, Nitzschia, Hantzschia Sub-order 5. SURIRELLOIDEJE .'..... 303 Family 1. Surirellacese 303 Cymatopleura, Surirella, Campylodiscus Class 6. MYXOPHYCE^E, p. 306. Sub-class 1. GLAUCOCYSTIDEJE 316 Family 1. Glaucocystacese 317 Glaucocystis, Chroothece Sub-class 2. ARCHIPLASTIDE^E 317 Order I. HORMOGONE^E 318 Sub-order 1. PSILONEMATE^E 319 Family 1. Stigonemacese . . . - . . . . 319 Stigonema, Hapalosiphon Family 2. Scytonemaceae 322 Microchaete, Scytonema, Tolypothrix, Desmonema, Diplo- colon Family 3. Nostocacese 324 Nostoc, Anabsena, Aphanizomenon, Nodularia, Cylindro- spermum Contents xv PAGE Family 4. Oscillatoriacese 329 Sub-family I. VAGINARIE.E 330 Schizothrix, Dasyglcea, Microcoleus Sub-family IT. LYNGBYE^E 332 Plectonema, Symploca, Lyngbya, Phormidium, Oscil- latoria, Arthrospira, Spirulina Sub-order 2. TRICHOPHORE^ 337 Family 1. Rivulariaceae 337 Amphithrix, Calothrix, Dichothrix, Rivularia, Gloeo- trichia Family 2. Camptotrichaceae 341 Amrnatoidea Order II. COCCOGONEJE 342 Family 1. Chamaesiphoniacese . . . . . . 342 Chamaesiphon Family 2. Chroococcaceae 343 Sub-family I. CHROOCYSTE^E 344 Gloeochsete Sub-family II. CHROOCOCCE^E 345 Glceothece, Aphanothece, Synechococcus, Dactylococ- copsis, Merismopedia, Tetrapedia, Coslosphaerium, Gomphosphseria, Microcystis, Gloeocapsa, Aphano- capsa, Porphyridium, Chroococcus INDEX . 353 Plankton from Lough Neagh and Loch Ruar .... Frontispiece INTRODUCTION. ONE of the earliest attempts to bring together all that was then known concerning British Freshwater Algae was Dillwyn's ' British Confervas,' which appeared in 1809, and hardly any further advance was made in Britain until the appearance in 1845 of Hassal's ' History of British Freshwater Algae.' About this time two very important works were commenced on the continent, one being Kiitzing's ' Tabulae Phycologicae,' the first part of which .appeared in 1846, and the other Rabenhorst's 'Flora Europgea Algarum,' issued from 1864-68. Ralfs' ' British Desmids ' appeared in 1848, and for the next thirty years Henfrey, Hicks and Archer were almost the sole contributors to the literature of British Fresh- water Algae, the publications of Archer being very numerous and most valuable. From 1882-84 Cooke issued his ' British Freshwater Algae ' and in 1887 Wolle's ' Freshwater Algae of the United States ' appeared. Since the publication of these two books more actual work has been accomplished in the investigation of freshwater Algae than at any previous period, particularly by continental investigators, amongst whom may be mentioned Wille, Wittrock, Nordstedt, Bornet, Thuret, Lagerheim, Klebs, Hansgirg, Schmidle, Chodat, Borge, Boergesen, Lemmermann, and others. In Britain, Marquand, Bennett, and Roy have done systematic work in certain districts, and, in conjunction with my father, I have myself spent much time in the investigation of the Algae of many parts of the British Islands. During this later period of approximately twenty years many new phases have been discovered in the life-histories of Algae, and much has been found out with regard to their habits and mode of life. In addition, a great deal has been accomplished in clearing up the synonymy of these plants, so that taking into consideration all these circumstances, it is now doubtful if thirty w. A. 1 2 Introduction per cent, of the British freshwater Algse could be identified with certainty from Cooke's book ; and Wolle's American publication would be of little or no assistance. The relationships and affinities of the Alga3 described in these publications, and in many cases their life-histories also, are now much better known. This has resulted in great changes in their classification. At the time Cooke's book was published it was expected by many that during the next few years the groups of the Protococcacese and ChroococcaceaB would have disappeared, and statements were made by certain authors advocating great polymorphism in Algae, evidence being brought forward to prove that many of the more lowly forms were obviously stages in the development of higher forms. I have elsewhere pointed out1 that these statements were based upon very inadequate observations and that more evidence is yet required concerning the life-histories of some of the lowly types before any definite statements can be formulated as to their systematic position. Again, because a few observers have at different times suggested and attempted to show that these lowly types are only developmental stages, that constitutes no reason why, when their life-histories are unknown, they should be neglected and left out of consideration. Yet, that is largely the case in Wolle's ' Freshwater Alga? of the United States.' Blackman2 in advocating the primitive nature of the genus Ghlamydomonas, also remarks that " this specific constancy of the most primitive type is in strong opposition to the idea of wide polymorphism brought forward by Hansgirg, Chodat, and Borzi, which associates different genera, and even members of different families, in the life-history of one individual." No one would doubt for a moment the existence of considerable polymorphism in most groups of the Alga?, but it is certainly on a more reason- able scale than was at one time advocated. The classification I have adopted is thoroughly explained in the next chapter and the reasons for so arranging these plants are stated in full. With regard to the terminology, I have for the most part followed that used by Vines in his ' Text-book of Botany3.' 1 G. S. West, 'Algafl. of Cambridgeshire,' Journ. Bot. 1899, pp. 52—53. 2 F. F. Blackman, 'The Primitive Algas and the Flagellata,' Ann. Bot. xiv, 1900, p. 660. 3 S. H. Vines, 'A Students' Text-book of Botany,' London, 1895. Introduction 3 Exception may be taken to the rejection of Cohn's group of the Schizophyta, which was instituted to include the Schizomycetes (or Bacteria) and the Schizophyceae (or Blue-green Algae). These two series of plants undoubtedly present a similarity in their method of multiplication by simple cell-fission, but it must be remembered that most unicellular and colonial Algae habitually multiply in this manner, and although the Bacteria stand near in this respect to some of the less differentiated Blue-green Algae, there are many reasons for not including the two series of organisms in the same group. The Blue-green Algae possess chlorophyll and phycocyanin disposed within the cells in the manner of a primitive chromatophore, and are thus capable of carbon-assimilation ; whereas in the Bacteria this is not the case. A ciliated motile condition is only known to occur in about two blue-green organisms, whereas that is the normal condition in most of the Bacteria ; and the spore-formation, with very few exceptions, is quite different in the two groups. The Myxophyceae are also of a much higher type of organization than the Bacteria, possessing a primitive nucleus (which in the Glaucocystidjk has become a true cell-nucleus) and a cell- wall composed partly (and in the case of certain cells, entirely) of cellulose. Moreover, the habits and mode of life of most of them are totally different from those exhibited by the Bacteria. In this volume the Blue-green Algae are placed in the class Myxophyceae (Stizenberger, I860)1, which is an earlier name than Phycochromophyceae (Rabenhorst, 1864) or Cyanophyceae (Sachs, 1874), the limits of which were carefully and exactly made out by Stizenberger. It is the name under which the Blue-green Algae have been placed by systematists for many years past, but for some unaccountable reason it has not up to the present been even mentioned in general text-books on botany. OCCURRENCE, COLLECTION, AND PRESERVATION OF FRESHWATER ALG^E. Algae are universal in their occurrence, no moist situation being without some type of Alga. They are found on damp earth, rocks, walls, palings, tree-trunks, in rain-tubs, etc. ; they are met with in all kinds of running water, from the torrent, waterfall and cataract 1 Stizenberger in Rabenhorst's Algen Sachsens systematisch geordnet, 1860, p. 17. 1—2 4 Introduction to the slowest river. They are most abundant, however, in still waters, occurring in quantity in pools, ditches and lakes. They occur either floating at the surface, being simply immersed in the water, or attached to submerged stones, or to larger aquatic plants as epiphytes, etc. The larger Algae are often conspicuous as green slimy masses forming a surface coat to ponds, ditches, etc., or attached as large green masses to the rocks and stones of rivers. Rocks over which the water is constantly dripping possess at times quite a characteristic Alga-flora, and many of the more uncommon Algae are found in such situations. If such rocks present vertical wet faces, they are often covered with thick leathery patches, or gelatinous masses, which exhibit a great variety of colour. This material is always of interest and usually consists of a mixture of plants belonging to the blue-green Algae or Myxophyceae. Some Algae have acquired a symbiotic relationship with other plants, and even with animals. -One species of Anabcena lives symbiotically with the aquatic bycopod Azolla, and another with the Hepatic Blasia, and some Algae belonging to the genus Chlorella are connected symbiotically with such animals as Hydra viridis and certain small species of Amoeba, Paramecium, Ophrydium, etc. Again, there is the Lichen, which is a compound organism consisting of a Fungus associated symbiotically with Algae of the genera Plearococcus, Trentepohlia, Cephaleuros, Nostoc, Stigonema, Scytonema, etc. The genus Foreliella has a symbiotic relationship to the freshwater mussel (Anodonta) and several other Algae are similarly related to sponges. Many of the most beautiful Algae are exceedingly minute and occur in quantity in situations which are not at first obvious, and which are only found by experience. They occur embedded in a thin mucus surrounding the stems and leaves of submerged plants, such as Utricularia, Myriophyllum, Nymphcea, Nuphar, Potamo- geton, Scirpus fluitans, Isoetes, etc. Many of the submerged mosses, such as Sphagnum contortum, 8. plumosum, Amblystegium scorpi- oides, A. falcatum, A. exannulatum, A. glaucum, Fontinalis anti- pyretica, Jungermannia inflata, Nardia emarginata, etc., are often richly covered with these minute Algae. Numerous minute Algae occur along with an abundance of the Peridinieae and Copepoda scattered through the surface waters of lakes, rivers, and other large bodies of fresh water, and constitute a large proportion of the Freshwater Plankton. The animal and Introduction 5 vegetable organisms occurring in the plankton form the food of most of the smaller aquatic animals, and so, indirectly, form the basis of the food-material of lacustrine and river fishes. Little is known concerning the food-value of the freshwater plankton, but statistics of this nature have been very carefully compiled with regard to the Baltic Sea. Brandt1 states that the chemical com- position of the plankton of this sea in autumn and winter is intermediate between that of " rich pasturage " and green lupines. The proportion of fat is greater than in land products used as fodder, but in spring the great abundance of Diatoms causes such a great increase in the amount of ash as to preclude direct com- parison with land plants. Many of the Algas found in the plankton are more or less characteristic, some of them being largely and others entirely surface organisms. The majority of them belong to the Palmellaceae, Protococcaceae, Volvocaceae, Desrnidiaceae and Bacillariese. Most of the Desmids of the plankton possess very long spines or processes which terminate in spines, and in those species which normally possess long spines the latter are of greater length when the plants occur in the plankton than when found in other situations. Some of the Protococcacese and Diatoms have also acquired long spines. The assumption of this spined con- dition is to be correlated with their free-floating existence and their consequent need for greater protection against those animals of the plankton which feed on Algae2. Algae exist under very varied conditions of temperature. In temperate and arctic climates many of them can survive prolonged freezing even when in the ordinary vegetative condition. It is quite possible to melt out from the ice numerous healthy Alga3 which have suffered in no way from their exposure to such a low temperature. In the arctic and antarctic regions, in the Alps and in the Andes, there is a gjio^-flora. consisting principally of Algae which pass their entire existence on the snow and ice. This collection of Algae, which is known as the ' Cryoplankton,' consists of a few forms which are more or less universal in such situations3. 1 Brandt in Wissensch. Meeresimtersuchungen, N. Folge, Bd iii, Heft 2, 1898 ; consult also American Naturalist, xxxii, Dec. 1898. 2 West & G. S. West, 'Scott. Freshw. Plankton,' Journ. Linn. Soc. Bot. xxxv, Nov. 1903, p. 554. 3 The most interesting of these Algae are Sphcerella nivalis Sommerfeldt (the Eed Snow plant) and a Desmid, Ancylonema Nordenskioldii, first discovered byBerggren in the snows of Greenland, and afterwards by Lagerheim in the Andes and by Chodat on Mont Blanc. 6 Introduction Algae also occur in warm streams, and the vegetation of hot-springs consists exclusively of Algae. They can exist in hot water and hot vapour up to a temperature of 94'5° C. (200° F.)1. It is worthy of note that the Algae which occur at very high altitudes, and which therefore exist at relatively low temperatures, and those which inhabit the hottest springs, are, with few exceptions, species of Myxophyceae and Bacillarieae. Some Algae become encrusted with carbonate of lime or with silica, and play no small part in the formation of the deposits which are generally found in the neighbourhood of hot-springs. The comparative richness of any district in freshwater Algae depends very largely on its physical geography and on the geo- logical formations. Mountainous tracts are more prolific than flat districts, even though many of the larger Algae are absent from them. Most of the larger filamentous Algae and an abundance of the commoner unicellular forms are found in low-lying quiet waters, but in mountainous areas the filamentous forms are chiefly representatives of the Myxophyceae and Conjugatae, the presence of numerous species of the genus Mougeotia being a marked feature of such districts, and the unicellular forms are greatly increased by the addition of numerous Desmids. If the mountains consist of the Older Palaeozoic rocks, of Pre-Cambrian rocks, or of rocks of Igneous origin, there is a surprising numerical increase, not merely of species but also of individuals ; and in comparison, a mountainous district of carboniferous limestone or other formation is distinctly poor. Thus, the English Lake District, Wales, and certain parts of Scotland and Ireland yield a much greater variety of Algae than any other parts of the British Isles. The poorest area of all is the fen district in the east of England. The most prolific localities in the British Islands, and perhaps in the whole of Europe, for freshwater Algae are the small tarns and peat-bogs which lie in the hollows of the Lewisian gneiss of north-west Scotland. The plankton of the larger lakes of this area is also much richer in the Desmidiaceae than any which has been described from elsewhere. Most of the unicellular Algae and some of the filamentous ones, unless specially protected as in many Desmids, are readily taken 1 W. H. Brewer in Amer. Journ. Science, ser. 2, xli. These Algae were unicells, filamentous Algae. having been observed up to a temperature of 85° C. (185°F.); G. S. West in Journ. Bot. 1902, p. 241. Introduction 7 as food by Amoebae, Turbellarians, Oligochaetes, Tardigrades and Crustacea. The tadpoles of the common frog feed almost exclu- sively on the larger filamentous Algae, and Bles has recently shown that the larvae of that most remarkable African frog, Xenopus Icevis, feed exclusively on the lower Algae1. A considerable pro- portion of the food of freshwater Lamellibranchs also consists of living and decaying Algae. For the collection of freshwater Algae a plentiful supply of small wide-mouthed tubes or bottles will be found most useful. Small quantities of the larger, strictly aquatic Algae should be put into these tubes, care being taken not to overstock the tube. A small tuft of the Alga with plenty of water is best, and the tube should not be filled more than three-quarters full. The reason for this is obvious, as rapid decomposition accompanies overcrowding, and it frequently happens that collections cannot be examined for many hours after they have been made, or under certain circum- stances even for a day or two. To collect the minute Algae that occur attached to larger water plants, the latter should be removed from the water with as little mud as possible, the superfluous water allowed to drain away for a few minutes, and they should then be gently squeezed over a wide- mouthed bottle, the issuing water being collected in the bottle. In the sediment which settles to the bottom of the water in the bottle will be found numerous unicellular and other small Algae. Sometimes a hundred or even two hundred species may be obtained from a small quantity of such material. The Algae of the plankton are collected from the surface layers of water by means of silken tow-nets. If it is desired to keep the plants living for some time they should be placed in wide-mouthed jars with an abundance of water, and not exposed to too strong light. Sterile species of the Zygnemaceae and (Edogoniaceae will often become fertile under these conditions. 1 There can be little doubt that a portion of the food of Ceratodus, the Australian mud-fish, consists of Algse. An examination of the intestine of this fish (for which I must express my indebtedness to Prof. Howes), revealed masses of sticks, twigs, leaves, fragments of Hepatics, etc., all of which would have been taken in by the fish from the muddy bottom of the water in which it lived. This material would be mostly in a dead condition before being swallowed and it seems to suffer little change in its passage through the gut ; but a microscopical examination shows amongst it the decomposed remains of many kinds of Algae, including thousands of the empty valves of Diatoms. 8 Introduction Algae should always be examined in the living state whenever possible, as some of them are more easily determined when alive. Many of the Desmidiaceae and Bacillariese, however, especially those with characteristic surface markings, can only be determined with precision from the dead empty cells or semicells. In preserving Alg83 for future examination several fluids may be used. In studying the structure of the cell-contents a 2 — 4 °/0 formalin solution is best for subsequent staining, etc. This is almost equalled by a dilute solution of picric acid. But if only the cell-outlines and the structure of the cell-wall are required then there is no better preservative than a 4 °/0 solution of potas- sium acetate (containing a trace of copper acetate). An equal volume of this solution added to the water in which the Algse are living is quite sufficient. A very instructive paper has been published by Pfeiffer R. v. Wellheim1 on the methods of prepara- tion, staining, etc., of alg»3, in which chromacetic acid is largely recommended for preserving them. Certain reagents such as a solution of iodine, methylene blue, hsematoxylin, ammonia-car- mine, etc., are almost essential to all students of Algaa. A 2 °/0 cocaine solution is also very useful for the observation of the cilia of motile forms. Some Alga3 can be preserved by drying, either on paper or on slips of mica, but they are always better for purposes of future examination when preserved in a fluid medium than when dried. The only Algge that preserve well by drying are the Myxophyceaa. These Algse on soaking out again in water almost regain their original freshness, and, moreover, retain their original bright colours. Algse are best mounted in the fluid in which they have been preserved, and the best varnish with which to seal them up is gold-size. Everyone who has had any experience of fluid mounts, however, knows quite well that if his specimens keep for a long time it is due more to good fortune than to any other cause. Many fluid mounts, even the best ones, frequently begin to dry up by the formation of air-bubbles in the centre of the slide, which gradually extend towards the periphery. The only explanation of this is the porous nature of the thin coverslip. In examining Alga3, in following out their life-history, and in 1 F. Pfeiffer R. v. Wellheim, 'Preparation der Siisswasseralgen,' in Pringsheiin's Jahrbuch. fur wissensch. Botan. Bd xxvi, Heft 4, Berlin, 1894. Introduction 9 identifying them, they should always be carefully drawn to scale with the help of a Camera Lucida. This is the surest way of obtaining accurate measurements of the plants, and also much the best way of impressing on the memory their diagnostic features. Great attention should be paid by all students of Algae to their cytological characters, — the structure of the cell-wall, the disposi- tion of the protoplasmic cell-contents, the form and structure of the chromatophores, the presence or absence of pyrenoids, etc. It is the absence of any definite information on these points that renders many books on Algae almost useless. No student can acquire erroneous ideas of such common genera as Ulothrix, Tri- bonema (Conferva), Microspora, and others, if he has once realized their fundamental cytological characters. CULTIVATION OF ALG.E. It is often desirable to cultivate Algae in order to investigate their life-history and polymorphism. Under cultivation an Alga is often under abnormal conditions, and as a result, it sometimes develops strange forms which are quite unknown in the natural state of the plant. Careful observation of these cultures frequently affords good evidence towards the elucidation of the phylogenetic relationships of Algae. Cultures can be made at various tempera- tures, in water, in sugar solutions of various strengths, or if neces- sary under damp conditions only. Cultures are most frequently made in solutions of a nutritive character, but sometimes good results are obtained in pure water or in weak saline solutions. A medium containing gelose is very favourable for making pure cultures of the lower Algae1. Klebs and others have emphasized the usefulness of cultures on gelatine, agar-agar, and other solid media, and cultivation experiments on damp porcelain plates are frequently a success. The temperature necessary to obtain the best cultures varies with different types of Algae, but 20° C. is a good average temperature. 1 Chodat and Grintzesco in Arch. Sci. Phys. et Nat. x, 1900, p. 386. ALG^E. are Thallophytes of a simple or complex structure, and are of a green, yellow-green, blue-green, red or brown colour. Most of them live entirely submerged in water and the major portion of them inhabit the sea. They are found floating freely at the surface, attached to stones, or as in a large number of the fresh- water forms, adhering in gelatinous masses to the submerged portions of more highly organised aquatic plants. A few prefer damp situations in which they do not become immersed at all, or only periodically become covered with water. They are mainly distinguished from the Fungi by the presence of chlorophyll and consequently by their mode of life. Even in the red, brown, and blue-green Alga3 chlorophyll is present, but the green colour is masked by the presence of other colouring- matters. As the colouring-matter is usually the same throughout large groups of these plants which agree in other characters, particularly in the method of reproduction, they are classified as follows : — Class 1. Rhodophycece (or the Red Algae), containing a reddish colouring-matter known as phycoerythrin. Mostly marine. Class 2. Phceophycece (or the Brown Algae), containing a brown colouring-matter known as phycophasin. Mostly marine. Class 3. Chlorophycece (or the Green Alga3), containing only the green colouring-matter known as chloro- phyll. Very largely freshwater plants. The stored product of assimilation is in almost all cases starch. Freshwater Algce 11 Class 4. Heterokontce (or the Yellow-green Algae), contain- ing a large proportion of a yellow pigment known as xanthophyll. The stored product of assimila- tion is a fatty substance. Freshwater. Class 5. Bacillariece (or the Diatoms), containing a brown colouring-matter diatomin, which much resembles the phycophaein of the brown Algae. Universal both in fresh and salt water. Class 6. Myxophycece (or the Blue-green Algae), containing a blue colouring-matter known as phycocyanin. The stored product of assimilation is most probably glycogen. Mostly freshwater. By far the greater part of the vegetation of the sea consists of marine Algae, and with few exceptions these marine forms are of quite a different nature from the freshwater ones. It is only with freshwater Algae that this volume is concerned. Certain Algae are known in a fossil state. These are mostly Diatoms, the siliceous valves of which are eminently suited for fossilization, and a few others in which the thallus was encrusted with carbonate of lime. The majority of other Algae are of much too fragile and delicate a nature to become fossilized, and most of the records of such fossil Algae are of very doubtful value. Freshwater Algae exhibit a variety of types of structure. Some of them are unicellular, each plant consisting of a single protoplasmic unit or energid (i.e. a mass of protoplasm containing a single nucleus) surrounded and enclosed by a definite cell-wall (e.g. Desmidiaceae, Bacillarieae, and many Protococcoideae) ; others are unseptate or cosnocytic plants composed of an aggregate of protoplasmic units enclosed within a common cell-wall (e.g. Sipho- neae, Hydrodictyon) ; others are incompletely septate plants, each segment containing a number of protoplasmic units within a cell- wall, the septation of the plant going on independently of the divisions of the nuclei (e.g. Cladophorales) ; others are multi- cellular or completely septate plants, each segment containing one protoplasmic unit (e.g. Zygnemaceae, Chaetophorales, etc.). Many of the unicellular forms are solitary cells, but others occur as colonies, in which the individual cells are more or less loosely held together in a common mucilaginous envelope, which is either secreted by the protoplasm of the cells or is derived from 12 Algce the cell-walls. This mucilaginous sheath is present in most of the unicellular and filamentous freshwater Algae, and sometimes attains a huge development. Its nature was well investigated by Haupt- fleisch1 and more recently by Schroder2. The multicellular forms consist of closely connected cells form- ing a thallus, which exhibits a great variety of form. It may be spherical (e.g. Ccelastrum), filamentous (e.g. Spirogyra, Ulothrix, etc.), or a flattened expansion (e.g. some species of Coleochcete, Protoderma). Sometimes the thallus is differentiated into a " root " and a thalloid " shoot " (e.g. Botrydium, Rkizoclonium, (Edogonium, Spirogyra, etc.3), but the " root " is in all cases merely an organ of attachment and is more correctly called a hapteron. The cell-wall always consists largely of cellulose, and is some- times delicate, sometimes of considerable thickness and strength, being cuticularized or even silicified, but it is rarely, if ever, lignified. It often becomes gelatinous in its outer layers. The principal colouring-matter of the cell is usually arranged in definite parts of the protoplasm known as chromatophores. A single cell may contain one or many chromatophores. If the chromatophores contain the green colouring-matter chlorophyll, they are known as chloroplastids (or chloroplasts) ; if they contain some other colouring-matter they are termed chromoplastids (or chromoplasts). Plastids are present in all groups of Algse, but those present in the Myxophyceae are of a very primitive character. Chromatophores, particularly chloroplasts, often contain pyrenoids, which consist of colourless masses of proteid substance. The central mass of the pyrenoid is a proteid substance of crystalloidal character which bears a great resemblance to an aleuron grain. It is sometimes angular, sometimes rounded, or it may be quite irregular in its outward form, and is often surrounded by an amylaceous envelope or coat of starch. The latter sometimes becomes lobed and penetrates into the chromatophore to such an extent that its existence appears doubtful. In Spirogyra the envelope of amylaceous material round each central mass (or pyrenocrystal) is in the form of a number of grains of starch. On 1 Hauptfleisch, ' Zellmeinbran und Hiillgallerte der Desmidiaceen,' Mitteil. aus d. Naturwiss. Vereine f. Neuvorpommern und Riigen, 1888. 2 Schroder, ' Untersuchungen iiber Gallertbildungen der Algen,' Verhand. des Naturhist.-Med. Vereins zu Heidelberg, Bd vii, Heft 2, 1902. 3 Borge, ' Ueber die Ehizoidenbildung,' Upsala nya Tidnings Akteb. Tr. 1894 ; West and G. S. West in Ann. Bot. vol. xii, March 1898. Vegetative multiplication 13 the division of a cell the pyrenoids usually divide equally. Some- times a pyrenoid in a well-nourished cell multiplies by division without any division of the cell or the cell-nucleus. In a badly nourished cell, the amylaceous portion first disappears and then the crystalloidal part. The pyrenoid is thus a store of reserve food-material, and it may arise quite spontaneously without the previous existence of pyrenoids in the cell. Almost all Algae are holophytes ; that is to say, they are them- selves able to elaborate organic material from the mineral and other inorganic substances found in the water, or in some instances, in the atmosphere, in which they exist. The chlorophyll found in the chromatophores of the cells arrests certain rays of light, the energy of which is utilized by the living protoplasm for the con- struction of organic substance from the inorganic materials taken up. Algae absorb a relatively large amount of mineral food sub- stances, particularly nitrates, from the water in which they live. It has been assumed that the presence of nitrates in abundance is necessary for the prolific growth of Algae, but it is certainly true that these plants occur in quantity in water which is relatively poor in nitrates. Whipple and Parker1 state, as a result of experi- ments on the occurrence of small chlorophyll-bearing organisms in the waters of lakes, that the presence or absence of carbonic acid is one of the fundamental factors which influence the growth of Algae. The tropical Algae of the genera Phyllosiphon and Cephaleuros are partial parasites, and a few have already been mentioned as symbiotic with other plants or even with animals. The growth of the thallus may be apical or intercalary. In many Algae it is by the repeated division of a single apical cell, or by a series of marginal cells, as in the expanded thallus of Coleo- chcete. In many of the filamentous Algae with intercalary growth all the cells of the thallus are meristematic and undergo division (e.g. Zygnemaceae, Ulotrichaceae). Vegetative multiplication occurs in the unicellular forms by ordinary cell-division or fission, and in many of these plants it is the only method of increase. The division may take place in one direction only (e.g. Aphanothece, Glosothece, Stichococcus), in two directions in one plane (e.g. Tetraspora, Merismopedia), or in all directions of space (e.g. Gloeocystis, Gloeocapsa, and many others). 1 Whipple and Parker, in Trans. Amer. Micr. Soc. May 1902. 14 Alga3 In the Desmidiaceae, in which the cells generally exhibit a more or less deep median constriction, division is only in one direction, and it is brought about by the development of two new half-cells (or semicells) between the old halves. So that each of the indi- viduals formed after one division consists of an old and a new half-cell. In many unicells the division is accomplished by the formation of daughter-cells within the mother-cell. The daughter- cells are rejuvenized and metamorphosed portions of the original mother-cell and are enclosed in the old wall of the mother-cell. Sometimes the daughter-cells are set free by the bursting of the wall of the mother-cell, but it often happens that the old wall of the mother-cell swells up and remains as an outer, wider coat to the daughter-cells. Successive generations of cells are produced in the same manner inside the enlarged walls of the mother-cells until quite a colony is formed inside the swollen cell-wall of the original mother-cell (e.g. many Protococcoideae and Chroococcaceae). In many types of lower Algae there is no definite line to be drawn between this so-called free cell-formation and the ordinary vege- tative division1. In certain of the Protococcaceae two or four daughter-cells arise in a mother-cell, and at the time of their escape from the parent-cell they possess the exact form and external peculiarities of the parent ; these have been termed autospores. Increase of cells occurs in the filamentous Algae by new divisions, the septa being always transverse to the length. In the GEdogoniaceae the method of cell-division is somewhat specialized and a description of it is given under the family. On injury to the filamentous coenocytic Algae septa usually appear cutting off the injured part. The injured portion soon dies away, and if it happens to be in the median part of a filament, two filaments are thus set free. This occurs frequently in Vaucheria, and if the injuries to one filament are numerous, all the injured parts are sometimes cut off, the intermediate uninjured portions developing into new filaments on being set free. The reproduction of freshwater Algae is brought about in a great variety of ways, most of the plants exhibiting both an asexual and a sexual mode of reproduction. Asexual reproduction. — In some cases special non-motile cells develop into cysts or unicellular gemmae (e.g. Zygnemaceae? 1 Chodat in Ann. Bot. 1897, p. 102. Asexual reproduction 15 they are also specially cut off in the Vaucheriaceae), and in the filamentous Myxophyceae hormogones or multicellular gemmae are formed. Sometimes single non-motile cells are produced, which have been termed by Wille akinetes when they are formed without rejuvenescence and aplanospores when formed by rejuvenescence (e.g. Chaetophorales, Confervales, Conjugate). Many of these non- motile asexual spores, which may be either akinetes or aplanospores, rest for considerable periods before germination and are known as hypnospores (or sometimes as hypnocysts). Asexual reproductive organs are known as gonidangia when borne on the gametophyte generation and sporangia when borne on the sporophyte. A sporangium (or a gonidangium) as a rule gives origin to a number of spores (or gonidia), but in Vaucheria, (Edogonium, and some of the Ulotrichaceae only one gonidium is formed in the gonid- angium. Very often the gonidia consist of motile cells which receive the name of zoogonidia (or zoospores). One of the most frequent methods of asexual reproduction is by means of zoogonidia, which are found in all groups of freshwater Algae except the Conjugates (the largest order of the Chlorophyceae), the Myxophyceae, and the Bacillarieae (or Diatoms). Zoogonidia are small masses of proto- plasm formed singly by the rejuvenescence of the entire contents of a cell, or more frequently in numbers by free cell-formation. They are not possessed of a cellulose wall, but are furnished with one (?), two, four, or many cilia, with one or more chromatophores, and often with one or two contractile vacuoles. The cilia are usually disposed towards one end or one side of the zoogonidium and their rapid vibratile movements cause it to swim quickly through the water. A red or brown pigment-spot is very often present. After a time the zoogonidium comes to rest, the cilia disappear, the protoplasm secretes a cellulose wall, and the zoo- gonidium develops into a new plant. Sexual reproduction. — Reproduction by the union of male and female elements, or gametes, is fairly general throughout the Algae, but it is entirely absent in the Myxophyceae, in some of the unicellular Protococcoideae, and in the Syngeneticae. Sometimes the gametes are clearly differentiated into male and female ele- ments, but in other cases sexual differences are scarcely appreciable. The following is a summary of the sexual methods of reproduction met with in the freshwater Algae : — 16 Algce I. Sexual reproduction by isogamous gametes (isogametes), or precisely similar sexual cells which undergo the process of con- jugation. a. Gametes ciliated, known as planogametes or zoogametes, set free, and on conjugation forming a zygospore (or zygote) (e.g. Ulotrichacese, Ulvaceae, Trentepohliaceae, Pandorina). « b. Gametes not ciliated, known as aplanogametes. i. Conjugation forming a zygospore which after a period of rest develops directly into a new gametophyte (e.g. Bacillariese and Desmidiacese, in which the gametes are set free; Zygnemeas, in which the gametes are not set free). ii. Conjugation forming a zygospore which immediately develops a rudimentary sporophyte with one spore (e.g. Mesocarpese). II. Sexual reproduction by heterogamous gametes (hetero- gametes), or clearly differentiated sexual cells which undergo the process of fertilization. a. Oogamous heterogamy : — The female organ is an oogonium containing an oosphere. The male organ is an antheri- dium in which are developed motile, ciliated antherozoids (or spermatozoids). The result of fertilization is the production of an oospore (e.g. VaucheriaceaB, (Edogo- niales, certain of the Chaetophorales and Cladophorales, and some of the Volvocacese). b. Carpogamous heterogamy: — The female organ is &procarp (consisting of carpogonium and trichogyne) with no specially differentiated female cell. The male cells are non-ciliated spermatia (or pollinoids). Fertilization results in the development of a cystocarp (or sporocarp) with contained spores known as carpospores (e.g. RhodophyceaB). The sexual organs of those Algse with similar sexual cells are termed gametangia. If the Algae are unicellular then the cell itself becomes the gametangium (e.g. Desmidiacese, Bacillarieaa), and in the multicellular and coenocytic forms the ordinary vegeta- tive cells become the gametangia (e.g. Zygnemaceae, Chaetophorales, Sexual organs 17 Hydrodictyon}. In the whole of the Conjugate the gametangium gives origin to only one aplanogamete, but in other Algae it is more usual for several gametes to arise from one gametangium. Planogametes, such as are found in the UlotrichaceaB, are pear- shaped bodies with the chromatophores more or less confined towards the broader end, the narrower end being colourless. Two cilia are inserted at or near the narrow, colourless end, and a red pigment-spot is frequently present. They exhibit active move- ments for a longer or shorter period of time and finally conjugate, each pair coming into contact by their colourless poles. In those Algae with dissimilar sexual cells the female organ consists either of a single cell or a coenocyte known as the oogonium, which is usually more or less spherical (e.g. (Edogoniacese), some- times attenuated into a beak (e.g. Vaucheria}, or produced at the apex into a long, narrow tube, the trichogyne (e.g. Coleochaetaceae). An oogonium usually contains a single female cell or oosphere (e.g. Vaucheriacese, (Edogoniaceae), but sometimes there are many oospheres present (e.g. Sphseropleaceae). An oosphere is generally a spherical cell containing chromatophores, and often with a clear, colourless area at one side known as the receptive spot. It is at this spot that the antherozoid enters during the process of fertilization. In the Rhodophyceae the female organ is usually a multicellular structure (in the freshwater Red Algae it is unicellular) termed a procarp, which is divisible into two portions, a carpogonium and a trichogyne. The male organ is known as the antheridium. It is usually unicellular, but in (Edogonium it may consist of one or of many cells. Each antheridial cell often gives rise to quite a number of male cells (spermatozoids or anther o z oids), but in the (EdogoniaceaB it gives rise to two, and in the ColeochaetaceaB and most of the Rhodophyceae to only one. Antherozoids frequently resemble the asexual zoogonidia, but are usually smaller. They are commonly pear-shaped, but may be elongate and almost rod-like. They possess two cilia which are generally inserted at the pointed end, but laterally in Volvox, Vaucheria, etc., and in (Edogonium there is quite a tuft of cilia at the narrower end. They are as a rule faintly coloured and often possess a red pigment-spot. Sexual organs have not been observed in many of the Pro- tococcoideae and in the Syngeneticae, and are apparently entirely absent from the whole class of the Myxophyceae. w. A. 2 18 Algce Many Algae exhibit an alternation of generations in their life- history. In those forms in which neither asexual nor sexual reproduction is known this alternation of generations is, of course, absent. Other Algae exhibit slight indications of an alternation of generations. Thus, in a large number of the Chlorophyceae, the sporophyte generation is represented by the zygospore. This zygospore can be described as a unicellular sporangium which often gives rise to two or four zoospores. Each zoospore, on coming to rest, germinates and produces the gametophyte generation. In the Mesocarpeae the isogamous gametes conjugate in a connecting- tube between the gametangia, and the zygospore immediately produces a rudimentary sporocarp consisting of a variable number of cells, one cell of which is the carpospore. This is the sporophyte generation. The carpospore, after a period of rest, germinates and gives rise to the new gametophyte generation. In the Rhodo- phyceae there is a well-marked alternation of generations. In the Algae the gametophyte is the important generation ; in fact, the 'plant ' is the gametophyte ; but as one proceeds higher in the scale of vegetable life there is a great reduction of the gametophyte accompanied by a corresponding increase in the development of the sporophyte, until in the Phanerogams the sporo- phyte becomes the 'plant' and the gametophyte is parasitic on it. POLYMORPHISM. Polymorphism occurs in most families of Algae. All those Algae which exhibit an alternation of generations are polymorphic, and some species appear to possess several different vegetative forms. It is very doubtful, however, if polymorphism occurs in Algae to the extraordinary extent advocated by some authors. Sirodot has proved the occurrence of several types of structure in the genera Batrachospermum and Lemanea, and it is fairly evident that the plants at one time described under the genera Prasiola, Schizo- gonium and Hormidium are different vegetative forms of one genus. Polymorphism is well illustrated in Botrydium, and numerous striking instances could be mentioned of other Algae in which it occurs, notably in the common genus Pleurococcus. Hansgirg, and following in his footsteps Wolle, have endeavoured to prove (on insufficient evidence) the existence of extraordinary polymorphism in Algae, relegating most of the unicellular Algae as Polymorphism 19 mere stages in the growth of higher forms. It is necessary, how- ever, to remark that a great many loose statements have been made on this subject, statements which are supported by no direct or conclusive evidence. Most of the remarks have been based upon the fact of the occurrence together, in one matrix, of various stages of different plants, and to the assumed identity of certain normally unicellular plants with unicellular stages in the life-history of higher organisms. Undoubtedly in the case of the Myxophycese many different forms are met with in one gelatinous matrix, and these are of the most confusing nature. Many of the higher blue- greeri Alga? do certainly pass through stages which resemble very much some of the so-called unicellular species, but there is equally no doubt that careful observation frequently proves that this is a resemblance and not an identity. In some instances it may be quite true that a blue-green form which has been accepted as a species in the past is really a stage in the development of another form, but that does not necessarily prove that every blue-green Alga exhibits wide polymorphism and that every form met with is only one stage in some complex life-history. Similarly, in the Chlorophycese, polymorphism is frequent, but because species of Chcetophora or Myxonema (Stigeoclonium) at one period of their existence regularly and normally break up into ' Palmel la-like ' forms, it does not follow that every aggregate of unicells such as Glceocystis, Palmella, etc., is merely a stage in the development of Chcetophora, Myxonema, or some other allied plant. The observation of the polymorphism of higher and lower types of Algae, both in nature and under cultivation, is, however, the surest and best way to discover their affinities, and in many cases furnishes direct evidence as to the phylogeny of the plants in question. Thus, the fact that Myxo- nema assumes under certain conditions a ' Palmella-st&te,' much resembling species of the genus Palmella but in no way specifically related to them, is one of the primary reasons for regarding Myxonema (and therefore the Ch^tophoracea?) as having been derived from the Palmellacese. Without question many of the Alga? referred to the order Protococcoideae have a much more direct relationship with fila- mentous green Alga?, particularly with the Chaetophorales, than is indicated by their present systematic position. . As an instance, the genus Stichococcus, described by Nageli as a unicell, un- doubtedly belongs to the family Ulotrichaceae and is connected by 2—2 20 Algce many intermediate stages with species of Kiitzing's genus Glceotila, and even with species of the genus Ulothrix. This was first definitely shown by Gay1 and afterwards emphasized by Klercker2. But, although in some instances this is the case, and various genera of the group ' Protococcoidese ' have to be transferred to other groups to which they more rightly belong, many forms still have to remain in the old group ' Protococcoidese ' until more is known concerning their life-histories and affinities. For instance, it has been asserted that species of the genus Tetraedron Kiitz. 1845 (= Polyedrium Nag. 1849) are merely stages in the develop- ment of Pediastrum, but this is now known to be erroneous3, and that even if certain forms are developed in the life-cycle of Pediastrum which much resemble species of Tetraedron, yet the latter genus is quite distinct and has a life-history of its own. It is, however, most probable that Pediastrum has been evolved from Algae of the nature of Tetraedron, and one of the connecting links has been discovered in a genus recently described by Lagerheim under the name of Euastropsis. As another example of erroneous conclusions arrived at from insufficient evidence, there is the case of the genus Chantransia. The discovery by Sirodot4 of the ' protonema-stage ' of Batracho- spermum was regarded by many people as a sufficient proof that species of Chantransia were merely asexual forms of Batracho- spermum. This was entirely due to the mistake of confounding the sporophytic shoots of Batrachospermum (and Lemanea) with certain true species of Chantransia which they much resembled. Murray5, in commenting upon this, says that to speak of the " Chantransia-foTms " of these genera " means no more than if the protonema of a moss were to be called its ' Conferva-form ' or the prothallus of a fern its ' Liverwort- form.' These growths of Lemanea and Batrachospermum have nothing to do with the valid generic type Chantransia." In conclusion, it seems well established that the higher types of Algae have originated by gradual evolution from the more lowly 1 Gay, ' Eecherches sur le developpement et la classification de quelques Algues Vertes,' Paris, 1891. 2 Klercker, ' Ueber zwei Wasserformen von Stichococcus,' Flora, 1896. 3 Cfr Lagerheim in Tromso Museums Aarshefter, 17. 1894. 4 Sirodot, ' Sur le developpement des Algues d'eau douce du genre Batracho- spermum,' Paris, 1875. 5 G. Murray, ' An Introduction to the Study of Seaweeds,' London, 1895, p. 208. Phylogeny 21 types, but the fact must not be overlooked that these lowly types, although they may have undergone many modifications, still persist, and great care should be taken not to confound them with those stages in the life-histories of the higher types which present so many resemblances to them. THE PHYLOGENY AND CLASSIFICATION OF THE FRESHWATER ALG.E. The researches and discoveries of the last few years have certainly thrown much light on the affinities of many genera and families of Algae, and constitute a very great advance in our knowledge of the phylogenetic relationships of these plants. It is by no means an easy task to give even a mere outline of the suggestions which have at different times been put forward as to the evolution of freshwater Algae, but one derives great assistance from two recently published papers, one by Chodat1 and the other by Blackman2, containing not only a summary of much of the work bearing on this difficult problem of phylogeny, but putting forward some well-founded suggestions as to the same. In the succeeding brief account of the evolution of freshwater Algae I have followed very largely the suggestions of Borzi, Blackman, Bohlin and others, with certain alterations based upon my own experience3. Taking first the Chlorophycese or green Algae, which a few years ago were in a chaotic condition, we find that this chaos has been greatly reduced to order and that the affinities of many of these plants have been clearly demonstrated. The four groups of the Confervoideae, Conjugates, Siphoneae and Protococcoidese, into which the green Algae have been usually classified, must be con- siderably modified in view of recent researches. The Conjugates and the Siphoneae will remain as distinct and natural orders of the green Algae, the former chiefly by reason of their reproduction and the latter on account of their coenocytic structure, but the Con- fervoideae and Protococcoideae were unquestionably unnatural 1 Chodat, 'On the Polymorphism of Green Algaa and the Principles of their Evolution,' Ann. Bot. xi, 1897. 2 F. F. Blackman, 'The Primitive Algne and the Flagellata. An Account of Modern Work bearing on the Evolution of the Algse,' Ann. Bot. xiv, 1900. 3 In 'Lectures on the Evolution of Plants' by D. H. Campbell (Macmillan Company, New York, 1889), there is a chapter on Algae (pp. 48 — 79) with a scheme of evolution (p. 79), but the latter appears to be largely based upon erroneous conceptions of the relationships of these plants. 22 Algce groups which could no longer be tolerated in the sense in which they were originally proposed. Chodat, from observations on the lower green Algae, both in a state of nature and in cultures, traces the principal groups of the Chlorophyceae back to the Palmellaceae, one of the lowly families of the order Protococcoidese. He recognizes three important tendencies which rule the lower green Algae : — (1) the zoospore-condition, the other two conditions being only transient ; (2) the sporangium-condition or unicellular motionless stage, the other conditions being realized accidentally; (3) the Tetraspora- stage, where non-motile cells are connected by regular cell-walls at right angles. Blackman follows somewhat on these lines, but he considers, along with others, that all the tendencies of the lower Alga3 have had an origin in the motile unicellular Chlamydomonads. Among the families of lower Algae constituting the group of the Proto- coccoideae, he observes three divergent vegetative tendencies: — • (1) a Volvocine tendency towards the aggregation of motile vegetative cells into gradually larger and more specialized motile true ccenobia : (2) a Tetrasporine tendency towards the formation of aggregations by the juxtaposition of the products of septate vegetative cell-division to form non-motile organisms of increasing definiteness and solidarity; (3) an Endosphaerine tendency towards the reduction of the vegetative division and septate cell-formation to a minimum. The simplest forms which exhibit any one of these three tendencies seem clearly to diverge from species of the genus Chlamydomonas, and these motile organisms must be regarded as the real primitive form of green plant and the foundation stone, so to speak, of the vegetable kingdom. Of late much work has been done at the germs Chlamydomonas by Goroschankin, France", Dill, Klebs, and Wille, and now the genus is brought into still more prominence. It has been found to contain some twenty-nine species which are remarkable for the constancy of their cytological characters. Unfavourable conditions produce in this genus the ' Palmella-condition.' This is the beginning of a vegetative non-motile existence such as predominates in the Palmellaceae. In the latter family the cells at intervals in their life-history escape from their walls, develop cilia, and return to the motile state as zoogonidia. Blackman remarks that the "formation of zoospores is then nothing but reversion to an ancestral type of Phylogeny 23 vegetative existence for a biological advantage, and all the vegetative existence of the higher Algas is phylogenetically a new intercalation into the life-history of the motile Chlamydomonad which is perma- nently in the zoospore condition, though walled, and in which zoospore-formation and vegetative cell-division are one and indistinguishably the same thing." Chlamydomonas itself has had an origin from the Proto- mastigina — one of the five subdivisions of the Flagellata proposed by Klebs — and two instances of the connecting forms are found in the organisms known as Polyblepharis Dang, and Chlorogonium Ehrenb. Many of these lowly Flagellates are green, but others are colourless saprophytic organisms, and in some either a saprophytic or holophytic nutrition may be carried on, depending on whether the organism is well fed or not1. In the same way that green organisms occur among the Flagellates so do colourless forms occur among the lower Algae. One species of Chlamydomonas — Chi. hyalina — is always colourless and saprophytic, and Dangeard's researches into Poiytoma have likewise shown that the small group of organisms of which Poiytoma uvella Ehrenb. is the best known representative should perhaps be regarded as a saprophytic sub-family of the Volvocace* which have probably evolved from a green organism of the Chlamydomonad-type. The various Flagellates such as Euglena and others belonging to the Eugle- noidina, have given origin to no organisms of preponderating plant-characters. The Volvocine tendency in the Chlamydomonad-type has caused the evolution of a series of organisms of gradually increasing complexity, which constitute the Volvocacese. These are genera which practically consist of coenobia of cells of the Chlamydomonad-type. The genus Gonium is perhaps very little removed from Chlamydomonas except in the possession of a four- celled or sixteen-celled colony. The highest development reached is the Volvox-colony, in which there are highly developed oospheres and antheridia. Between the isogamous Chlamydomonas or isogamous Gonium and the highly differentiated heterogamous condition of Volvox, there are two intermediate stages in Pandorina and Eudorina. The Tetrasporine tendency in the Chlamydomonad-type first resulted in the production of a series of forms in which vegetative 1 Zumstein in Pringsheim's Jahrbiich. fiir. wiss. Botan. xxiv, 1899. 24 cell-division gradually replaced the formation of zoogonidia as the chief method of multiplication. The first group of Algse evolved in this direction was the lowly family of the Palmellacese, in which the cells are grouped together either in all directions of space as in Palmella, or regularly disposed in one plane as in Tetraspora. The cells are enveloped in a general mucous envelope formed by the confluence of the special gelatinous cell-walls, and in every stage the cells on leaving the envelope are capable of swarming as zoogonidia. It is to this family of the Palmellacese that we must look for the origin of most of the other families of green Algae. The Endosphserine tendency in the Chlamydomonad-type has given rise to certain plants in which vegetative cell-division is absent, the multiplication of individuals taking place only by the formation of zoogonidia or gametes. These plants belong to the family Endosphseracese and are almost strictly unicellular. So far, then, the phylogeny of the green Algse can be illus- trated by the following simple diagram : — Volvocaceffl A Endosphaeraceae Palmellaceaa Chlamydomonas The Volvocine tendency has resulted in no higher development than the Volvox-co\ony, but a very reasonable suggestion has been made by Blackman as to the origin of the Siphonese by a further development of the Endosphserine tendency and formation of a thallus, which, although essentially coenocytic. is structurally uni- cellular and lacks the solidity acquired by septate cell-division. He remarks that " nothing appears to have been evolved from it of higher status than an Alga. While the Tetrasporine tendency has given rise to all the higher green plants, the Endosphserine Phytogeny 25 has only succeeded in producing the elaborate but puny mockery of them which we find in Caulerpa." It is now necessary to trace the further developments from the Palmellacese, which family was the first result of the influence of the Tetrasporine tendency on the Chlamydomonad-type. The Protococcacese is a group which has been gradually evolved from the Palmellacese by the direct production of the unicellular motionless stage with a firm cell-wall as the principal state of the plant, the zoogonidia and the Tetraspora-st&ge being only tran- sient conditions in the life-history, and often absent. In the lower forms of this family the cells are globose with firm cell-walls, and all their reproductive processes show a marked tendency to trans- form the motile elements into resting spores. In some of the other forms of the family the cells exhibit great variety of form (e.g. Oocystis, Nephrocytium, Kirchneriella, Chodatella, etc.), and reproduction is largely by a type of spore termed by Chodat an autospore. Such spores are usually produced in fours inside the mother-cell, and at the moment of their liberation they possess the exact form and external peculiarities of the mother-cell. Sometimes the autospores are quite free after their liberation (e.g. Lagerheimia, Oocystis), but at other times they are sur- rounded by a gelatinous envelope (e.g. Kirchneriella, Nephrocy- tium}. When the autospores are united together in a colony at the time of their expulsion an auto-colony is produced. Such is the usual method of multiplication of Scenedesmus. Forms of the nature of Ccelastrum and Sorastrum have originated from the lower Protococcacese with autospores, the latter being grouped together into a globular auto-colony. The position of the two genera Pediastrum and Hydrodictyon is still very doubtful. I am inclined to agree with Chodat that the resemblance is due to convergence rather than to a common origin. In Pediastrum the swarming stage is outside the mother- cell and the new cosnobium arises by the apposition of motile zoogonidia. In Hydrodictyon the new cosnobium also arises by the apposition of zoogonidia which have become quiescent, but is formed inside the mother-cell. Both genera consist of coenobia of coenocytes, and for the present they are best kept in the separate sub-families of the Pediastrea3 and Hydrodictyea3. Among the ChaBtophorales it is clear that the UlotrichaceaB have had a direct origin from the PalmellaceaB through such forms 26 Algce as Stichococcus, Hormospora, Radiofilum, Glceotila and GemineUat forms in which simple loosely connected series of cells occur em- bedded in a gelatinous envelope. The Chaetophoraceae are further specialized forms of the Ulo- trichaceae, which are distinguished mainly by their branched habit. The polymorphism exhibited by the Chaetophoracese, and the deve- lopment of zoogonidia and formation of resting-spores, also indicate a close connection with the Palmellaceae, but probably through the Ulotrichaceafi. Chodat considers the genus Pleurococcus as one type of the Chaetophoraceae which has been reduced owing to its existence as a lichen-gonidium, but this is a statement I cannot agree with. The Ulvales and the Schizogoniales are parallel groups, each of which has probably had a separate origin from the Proto- coccoideae. The Ulvaceae, especially such forms as Monostroma and Ulva, have most likely originated from Palmellaceous Algae of the nature of Tetraspora. The genus Microspora is difficult to relegate to its proper place in a classificatory scheme. It is the sole representative of the family Microsporaceae and its characters mark it off sharply from other green Algae. It may have originated from some aber- rant form of the Ulotrichaceae, but its affinities are at present doubtful. It is possible that the forms placed in the genus Rhizoclonium have originated from Microspora, and by a further specialization the genus Cladophora has been produced. The Cladophoraceae (and therefore the Pithophoraceae) may thus have had an origin from the Microsporacese. Bohlin1 has recently transferred the Cladophoraceae to the order Siphoneae owing to the ccenocytic nature of the segments of the thallus, but the validity of such a change is a question of opinion. Owing to the many points of resemblance between Hydrodictyon and Cladophora,, the former genus may possibly be a degenerate form of the Clado- phoraceae. Since 18972 I have regarded the Cladophoraceae as a distinct family of Chlorophyceae, in close proximity to the Siphoneae and far removed from the Ulotrichacese, yet I hardly see the justi- fication for its inclusion in the Siphoneae. I think it better to place the Cladophoraceae and Pithophoraceae, along with the Sphaeropleaceae, in a separate order, the Cladophorales. 1 Bohlin, 'Utkast till de Grona Algernas och Arkegoniaternaa Fylogeni,' Akad. Afhandl. Upsala, 1901. 2 W. & G. S. West in Journ. Boy. Micr. Soc. 1897, p. 475. Phylogeny 27 Luther and Bohlin have recently advocated considerable changes in the classification of the Green Algae, most of which have been rendered necessary by the abolition of the old artificial group of the ' Confervoideae.' I agree with Bohlin in the estab- lishment of the order ' Microsporales,' even though it appears to be giving undue prominence to a small group of more or less insignificant Algae, because species of the genus Microspora are referable to no other order of green Algae. Likewise, the CEdo- goniaceae require placing in a separate order because of their anomalous characters. Several of the recent students of freshwater Algae have attempted to show that all the main groups of the Chlorophycese have had a separate origin from unicellular, motile, ciliated or flagellated ancestors. This is no doubt a very helpful idea, but like many other such ideas it can easily be carried too far. It appears most probable that certain groups of green Algae have had a direct origin from ciliated or flagellated unicells, but that in itself is no proof that other groups have had a similar origin. There is not a shadow of evidence in support of the direct and individual origin of the Microsporaceae, the Conjugatse, the Vaucheriaceae, the (Edogoniaceae or the Cladophorales ; in fact, there is every reason to suppose that some at least of these groups have originated from previously existing filamentous forms. The origin of the Conjugatae seems very uncertain. Black- man, in his scheme of evolution1, and Bohlin2 have both suggested an origin from the unicellular motile Chlamydomonad-type, and therefore directly from the Flagellata. To my mind this shows a lack of experience of the Conjugatae as a whole, and particularly of the family Desmidiaceae. Whatever the true origin of the Conjugatae it cannot have been direct from Flagellate forms. Presumably the first Conjugates which would arise from such motile unicells would be themselves unicells, or loose aggregates of cells. Now, such is exactly the condition found in the Desmidiaceae ; but it has been clearly shown3 that the Desmidiaceae is unques- tionably a family of Conjugates derived by retrogression from filamentous ancestors, and therefore, they cannot by any possible means have had a direct origin from unicellular motile organisms. 1 Blackman, I.e. p. 684. - Bohlin, I.e. p. 22. 3 W. & G. S. West in Ann. Bot. xii, 1898, p. 55 ; G. S. West in Journ. Linn. Soc. Bot. xxxiv, 1899, pp. 409—415. 28 Algce It appears more probable that the early Conjugates were filamen- tous forms and that they originated from some other order of green Algae, corning to an abrupt conclusion soon afterwards. Nothing higher was evolved from them, but the group of the Desmidiacese became sharply marked off from the rest of the Conjugates owing to great specialization. The specializing ten- dency was in the direction of a remarkable increase in the com- plexity of morphological characters, and this was accompanied by degeneration of sexual differences. Perhaps there may be an affinity between certain of the Con- jugates and the genus Microspora, as the resemblance between such species as Microspora Lofgrenii Nordst.1 and Zygnema pachydermum West2 is most striking; the cell-walls are thick and exhibit the same structure, and in both plants precisely similar aplanospores are formed in identically the same manner. It is now necessary to consider a group of Algse for which Borzi* proposed the name of the ' Confervales.' In this order he included a number of Algse which had previously been scattered amongst various groups of the Chlorophycese. The characters of the group are based upon the structure of the cell, which contains parietal discoidal chromatophores of a yellowish-green colour and without pyrenoids. Even the zoogonidia possess discoidal chroma- tophores of a yellowish-green colour and two unequal cilia (some- times one ?). The plants may be unicellular, coenocytic or multi- cellular, and include amongst others the following genera : — Ophiocytium, Characiopsis, Ghlorothecium, Mischococcus, Tribonema (Conferva), Botrydiopsis and Botrydium. Bohlin4 in 1897 con- clusively demonstrated, by an exhaustive study of the structure of the cell-wall, the close affinity which exists between the genera Ophiocytium and Tribonema (Conferva); and, in addition, in the earlier stages of development these two genera, one of which is unicellular and the other multicellular, much resemble each other5. The order Confervales is subdivided into three families : — (1) Tri- bonemaceae, which includes Tribonema (Conferva), Ophiocytium, 1 Nordstedt in Botaniska Notiser, 1882, p. 55 ; W. & G. S. West in Journ. Bot. Febr. 1897, p. 34. 2 West in Journ. Linn. Soc. Bot. xxx, 1894, p. 266, t. xiii, f. 1—16. 3 Borzi in Boll, della Soc. ital. dei Microscop. i, 1889. 4 Bohlin in Bihang till K. Sv. Vet.-Akad. Handl. 1897, Bd xxiii, no. 3. 5 Bohlin I.e. t. ii, f. 47, 51, 52, 54—56; Wille in Ofvers. af K. Vet.-Akad. Forh. 1881, no. 8, t. ix, f. 15, 17, 18, 21—26; G. S. West in Journ. Bot. Mar. 1899, p. 106, t. 394, f. 18—22. Phylogeny 29 Bumilleria, Botrydiopsis, Chlorobotrys ; (2) Chlorotheciacece, which includes Mischococcus, Peroniella, Stipitococcus, Characiopsis, Chlorothecium ; (3) Botrydiaceae, including Botrydium. Now, amongst the Flagellate organisms there exists a genus described as Vacuolaria by Cienkowski1, which possesses yellow -green discoidal chromatophores without pyrenoids; and this organism, as in the case of the Chlamydomonad-type, may very possibly be the start- ing point of the Confervales. Lagerheim discovered another organism in 1897 which was further worked out by Bohlin2 and named Chloramoeba. It is of a similar type to Vacuolaria with discoidal chromatophores of a yellow-green colour, but more strictly a Flagellate. Great interest is likewise attached to the discovery by Luther3 in 1898 of yet another similar organism which he named Chlorosaccus. This organism has certain resem- blances to Tetraspora, but is of a yellow-green colour with several parietal disc-like chromatophores, and seems to connect Chlo- ramoeba and Vacuolaria with the direct line of descent of the Confervales. Luther proposed to remove all these forms out of the Chlorophyceae and suggested the name ' Heterokontce ' as a class equal with that of the Chlorophycese, and to include the Algal series ' Confervales ' and the corresponding Flagellate group ' Chloromonadina ' (or Chloromonadales). This class seems a very natural one and differs from the Chlorophycese in certain cy to- logical characters, such as the abundant presence of xanthophyll and the presence of a fatty substance as the stored product of carbon-assimilation. Bohlin has recently suggested that the Vaucheriacese should be included with the ' Confervales ' and ' Chloromonadales ' as one of the orders of the Heterokontae, with the name ' Vaucheriales.' There are, however, wide differences in structure between the Vaucheriacese and the Confervales, not to mention the absence of the yellow pigment and the highly differentiated sexual repro- duction present in the former ; neither is there any evidence that the plants of these orders are in any way phylogenetically related ; therefore, for the present, I prefer to retain the Vaucheriacese in the order Siphonese of the Green Algse. The origin of the Phseophycese, or Brown Algae, from brown 1 Cienkowski in Archiv. fur Mikroscop. Anat. vi, 1867. 2 Bohlin in Ofvers. af K. Vet.-Akad. Forh. 1897, no. 9. 3 Luther in Bihang till K. Sv. Vet.-Akad. Handl. Bd xxiv, 1898, no. 13. 30 Algce CO - 00-1 UOOX«;i-«JUHt? o — o en _ * * S 5"* IJUGATft. i xl |] f" "9 "s""T| o 1 1 i -J ^ 32l <-> i «< cb £3 yj k! LJ _ 8 o o ic: O Phylogeny 31 Flagellate organisms seems quite as reasonable as in the parallel case of the Green Algae. During recent years many genera of primitive brown Algae have been discovered, most of which appear to be intermediate forms between the higher brown Flagellates and the simpler types of filamentous brown Algae. The majority of these primitive brown Algae inhabit fresh water, but few of them have up to the present been observed in Britain. The Flagellate organism suggested as the possible starting point for this series is Chromulina Cienk.1, and the ascending series of forms include Phceocystis Lagerh., Phceosphcera West & G. S. West, Phceococcus Borzi, Entodesmis Borzi, Phceothamnion Lagerh. and Pleurocladia A. Br. Divergences along other lines from Chromulina may have given rise to the Hydruraceae, the Chrysomonadinaceae and the Dinobryaceae. Phceodactylon Bohlin and Stichogloea Chodat may have a relationship with the Phceococcus-type of brown Alga. PILEOPHYCE.E Pleurocladia PhsBothamnion Entodesmis Phaeococcus Phaeosphasra Hydruraceaa Pkseocystis Phaeodactylon Stichogloea Dinobryaceaa Chrysomonadaceaa Chromulina PKOTOMASTIGINA The origin of the Bacillarieae is still extremely doubtful, and no reasonable suggestions have yet been put forward as to their Cf. Lagerheim in Ofvers. af K. Vet.-Akad. Forh. 1896, no. 4, p. 288. 32 Algce line of descent. They are regarded by some as a group of the Phaeophyceae, but are better considered as a distinct class. It may be that there is a much more direct relationship between the Bacillarieae and the Flagellate Peridinieae than is at first apparent. The origin of the large class Rhodophyceae is still very un- certain, although quite recently a marine Flagellate with the chromatophores of the Rhodophyceae has been discovered by Karsten1. As there are so few freshwater representatives of this large class of Algae, a discussion as to their origin would here be out of place. So little is known concerning the Myxophyceae and their life- histories that any attempt to give an account of their origin and evolution would be mostly a matter of conjecture. It is interesting to note, however, the existence of blue-green motile organisms such as Cryptoglena Ehrenb. and Chroomonas Hansg.2 Reasons for retaining the word 'Myxophyceae' are stated in the Intro- duction (page 3). The classification commonly adopted at the present time is the one found in Engler and Prantl's ' Pflanzenfamilien,' in which the Green Algae were arranged by Wille, the Bacillarieae by Schiitt, and the Blue-green Algae by Kirchner. Wille followed Sachs in the removal of the Conjugatae from the Chlorophycese, but the reasons for this are certainly insufficient. It is also significant to note that since the publication of the classification referred to, Wille has regarded the Conjugatae as an order of Chlorophyceae3. The most recent classification of Green Algae in English is that put forward by Blackman and Tansley4 in the ' New Phytologist ' for 1902, and they not only accept at the outset the principal changes suggested by Luther and Bohlin, but carry them still further. They separate the CEdogoniales (as the "Stephanokontae") and the Conjugatae (as the "Akontae") from all the rest of the Chlorophyceae, which are placed under the "Isokontae." This arrangement is based upon the assumption that the CEdogoniales and the Conjugatae are phylogenetically independent of the " Isokontae," and that all three groups have arisen from the 1 Karsten in Wissensch. Meeresuntersuchungen, Kiel, Bd iii, Heft 2, 1898. 2 Hansgirg, ' Noch einmal iiber die Phykochromaceen-Schwarmer,' Bot. Cen- tralbl. Bd xxiv, 1885. 3 Wille, ' Algologische Notizen vn, vni,' Nyt Magazin f. Naturvidensk., B. 39, H. 1, Kristiania, 1901. 4 F. F. Blackman and A. G. Tansley, 'A Kevision of the Classification of the Green Algse,' The New Phytologist, 1902. Phylogeny 33 Flagellata. Be it remembered, however, that there is no direct evidence in support of the view that the CEdogoniales and Conjugates are phylogenetically independent of the rest of the Chlorophycese. Indeed, with regard to the Conjugates all the known facts concerning them tend to show that they, at least, have not had a direct origin from Flagellate ancestors. I have for many years made a special study of the Conjugate, including a particularly detailed investigation of the Desmidiacese, the family around which all the interest of this idea is centred; and I can say most emphatically that all the facts concerning these plants with which I am acquainted, far from supporting the idea of a Flagellate ancestry, tend to prove conclusively that this beautiful family of Conjugates has originated from filamentous ancestors. The separation of the Conjugate from the rest of the Chlorophycea? is therefore to my mind based upon an erroneous supposition, and there is likewise no evidence to show that the complete separation of the CEdogoniales from the rest of the green Alga3 is a just one. The Heterokontae is obviously a very natural class, but I have not transferred the Vaucheriacese to the Hetero- kontae nor the Cladophoracese to the Siphonese. The genus Prasiola has no relationship to the Ulotrichacese and I have placed it in the order Schizogoniales. My arrangement of the Conjugate is also quite different from that given by Blackman and Tansley, particularly in the family Desmidiacese, of which I have given a natural classification. In those facts lie the main differences between the classification put forward by Blackman and Tansley and the one used for the green Algae in the present volume, which is based upon a very extensive and careful study of these plants for many years. There will also be found many differences in the genera themselves and in their disposition, as I have arranged them in a manner which I consider to be much more in accordance with their affinities. For example, the genera Radiofilum Schmidle and Hormospora Breb. are undoubtedly feebly developed forms of the Ulotrichacese and have no place in the Protococcaceae; and the same is true of the genera Glceotila Kiitz. and Stichococcus Nag. Dactylothece Lagerh. is an elongated Glceocystis-\ike genus and has no relationship with either Dimorphococcus A. Br. or Scenedesmus Meyen ; and many other instances could be quoted. w. A. 3 Class 1. RHODOPHYCE^; (or Floridese). THIS class comprises the Algae usually known as the Red Seaweeds. They exhibit a variety of colours from bright red and purple to dark brownish-reds, brownish-green, blue-green and black. Very few of the genera are freshwater forms. The thallus is multicellular, very diverse in form, and consists of simple or branched cell-filaments which may be merely held in close proximity by mucilaginous material, or bound together by a tough intercellular substance, giving the thallus a parenchymatous appearance. The branching of the cell-filaments is very varied, the plants exhibiting many types of branching. The filaments increase in length by the repeated divisions of an apical cell. The cells are all protoplasmically continuous through pits in the transverse or cross-walls of the filaments. Each cell may contain one well differentiated nucleus, or more rarely the thallus may consist largely of coenocytes. The chromatophores are distinct and the chlorophyll is masked by either a red colouring-matter — phycoerythrin, or a blue colouring-matter — phycocyanin. Some- times pyrenoids are present. Asexual reproduction takes place by motionless spores known as tetraspores (or tetragonidia), which are generally bright red, and have neither cilia nor cell-wall. They are produced in a tetrasporangium (or tetragonidangium), usually in variously ar- ranged groups of four. This is the most common form of repro- duction. Zoogonidia are absent from the entire class. Sexual reproduction by male and female cells is wanting in some, but present in others. The female organ is a procarp which consists of a single cell containing a cell-nucleus, the carpogonium, drawn out into an attenuated, hair-like process called the trichogyne. The latter is homologous with the receptive spot Rhodophycew 35 of the oosphere of the green Algae. The male organ is an an- theridium of variable form which gives origin to large numbers of male cells. Each male cell opens at the apex and sets free a rounded, nucleated mass of protoplasm, without a cell-wall and without cilia, known as a spermatium (or pollinoid). Fertilization takes place by the attachment of the spermatium to the apex of the trichogyne and the union of their contents. As the nucleus of the spermatium disappears, it travels down the trichogyne and unites with that of the carpogonium, this fusion having been observed by Osterhaut in Batrachospermum JBoryanum1. The result of the fertilization of the carpogonium is the development of a fructification known as a cystocarp (or sporocarp), and the different groups of the Rhodophycese are characterized by the method of formation of this fructification. Sometimes the cystocarp is developed directly from the carpogonium ; but, fre- quently, the fertilizing influence is handed on to other cells in the neighbourhood of the carpogonium, and conjugation occurs between outgrowths of the fertilized carpogonium (known as 'ooblastema filaments) and certain auxiliary cells, the final result in all cases being the development of the cystocarp and the production of carpospores. Whatever be the method of formation of the cystocarp, the carpospores are always developed on a tuft of filaments which spring from fertilized cells and which are known as gonimoblasts. The class is subdivided into four orders : — Order I. Nemalionacece. This order includes four families, of which the Lemaneaceaa is exclusively fresh- water, and the Helminthocladiese includes several freshwater genera. Order II. Cryptonemiacece. One family of this order, the Squamariacese, contains a genus of which there are several freshwater species. Order III. Gigartinacece. Exclusively marine. Order IV. Rhodymeniacece. Exclusively marine. In addition to the four orders just enumerated, another group of Alga3 known as the Bangiacece is often included in the Rhodo- phyceae, but the systematic position of this group is very uncertain. 1 Osterhaut in Flora, Ixxxvii, 1900. ' 3—2 36 Rhodophycece The main argument for its inclusion in the Rhodophycese is derived from the red colour of the chromatophores, whereas the intercalary growth of the thallus and the absence of the pits between the thallus-cells are points against its inclusion among the Red Alga3. The so-called tetraspores of the Bangiaceae are somewhat remarkable, the whole of the contents of a thallus-cell going to form one unciliated, amoebiform spore. The sexual process is also of a very reduced type, far removed even from that of the simplest red Alga. The genus Bangia, which is a simple filamentous form, occurs on the shores of the British Islands and in the estuaries of the rivers, but it is not exactly a freshwater Alga. Order I. NEMALIONACEJE. The fertilized carpogonium gives origin directly to the gonimo- blasts, which are developed in tufts. Family 1. HELMINTHOCLADIE^E. The thallus is filamentous, simple or branched, with the secondary axes often arranged in whorls. The main axis may consist of a single row of cells, or of a central cell-filament surrounded by a cortical ring of smaller cell-filaments. The gonimoblast is a short tuft of cell-filaments and the terminal cells usually form the carpospores. When the terminal cell has shed its carpospore, the supporting cell grows through into the old cell- wall and produces a new spore-forming cell. There is no definite wall to the cystocarp. Genus Batrachospermum Roth, 1797. This is an exclusively freshwater genus with a wide distribution in temperate and tropical climates. Most of the species prefer deep water in which there is a slight current, but more rarely they are found attached to stones in fast streams. They scarcely ever occur in stagnant water, but are found frequently in bogs, usually at a point where a spring rises. The thallus, which is of a blue-green colour and enveloped in a thick coat of mucus, is remarkable for the great beauty and symmetry of its branching; sometimes it reaches a length of 16 — 20 cms. The plants are generally attached to Helminthodadiece 37 stones or wood by a number of thick old shoots ; these send off numerous primary axes which float freely in the water. The primary axis consists of a central filament of cells which grows by Fig. 1. A, Batrachospermum moniliforme Roth, from Malham Cove, W. Yorks. ( x 2) ; B — C, Batrachospermum vagum (Roth) Ag., from Thursley Common, Surrey; B ( x2); C, single node with lateral branches, more highly magnified. D, ger- minating spore. E, protonemal growth. F, Female organ and fertilization ; s, spermatium; c, carpogonium ; t, trichogyne. (D, E, and F after Schmidle. ) means of a hemispherical apical cell. The cells of this central filament become swollen at each end, a dense whorl of branches being produced at each swelling (or node). From the basal cells 38 Rhodophycece of the branches secondary branches grow downwards over the main axis, forming a cortical ring of cell-filaments (sometimes termed the pseudocortex). The apical cells of the lateral branches are frequently produced out into long hairs or bristles. The pro- carp is unicellular and is developed at the extremity of a small branch which stands out directly from the main axis, and which is termed by Sirodot the ' female axis.' The carpogonium possesses a short, straight, exposed trichogyne1, and after fertilization it develops the dense mass of gonimoblasts (frequently termed a ' glomerulus ') which constitute the cystocarp. The cystocarps are external, being developed amongst the dense whorls of branches, and the terminal cell of each gonimoblast produces a carpospore. On the development of the carpospores sporophytic shoots are formed which very much resemble species of the genus Chan- transia ; they are to be regarded as a kind of ' protonema,' which, under certain suitable conditions, develops into the sexual Batra- chospermum-p\a,nt. There are two more or less abundant species of the genus in the British Islands, B. inoniliforme Roth (Fig. 1 A) and B. vagum (Roth) Ag. (Fig. 1 B), each with a number of varieties. The latter is distinguished from the former by the more or less uniform development of the lateral branches along both the nodes and internodes of the inferior portions of the primary axis. A third species, B. atrum (Dillw.) Harv., with very short lateral branches and long internodes, is less widely distributed. Species of this genus commonly afford a home for epiphytes of the nature of certain species of Calothrix, Hapalosipkon, Ammatoidea, etc., and numerous Diatoms and Desmids are frequently present in their enveloping mucus. Genus Chantransia Fries, 1825. The plants belonging to this genus are much smaller than species of Batrachospermum and occur both in fresh water and in the sea. The freshwater species vary from about 3 to 7 mm. in length, and are usually found attached to rocks and stones in rapid rivers, cataracts and water- falls. The thallus consists of branched filaments of cells arising from a basal stratum, the apices of the branches being frequently . much attenuated and almost piliferous. In colour the plants are all shades of red, purple and blue. There is an entire absence of the mucous coat which is so conspicuous a feature of Batracho- spermum. It was thought for some time that all the species of 1 Schmidle, 'Einiges iiber die Befruchtung, Keimung, und Haarinsertion von Batrachospermum,' Bot. Zeitung, Heft 7, 1899. Helmmthocladie(v 39 Chantransia were merely non-sexual stages of Batrachospermum, and that under brighter condi- tions of light they underwent a metamorphosis, giving rise to the sexual stage or Batracho- spermum. The carpospores of the latter genus develop a pro- tonema-like growth which bears great resemblance to species of Chantransia, and many of these growths, both of Batrachosper- mum and Lemanea, have been erroneously described as species of that genus ; but, at the same time, these have nothing to do with the valid genus Chantransia. The sexual reproduction of Chan- transia has only been fully worked out in one species — Ch. corym- bifera Thur. On the fertilization of the carpogonium it develops numerous gonimoblasts upward- ly and on one side. There is thus formed a naked corymbose cysto- carp, the terminal cells of the gonimoblasts producing the car- pospores. The antheridia are likewise developed in clusters. Asexual reproduction occurs by tetraspores and also by other spores which remain undivided and are known as ' monospores.' These, on germination, divide into four cells in one plane, giving rise to the basal stratum from which the branched fila- ments spring. There are some seven or eight British freshwater species of the genus, of which Ch. pygmcea Kiitz. (fig. 2 A — C) and Ch. molacea Kiitz. are perhaps the most frequent. Fig. 2. A, Chantransia pygmaa Kiitz., from Penyghent, W. Yorks. ( x 100). B and C, branches of the same with 'monospores' (m) ( x 300). D, Ch. scotica Kiitz., from Cornwall; a small portion of the thallus showing the pits in the transverse walls ( x 400). 40 Rhodophycece Genus Thorea Bory, 1808. This is a rare genus with only one species — Th. ramosissima Bory — which, although found in several of the rivers of France and Germany, has only once been recorded for Britain (from Walton-on-Thames). It has a round filamentous thallus, which is much branched and reaches a length of 30 — 60 cms. It is about the thickness of a horse-hair, of a purple-brown or dark brown colour, and very mucous. There is a central solid axis consisting of filaments of cells, and arising from this axis are a very large number of short compact branches, which are slightly attenuated. The cells of the branches are from two to five times longer than their diameter. Schmidle1 has recently worked out much of its structure and fructification, and this has been largely confirmed by Hedgcock and Hunter2. This genus has been placed under the PhseophyceaB, but the pigment, the presence of starch-like granules in the cells, and the naked non-motile spores, indicate a near relationship with certain of the FlorideaB. Family 2. LEMANEACE^B. This is a small group of exclusively freshwater Algae including the two genera Lemanea and Sacheria. They are plants which only grow in rapid torrents, occurring attached to the rocks of waterfalls, to stones and wood in mill-sluices, etc., always where the force of the water is greatest. The thallus is composed of a basal, attached portion, termed by Sirodot3 a " systeme radicant," from which arise csespitose tufts of erect, branched, simple fila- ments reaching a length of 3 — 8 mm. From portions of these filaments the fructiferous branches arise. These are the most conspicuous and important parts of the plant, in most species the vegetative portion dying away after their production, and in a short time they become fixed by organs of attachment of their own. Each species is thus represented by two distinct sets of indi- viduals, the one vegetative and the other reproductive. The fructiferous branches are elongated, thread-like portions 1 Schmidle, ' Untersuchungen iiber Thorea ramosissima Bory,' Hedwigia, Bd xxxv, 1896. 2 G. G. Hedgcock and A. A. Hunter in Botan. Gazette, xxxviii, 1899. 3 Sirodot, 'Etude anatomique, organogenique, et physiologique de la Fam. des Lemaneacees,' Ann. Sci. Nat. Bot. torn, xvi, Paris, 1872. I Lemaneacetv 41 of the phallus, of a cartilaginous consistency, and hang freely in the rapid torrent. They are of an olive-green or greenish-black colour and grow to a length of 15 — 18 cms. At short, more or Fig. 3. A, Sacheria mamillosa Sirodot (nat. size), from E. Wharfe, W. Yorks. B, portion slightly magnified showing antheridial areas. C, Lemanea torulosa Kiitz. (nat. size). D, portion slightly magnified showing antheridial areas. E, Sacheria fucina (Bory) Sirodot, longitudinal section of fructiferous filament showing female organ ; t, trichogyne. F, Lemanea catenata Kiitz., transverse section of fructiferous filaments showing antheridia ; a, antheridial cell ; s, spermatium. (D, E, and F after Sirodot.) less regular intervals along their whole length are distinct swell- ings or nodes, and each nodulose thread is built up of an axial 42 Rhodophycece row of tubular cells surrounded by rows of smaller cortical cells, growth taking place in all cases by an apical cell. The only known method of reproduction is a sexual one. The antheridia are short, cylindrical cells developed on the exterior of the thallus, either on verticillate eminences or on the widest parts of the nodes. The procarp is unicellular and the carpogonium possesses a rather long, transparent, simple or branched trichogyne. After the fertilization of the carpogonium an ooblastema-filament is developed from it, at the extremity of which a bunch of jointed, moniliform filaments arise. Each of the swollen cells of these rnoniliform filaments becomes, when mature, a carpospore. The carpospores are thus produced inside the thallus, filling up the space between the central axis and the cortical cells of the fructiferous filaments. On development the carpospores produce the vegetative thallus, a protonema-like growth which has frequently been mistaken for a form of Chantransia. Genus Lemanea Bory, 1808. The vegetative thallus generally persists for several months, and is very branched but never pili- ferous. The fructiferous filaments are torulose, being regularly inflated at even distances, and are normally simple. The central axis of tubular cells is surrounded by a series of spirally twisted axial filaments, and the antheridial areas are in more or less com- plete rings round the nodes. L. torulosa Kiitz. ; em. Sirodot (fig. 3 C, D), and L. parvula Sirodot, are found in the rapid streams and torrents of certain parts of the British Isles. Genus Sacheria Sirodot, 187-2. The vegetative thallus is very fugacious. It is little branched, often piliferous, and exists for about a month (generally December or January). The fructiferous filaments are cylindrical or setaceous and usually branched. The central axis of tubular cells is quite devoid of axial filaments and the antheridial areas are on mamilliform projections, arranged in a verticillate manner at regular intervals. Species of this genus are much more frequent than species of Lemanea. Three species of the genus are widely distributed in the British Isles, — S. jluviatilis (Ag.) Sirod. (syn. Lemanea fluviatilis Ag.), S. fucina (Bory) Sirod., and S. mamillosa Sirod. (fig. 3 A, B), the last-mentioned one being the most abundant. It appears that S. mamillosa may sometimes occur in still water, as I have recently examined specimens of this species collected by Mr J. Murray from the west side of Loch Ness, Inverness. It must be remembered, however, that Loch Ness is a large body of water forming part of the Caledonian Canal, and probably numerous currents exist in it. Squamariaeece 43 Order II. CRYPTO NEMIACE^E. The fertilized carpogonium sends out a long, branched ooblas- tema-filament, the terminal cells of each branch conjugating with an auxiliary cell. From the latter the gonimoblasts arise. Family 1. SQUAMARIACECE. This family consists of a small group of marine, or rarely fresh- water Algae, which are minute, flat, gelatinous or membranous expansions, commonly encrusting stones, shells, or larger Algae. The thallus usually consists of dense, vertically arranged cell- filaments. Tetrasporangia are formed in various ways, and often give the surface of the thallus quite a verruculate appearance. The sexual organs are developed in cavities or ' conceptacles ' in the upper surface of the thallus. After the fertilization of the carpo- gonia these ' conceptacles ' contain numerous cystocarps. Genus Hildenbrandtia Nardo, 1845. This genus consists of a crustaceous expanded thallus, of a blood-red, dark red, rose, or brown colour, firmly adhering to rocks and stones on the sea-shore or in rivers and streams. The thallus is composed of compact, vertically arranged cell-filaments, with subcubical or oblong cells. The cell- walls are colourless and strong. There is only one British freshwater species — H. rivularis (Liebm.) J. Ag. (fig. 4) — which occurs as dark red patches on rocks and stones in streams and dripping places. Fig. 4. Hildenbrandt- ia rivtilaris (Liebm.) J. Ag., from Shipley Glen, W. Yorks. A, section of thallus. B, surface view (x400). C, two cells showing the chro- matophores ( x 800). Class 2. PH^EOPHYCE^: (or Fucoidese). ALMOST all the Algae of this class are marine and are known as the Brown Seaweeds. They are often termed the Melanophyceae. The thallus exhibits great diversity of form ; in some it is a simple filament, in others a flat expansion of cells, and in others it is greatly differentiated. The most highly organized of all seaweeds are members of this class of the brown Algse. The vegetative cells possess one nucleus, and the chromatophores have a distinct brown tinge owing to the presence of phycophcein and pkycoxanthin (the compound pigment being known as phseophyll). The former can be extracted with water and the latter by means of alcohol. Asexual reproduction is by motile cells or zoogonidia. Sexual reproduction is either by isogamous or heterogamous gametes, the conjugation of the gametes or the fertilization of the oospheres taking place in all cases outside the plant. The zygospore or the oospore always germinates directly. The motile reproductive cells, whether zoogonidia or gametes, invariably possess two cilia, inserted laterally, and in their movements one cilium is carried in a forward direction and one in a backward direction. The class is divided into a number of orders of which only one — — the Syngeneticce — is freshwater. Order I. SYNGENETICCE. The plants included in this order, which is sometimes termed the ' Phaeozoosporinae,' are exclusively freshwater. They are Algae of little note or importance, and may be either solitary or colonial unicells, multicellular, free-swimming or motionless. The cells are often naked, but at other times are surrounded by a mucilaginous cell-wall. In some of the multicellular forms the cells are only loosely held in position by a copious mucilaginous envelope. There is one cell-nucleus and one or more pulsating vacuoles. The Hydruracece 45 chromatophores, which are of a yellow or pale brown colour, may be solitary and excentric, or sometimes two in a cell, and pyrenoids are occasionally present. Vegetative multiplication occurs by simple cell-fission and asexual reproduction takes place by means of zoogonidia. The following seven families are the most important : — Fam. Hydruracece. Hydrurus Ag. Fam. Cryptomonadinacece. Cryptomonas Ehrenb. Fam. Chrysomonadinacece. Syncrypta Ehrenb. Synura Ehrenb. Uroglena Ehrenb. Fam. Dinobryacece. Dinobryon Ehrenb. Fam. Phceocapsacece. Phceocystis Lagerh. Phceococcus Borzi. Phceosphcera West & G. S. West. Stichogloea Chodat. Phceschizochlamys Lemm. Phceodactylon Bohlin. Fam. Choristocarpacece. Pleurocladia A. Br. Fam. Phceothamniacete. Phceoihamnion Lagerh. Only four of the above families are known to be represented in Britain, but probably all the others will be found in more or less abundance if searched for. Many of the plants of this order are plankton-forms, and the families Cryptomonadinacese, Chryso- monadinacese arid Dinobryaceas are truly flagellate in character. Family 1. HYDRURACE^l. The plants are attached, branched, and consist of a colony of unicells. The cells are at first spherical but afterwards become almost spindle-shaped, and are embedded in large masses of mucilage. They have one chromatophore and are destitute of a cell-wall. Asexual reproduction takes place by zoogonidia which are tetrahedric in form and possess one cilium1. They are only produced in the branches, two or four from each cell, and they germinate directly. After having come to rest, the zoogonidia attach themselves by the clear apex (at which point the cilium was inserted) and secrete a stalk-like mass of mucilage. This cell is the beginning of a new colony which is developed subsequently by its repeated divisions. Certain of the peripheral cells take on apical growth and produce branches. Resting spores (akinetes) have also been observed by Lagerheim. 1 Cfr Lagerheim in Ber. Deutsch. Bot. Gesell. 1888, p. 80, fig. xylogr. 1—3. 46 Phwophycece Fig. o. Hydrurus fostidus (Vill.) Kirchn. A, nat. size. B, zoogoni- dium (after Lagerheim). Genus Hydrurus Ag., 1824. The plants are branched colonies of unicellular units embedded in a tough, cylindrical mucilage. They vary from about 5 to 30 cms. in length and are of an olive green colour. The whole colony is simple below but branched above, often cut up into fine penicillate divisions, and covered with small villous projections giving it a plumose appearance. The entire structure behaves almost as a multicellular plant, growth in length being entirely dependent on single apical cells, and the branching is usually monopodial. The cells are commonly ellipsoidal and are more densely crowded in the small branches than in the main stems and branches. After- wards the cells elongate and become ar- ranged more or less in longitudinal groups. H. foetidm (Vill.) Kirchn. is found attached to stones and rocks in mountain streams. It is a sticky plant and gives off an offensive odour when alive. It is common in Central Europe and in the Arctic regions when the snows melt in the spring, but in the British Islands it is of very rare occur- rence, being known only from Yorkshire and Scotland. Family 2. CHRYSOMONADINACEJE. These are unicellular or colonial organisms which in the free condition are motile. Each individual consists of an oval or elongated cell, with either one or two cilia and either one or two brownish-green chromatophores. A red pigment spot is generally visible. The cells increase by longitudinal division. Genus Synura Ehrenb., 1838. This is a small, globose, free-swimming colony, formed of a variable number (from 10 to 50) of ovoid or ellipsoid, biciliated indi- viduals. They are arranged close together in a radial manner, and each individual possesses two chromato- phores and at the hinder end two pulsating vacuoles. Synura Uvella Ehrenb. (fig. 6) is commonly found in small ditches and pools, particularly if they are of rain-water. Pure collections of it can be frequently obtained in the early summer. Fig. 6. Synura Uvella Ehrenb. Single colony (x400), from Eldwick, W. Yorks. Dinobryacew 47 Genus Syncrypta Ehrenb., 1838. This is a motile colony similar in appearance to Synura but invested with a mucilaginous coat through which the cilia protrude. Syncrypta Volvox Ehrenb. is an abundant organism which bears great resemblance to Synura Uvella. Genus Uroglena Ehrenb., 1838. In this colonial form the cells are of the same nature as those of Synura, but the central portion of the colony is a hollow space filled with mucilage, and the ciliated cells are arranged round the periphery. Uroglena Volvox Ehrenb. is found in similar situations to those mentioned for the two previous genera. It is, however, much less abundant. Family 3. DINOBRYACE^. The individuals are attached to the bottom of a cup-shaped receptacle, which is widely open above. They are con- tractile and possess two cilia of unequal length. Genus Dinobryon Ehr., .1833. The cells are very delicate, of a somewhat changeable form, and are sensitive to stimuli. The lower end is attenuated into a stalk which is attached near the base of the open receptacle. There is one long cilium and one shorter secondary cilium. The chro- matophores are two in num- ber and of a yellow -brown colour. There is a pigment spot, two contractile vacuoles, and one cell-nucleus. The receptacle is campanulate or cylindrical, attenuated at its lower end into a straight or oblique point ; it is hyaline or sometimes coloured yellow or brown Fig. 7. A, Dinobryon cylindricum Imhof var. dlvergens Lemm.; two living examples from Eldwick, W. Yorks. ( x 730). B, en- cysted condition of same. C, Dinobryon Sertularia Ehrenb., colony with individuals encysted, from Cornwall ( x 410) ; c, cysts. 48 with oxide of iron, and the margins may be smooth or undulate. The multiplication is by longitudinal division or by the formation of globose resting-cells (or cysts) which are furnished with a peculiar projecting process (fig. 7 B and C). The cells occur singly or joined into dense, spreading colonies. The daughter-cells effect a lodgement above the inner rim of the mother-receptacle and then secrete a similar receptacle for themselves. Senn1 has written a good account of this genus, and Lemmermann2 has published a monograph of it, discriminating between fourteen species. Three species, D. Sertularia Ehrenb. (fig. 7 C), D. sociale Ehrenb. and D. cylindricwm Imhof, and varieties of them, are abundant throughout the British Isles, the first-named one being the most widely distributed. Species of this genus are very abundant in the freshwater plankton, the colonies of each species exhibiting a characteristic type of branching. D. protuberans Lemrn. and D.' elongatum Imhof are generally distributed but not abundant. Family 4. PHJEOCAPSACE^E. The plants are unicellular, forming colonies, the cells of which are embedded in a mass of mucilage. The cells are spherical or ellipsoidal and division takes place in all directions. The repro- duction is by zoogonidia and zoogametes. Genus Phseococcus Borzi, 18923. The cells are ellipsoidal or oblong-ellipsoidal, 6 — 11 /u, in diameter, and occur in twos, fours, eights or mul- tiples of these numbers, in hyaline gelatinous integuments which some- times show a delicate concentric struc- ture. There are two yellow-brown chromatophores in each cell and usually a red pigment-spot. The zoogonidia are ovoid or subpyriform. Fig. 8. PhcKOcoccus palu- dosus West & G. S. West, from Eldwick, W. Yorks. ( x 410). z, zoogonidia. P. dementi (Menegh.) Borzi has not been observed from Britain, but P. paludosm West & G. S. West occurs in moorland ditches. 1 Senn, 'Flagellata' in Engler and Prantl Natvirl. Pflanzenfam. I Theil. la Abth. '- Lemmermami, in Berichte Deutsch. Botan. Gesellsch. 1900, Bd xviii, pp. 500 — 524, t. xvii u. xix. a Borzi in Atti del Congr. Botan. Internaz. Geneva, 1892, pp. 463 — 471, t. xviii. Phmocapsacece 49 Genus Phaeosphsera West & G. S. West, 1902. The cells are large, exactly spherical, 14 — 17'5/i in diameter, and are embedded in small aggregates in a cylindrical, gelatinous integument which is sparsely branched. One brown.parietal chromatophore with somewhat irregular margins is present in each cell. P. gelatinosa West & G. S. West (fig. 9) is known from Sphagnum-\>og& in Cornwall. Genus Stichogloea Chodat, 1897 \ The cells are small, oblong or subovoid in shape, and are associated to form a membranous, gelatinous thallus of small size. The thallus is generally variously lobed and the cells are often somewhat radiately disposed. The cell-walls are firm and each cell contains a parietal chromatophore destitute of a pyrenoid. S. olivacea Chodat is known from the plankton of certain of the Scottish lakes. Length of cells 9— 15 /*. Fig. 9. Plueosphcera gelati- nosa West & G. S. West. A, portion of colony ( x 50). B and C, cells showing the solitary chromatophores ( x 410). From Tremethick Moor, Cornwall. 1 Chodat in Bull. L'Herb. Boiss. torn, v, no. 4, 1897, p. 302, t. 10, f. 8—12. W. A. Class 3. CHLOROPHYCE^E. THIS group, which includes all the green Algae, attains its greatest development in fresh water, and the number of species exceeds the combined total of the freshwater species of all other Algae. The simpler forms of green Algae are unicellular (e.g. some of the Protococcoideae and Desmidiaceae), some are ccenocytic (e.g. Vaucheriaceae, Sphaeropleaceae, Pediastrese), some are incompletely septate (e.g. Cladophoraceae), and others are multicellular or com- pletely septate (e.g. (Edogoniales, Chaetophorales, Zygnernacese). In other than the unicellular forms the thallus exhibits every degree of development from simple rounded cells to long, simple or branched filaments, flat expansions, or pulvinate masses of tissue. As a rule there is no differentiation of the ordinary vegeta- tive cells, but in some there is a marked distinction between the vegetative and reproductive cells. The cell-protoplasm (or cytoplasm) of the green Algae consists of a lining layer or ' primordial utricle ' which adheres closely to the cell- wall1, and, in many Algae, of additional anastomosing strands and threads traversing the interior of the .cell. It contains numerous granules of variable size which behave differently with staining reagents. Evidence goes to prove that there is no definite proto- plasmic continuity between the cells of multicellular green Algae. A division of labour is rarely observed amongst this class of plants, and in the Conjugatae the cells of most of the filamentous forms arc under normal circumstances quite able to lead an independent existence. The vacuoles are much as in other plant-cells and they contain a fluid usually known as the cell-sap. In the Conjugatae the cell-sap is occasionally coloured violet or purple owing to the 1 Cf. Chodat et Boubier, ' Sur la Plasmolyse et la membrane plasmique,' Journ. Bot. de Morot, Paris, 1898. Chlorophycece 51 presence of a pigment termed by Lagerheim phycoporphyrin1, This violet colour occurs normally in Ancylonema Nordenskioldii Berggr., Mesotcenium violascens De Bary, M. purpureum W. & G. S. West and Mougeotia capucina (Bory) Ag., and under excep- tional circumstances it is found in various species of Zygnema, Spirogyra and Desmids. The VolvocaceaB and the zoogonidia and gametes of other green Algae possess vibratile cilia, which are very variable in their length, number, disposition, and symmetry ; and in certain of the same forms contractile vacuoles are present. In the genera Tetraspora and Apiocystis ' pseudocilia ' are found, which do not possess any power of movement. A single nucleus is present in the cells of all the green Alga? except the ccenocytic and incompletely septate forms, and during the formation of asexual non-motile spores, zoogonidia, or gametes, it undergoes divisions corresponding to the divisions of the proto- plasm. In some green Algae mitotic division of a more or less complex character has been observed2. The cell-wall is very variable and its structure is often difficult of observation. In the formation of a cell-wall such as after the quiescence of a zoogonidium, it is developed on the outer surface of the protoplasm as the result of more or less complex processes. The young cell-wall usually consists of cellulose, but sometimes equally of pectose. Under the action of strong acids or other hydrating reagents an ordinary thick cell-wall will swell up and show traces of lamination. Each lamina represents successive layers of growth in thickness and in most plants consists of a mixture of cellulose and pectose constituents in variable propor- tions. In the Chlorophyceae these two constituents of the cell- wall are differentiated while the wall is very young. They exhibit considerable differences in their behaviour with reagents, the cellulose constituents giving a violet colour with chlor-zinc-iodine (Schulze's solution), whereas the pectose constituents do not. In many Algae the pectose constituents of the cell-wall are in the form of gelatinous layers on the outside of inner layers of cellulose. This mucilaginous material stains readily with aniline dyes such 1 Lagerheim in Vidensk.-Selsk. Skrift., I mathem.-natur. Kl., Kristiania, 1895, no. 5. 2 Observed in Spirogyra by Mitzkewitsch (Flora, Ixxxv, 1898) and C. van Wisselingh (Bot. Zeitung, Ivi, 1898 ; Flora, Ixxxvii, 1900) ; in Chlamydomonas by Dangeard (Le Botaniste, vi, 1899) ; in Closterium by Klebahn ; also in Botry- dium, etc., etc. 4 2 52 Chlorophycece as fuchsin, safranin, methylene-blue and gentian-violet. The outer layers often become thick coats of mucilage by the formation of series of pectose constituents which exhibit all stages between insolubility and complete solubility in water. It is not merely a hydration but a molecular change, and successive increments are often added by the gelatinization of other layers of the cell-wall. In some of the unicells the increase in thickness of the cell-wall due to gelatinization is only on one side and elongated colonies such as those of Hormotila are formed. The gelatinous pectose compounds although sometimes forming a large proportion of the cell -wall, do not alternate with layers of cellulose, but there appears to be a continual exudation of them through the inner layers of cellulose, a mass of jelly being thus formed on the outside of the cellulose wall. This is best seen in some of the Protococcoideae and Conjugates. The mucilage in which filaments of Algae are so frequently embedded exhibits a distinct radiating fibrillar structure which is clearly brought out by various reagents. The radiating structure of the enveloping mucus has long been known in the Conjugate and has at times given rise, especially in the Desmidiacese, to grave morphological misconceptions. The cell- walls of (Edogonium and other Algae exhibit peculiari- ties of structure which will be described in their respective families. Whatever the nature of the cell- wall one of its primary func- tions is the regulation of osmotic changes. Hairs and bristles are developed by certain green Algae belong- ing to the Coleochaetaceae, Herposteiraceae, CEdogoniaceae, Chseto- phoraceae and Chaetopeltidae. They are of many kinds, from slender articulate branches such as the piliferous apices of Chceto- phora, to exceedingly fine inarticulate hairs such as the setae of Bulbochcete, Herposteiron, Ckcetosphceridium, or Conochcete. The thallus often develops special root-like organs of attach- ment or haptera (commonly termed rhizoids), but these are as a rule only found in the young plants, most of the older ones occur- ring as freely floating masses. The chromatophores are usually distinct and in the forms with a filamentous or expanded thallus they are frequently characteristic of the different families or genera. They are of a bright green colour due to the presence of chlorophyll and are therefore chloro- plasts. Sometimes they are very difficult to define, but at other Chlorophycece 53 times they stand out clearly, occupying only a relatively small portion of the cytoplasm. They may be solitary or very numerous, of infinite variety of form, central or parietal, and the edges may be entire or deeply incised. In some forms they are ribbon-like and wound spirally round the interior of the cell-wall (e.g. Spirogyra, Genicularia, and some species of Spirotcenia), and in others they are central, spirally twisted masses (e.g. some species of Spirotcenia). Sometimes they are reduced and very pale in colour, and in the rhizoids and terminal cells of the hairs of some green Algae they are entirely wanting. The chloroplasts of most green Algae contain pyrenoids or proteid bodies which serve as a reserve of food-material. Much has been done towards the investigation of these bodies during the past few years and the presence or absence of pyrenoids has been regarded by some as a sufficient generic distinction. This is, however, attaching an importance to these proteid bodies which is scarcely borne out by facts. Although they frequently divide equally on the division of the cell, they also multiply without any cell-increase. They are likewise known to disappear during the development of certain species, and it has been clearly demon- strated that during certain stages of Tetraspora, Sphcerella and Eudorina they can arise spontaneously. Moreover, forms of An- kistrodesmus falcatus (Corda) Ralfs containing pyrenoids are sometimes met with in the same collection as others which have no pyrenoids. Similarly, the chromatophores of Debarya calospora (Palla) W. & G. S. West may or may not contain pyrenoids1. Starvation causes a disappearance of pyrenoids and they frequently increase in numbers if the cell is well nourished. On the whole, there is little . doubt that the presence or absence of pyrenoids depends largely upon external conditions and is a character to which a great deal too much importance has been attached in discriminating between the genera of green Algae. In the Chlorophyceae the stored product of assimilation is almost invariably starch. Exceptions to this are found commonly in Mesotcenium in the Desmidiacese and in the Vaucheriaceae. Cell-division generally takes place in all the cells of the thallus, but in a few instances there is a definite growing point which is usually an apical cell. 1 West & G. S. West in Ann. Bot. xx, March, 1898, p. 49; in Journ. Bot. Aug. 1900, p. 289. 54 Chlorophycece Multiplication by cell-division occurs in many of the lower forms of the Protococcoideae and in the Desmidiaceae. In the Zygnemaceae, and particularly in the smaller species of Spirogyra, the filaments often dissociate into solitary cells each of which then divides and forms a new filament. Asexual reproduction by zoogonidia is general throughout the class, although there is a notable exception in the Conjugate, in which motile reproductive cells are entirely wanting. In many of the Chaetophorales, Microsporales and Protococcoideae reproduction takes place by non-motile spores which may be either akinetes or aplanospores. Asexual spores are also more rarely found in the Conjugate, having been observed in Zygnema, Spirogyra, and in a few Desmids, and they are formed normally in the rare genus Gonatonema. Sexual reproduction occurs in most of the families of green Algae, and may be either isogamous or heterogamous. In iso- gamous reproduction the sexual organs are gametangia, usually giving rise to planogametes which conjugate and produce a zygo- spore. In the Conjugatae only aplanogametes are found. Many planogametes are generally produced from one gametangium, but only one aplanogamete. In heterogamous reproduction the sexual organs are oogonia and antheridia, and the gametes consist of oospheres and antherozoids. In all cases with the exception of Herposteiron, the oosphere remains in situ in the parent plant, being fertilized within the oogonium, and the result of fertilization is an oospore. The oogonia are always unicellular, and, except in Cylindrocapsa and some species of (Edogonium, so are the anthe- ridia. Only one oosphere is produced in an oogonium, except in Sphceroplea, and one, two, or many antherozoids may arise from an antheridium. The gametophyte is the principal generation, the sporophyte being generally represented by the sexually-produced spore. In Coleochcete, in (Edogonium, and in Mougeotia very rudimentary sporophyte generations consisting of several cells do exist. Of all freshwater Algae the Chlorophyceae have the most varied habitats. They are found in every possible damp or wet situation and some are epiphytes, others endophytes, and a few are even parasites1. 1 Phyllosiphon Arisari Kiihn (in Sitzungsber. d. naturf. Ges. in Halle, 1878) is a parasitic Alga observed only on the leaves of Arisarum vulgar e in Italy and the Chlorophycew 55 Richter1 and Comere2 have conducted experiments with a view to ascertaining if certain of the freshwater Alga?, especially Chloro- phycea?, can exist in salt water. Richter states that the lower the organization of the Alga the better its power of adaptation, but Comere finds that only those Algae with a robust structure and with large chloroplasts can successfully withstand immersion in salt water. Some species of (Edogonium and Cladophora can live in water containing 3'5 °/0 of sodium chloride, Vaucheria sessilis in water containing 2 °/0, and some of the large species of Spirogyra in water containing from T8 — 2°/0- Richter affirms that (Edogonium, Spirogyra, or Vaucheria have less power of adaptation to life in salt water than Stichococcus or Tetraspora. In all cases the salinity of the water caused the cells to increase in size and when the concentration was high malformation of the cells invariably occurred. Starch at first disappeared from the cells, but reappeared when the adaptation was more complete. Not- withstanding the somewhat contradictory nature of these two sets of experiments, it appears that certain of the freshwater Chloro- phycea? can adapt themselves to an increasing salinity of the water in a manner comparable with the adaptation of a few forms of the green Alga? to a life in hot water3. The class Chlorophycese can be conveniently subdivided into nine orders, all of which are found abundantly in the British Islands. Order I. (Edogoniales. Thallus filamentous, simple or branched. Cells uninucleate, with a large, parietal? anastomosing chloroplast containing one or several pyrenoids. Cell-division characterized by the inter- calation of a new piece of cell-wall between the mother-cell and the distal end of the daughter-cell. Sexual reproduction by heterogamous gametes. Zoogonidia with an anterior circle of cilia. Ex- clusively freshwater. south of France; P. maximus Lagerh., P. Philodendri Lagerh. and P. Alocasite Lagerh. are parasites on the leaves of species of Arisarum, Philodendrum and Alocasia in Ecuador (vide Lagerheim in Nuova Notarisia, 1892, pp. 120 — 124). Trichophilus Weber is a genus of Algae parasitic on the hairs of Bradypus (the Three-toed Sloth) ; another species has also been found on species of Nenia (Clausilia) ; cf. Lagerheim in Bericht. der Deutsch. Bot. Gesellsch. 1892, Bd x, Heft 8, pp. 514—517. 1 Kichter in Flora, Ixxv, 1892. 2 J. Comere in Nuova Notarisia, xiv, 1903, pp. 18 — 21. 3 G. S. West in Journ. Bot. July, 1902, pp. 242—243. 56 Chlorophycece Order II. Chcetophorales. Thallus filamentous, sometimes simple, but more often branched. Cells uninucleate ; chloroplasts parietal, generally single and with pyre- noids. Sexual reproduction either isogamous or heterogamous. Mostly freshwater. Order III. Ulvales. Thallus expanded, membranous, paren- chymatous, attached when young. Cells uninu- cleate ; chloroplasts single, parietal, with one pyre- noid. Sexual reproduction isogamous. Mostly marine. Order IV. Schizogoniales. Thallus filamentous, sometimes parenchymatous, or expanded by fusion of filaments in one plane. Chloroplast single, central and substellate, with one pyrenoid. Mostly subaerial. Order V. Microsporales. Thallus filamentous, unbranched. Cells uninucleate. with a large, parietal, reticulated or band-like chloroplast, destitute of pyrenoids. Exclusively freshwater. Order VI. Cladophorales. Thallus filamentous, simple or branched, incompletely septate. Segments large with numerous parietal chloroplasts each with a pyrenoid. Sexual reproduction isogamous or hetero- gamous. Marine or freshwater. Order VII. Siphonece. Thallus filamentous and coenocytic, unseptate, consisting of one large branched cell with many nuclei. Chloroplasts numerous, without pyrenoids. Sexual reproduction heterogamous. Mostly marine. Order VIII. Conjugates. Thallus unicellular or filamentous. Cells uninucleate ; chloroplasts single or several, usually large and of some definite shape, with pyrenoids. Sexual reproduction by isogamous aplanogametes. Exclusively freshwater. Order IX. Protococcoidece. Small unicellular, multicellular or colonial Alga3. Cells uninucleate or coenocytic ; chloroplasts very variable in form, size and disposi- tion, with or without pyrenoids. Sexual reproduc- tion of an isogamous or heterogamous character is known in some. Almost exclusively freshwater. (Edogoniacece 57 Order I. (EDOGONIALES. In this order the thallus consists of fixed, simple or branched filaments. The cells possess a single nucleus and the chloroplast is a parietal, more or less cylindrical, anastomosing mass of chloro- phyll, containing one or more pyrenoids. The vegetative division, in which a curious interpolation of new pieces of cell-wall takes place, is peculiar to the order. The zoogonidia are also anomalous, being characterized by a circlet of numerous cilia round the anterior end. In the autumn, plants of this order frequently have their cells packed with starch. The sexual organs are well-dif- ferentiated oogonia and antheridia, and the sexual reproduction is greatly specialized. There is only one family which includes three genera, two of which are abundantly found in the British Islands. Family 1. CEDOGONIACEJE. This family is represented in the British Isles by numerous species of the two widely distributed genera (Edogonium and Bulbochcete. The young stages of these plants possess well-de- veloped organs of attachment, but most of the species of (Edogo- nium float freely in the water when adult. The thallus is simple or branched and some of the cells exhibit a peculiar transverse striation at their upper extremities. This is particularly notice- able in the large species of (Edogonium and is the result of inter- calary surface growth. Beneath one of the transverse cell-walls an annular cushion of cellulose is deposited, and after each division a circular split is formed in the cell-wall opposite this cushion, the two parts remaining very slightly separated by a new piece of cell- wall derived from the cushion of cellulose. The rings or cushions of cellulose were investigated by Him1, who found that they consisted of a central mucilaginous mass, surrounded by a coating of cellulose formed as an inner cell-wall layer, which becomes intimately concrescent with the old membrane above and below the ring. After each division another slit is formed beneath and close to the first one, the process being repeated until the upper end of the cell frequently presents the appearance of having a number of ' caps ' placed one over the other (figs. 13 B and C ; 14 A), each ' cap ' indicating a division of the mother-cell. 1 Hirn in Acta Soc. Sclent. Fennicas, xxvii, 1900. 58 Chlorophycece Most of the cells in Bulbochcete are furnished with long tubular bristles and the terminal cell of the filament in one or two species of (Edogonium also ends in a long bristle (fig. 14 C). There _is_one large_j^1nroplast—in each cell disposed in the form. -of-a.^cYlindrical_nfit-work. a large proportion of it forming anastomosing cushions on the inner surface of the cell-wall. The pyrenoids vary from one to several according to the species, and sometimelT the number varies in different cells of the same plant. There is usually one nucleus with a prominent nucleolus (fig. 10 J ri), situated in a more or less central position. The nucleus occasionally divides without a corresponding division of the cell. Growth of the filaments takes place by the transverse division of any of the vegetative cells. Fig. 10. A — I, (Edogonium sp., from Frizinghall, W. Yorkshire, showing stages of one type of development from a zoogonidium in which the basal cell does not become greatly swollen ( x 460). p, pyrenoid. 3, (Edogonium sp., from Shipley Glen, W. Yorkshire, after treatment with Acetic Acid and Hffimatoxylin, show- ing nuclei (n), x 460. CEdogoniacece 59 Asexual reproduction takes place by means of zoogonidia, which are formed singly from ordinary vegetative cells. There is a re- juvenescence of the entire cell-contents, a large rounded mass being formed, which ultimately escapes. In (Edogonium this process may take place in any of the vegetative cells of the filament, whether terminal or not, and it sometimes occurs in a young plant consisting only of one cell. The cell-wall splits into two halves by a transverse slit near its upper extremity and the rounded mass of rej u venized protoplasm makes its exit in a delicate hyaline vesicle. This mass assumes a pyriform shape and at the narrower end a small colourless protuberance is formed, round the base of which arises a circle of numerous cilia (fig. 11 z). This striking zoogonidium, which may or may not possess a red pig- ment spot, quickly swims away, the entire process lasting only a few minutes. On coming to rest it attaches itself by its anterior hyaline end, loses its cilia, and develops a cell-wall. This cell ultimately forms a new filament by transverse cell- division (fig. 10 E— I). The basal cell may be rounded and swollen or it may develop a hapteron or organ of attachment (fig. 10 A — D). Wille has observed resting-spores in some species of (Edogonium1. The sexual reproduction in this family of Algae presents a greater specialization of the male and female organs than is found in any other family of the green Algae. The oogonia may be developed from any of the ordinary vegetative cells, and most frequently arise from cells which exhibit intercalary surface growth at their upper extremities. They are usually spherical or ovoidal in form and occur singly or in series of from 2 to 10. The contents of each oogonium become rounded off, forming a single oosphere 1 Vide Bot. Centralbl. xvi, 1883. Fig. 11. The escape of the zoo- gonidium (z) from its zoogonidan- gium. A, (Edogonium Boscii (Le Cl.) Wittr., from near Senens, Corn- wall. B, (E. Hirnii Gutw., from Churchill, Donegal, Ireland ( x 460). 60 Chlorophycece which contains much chlorophyll. The antheridia may be developed in the same filament as the oogonia, as in the monoecious species (fig. 12), or they may arise in separate male filaments, as in the dioe- cious species (figs. 13 and 14). The antheridia are sometimes unicellular, consisting of a short cell rather narrower than the ordinary vegetative cell and containing less chlo- rophyll. More frequently, however, they consist of more than one cell, and occasionally of a dozen or more, the contents of each antheridial cell dividing into two masses each of which becomes an anther- ozoid. Rarely only one antherozoid is produced in an antheridial cell. The antherozoids are similar in form to the zoogonidia and are ciliated in the same way, but they are smaller and contain less chlorophyll. Dioecious species in which the male filaments Fig. 12. Monoecious species of CEdogonium. A, a form of CE. obsoletum Wittr., from near Goring, Oxfordshire. B, CE. zig-zag Cleve var. are }arge an(J but little robustum West & G. S. West, from Harefield, Middlesex. C, CE. Itzigsohnii De Bary var. minor West, from the Orkney Is. D, CE. Ahlstrandii Wittr., from Pilmoor, N. Yorkshire (x460). oo, oogonium ; a, antheridium. inferior in size to the female filaments are said to be dioecious macran- drous (fig. 13). There is, however, another type of dioecious species in which the male plants are very small and are attached to the female plants ; these are said to be dioecious nannandrous (fig. 14). This type requires a further description. Certain short cells are produced in CEdogoniacece 61 the female filaments either singly or in chains, each cell being larger than the antheridial cells of the monoecious or dioecious macrandrous species, and known as an androsporangium. The androsporangium is usually produced in the neighbourhood of an oogonium and becomes the mother-cell of a motile ciliated spore known as an androspore, intermediate in size between an antherozoid and a zoogo- nidium. Each androspore swims about for a time and then attaches itself to the female plant, either actually on the oogonium or on some adjacent cell. It then sur- rounds itself with a cell-wall and grows into a very small male plant known as a 'dwarf- male ' or a nannandrium. The dwarf-male usually con- sists of a basal vegetative cell which supports one or more antheridial cells, but occasionally it is reduced to one antheridial cell only. Two antherozoids arise in each antheridial cell as in the ordinary monoecious and dioecious species, and they are set free by the splitting off of a cap if there be only one antheridial cell, or by Fig. 13. Dioecious macrandrous species of (Edogonium. A, male plant of (E. rufescens Wittr., from Scilly Is. B, female plant of same. C, female plant of (E. lautumniarum Wittr., from Welsh Harp, Middlesex. D, male plant of same (x460). oo, oogonium; a, an- ther id ium. the general dismemberment of the antheridium if there are several antheridial cells. When the oosphere is ready for fertilization a hyaline receptive spot appears in it at a point opposite that part of the wall of the oogonium which will open. The oogonium opens in many ways but the method of opening is constant for any one species. Some- times a circular crack is formed, which may be median, superior, or inferior ; sometimes a pore arises either in a superior or inferior 62 Chlorophycece Fig. 14. Dioecious nannandrous species of (Edogonium. A, a form of GE. undula- tum (Br£b.) A. Br., from Pilmoor, N. Yorkshire. B, (E. cyathigerum Wittr., from Bawcliffe Common, W. Yorkshire. C, (E. ciliatum (Hass.) Pringsh., from near Senens, Cornwall (x460). oo, oogonium; n, naunandrium or dwarf-male; a, antheridium. (Edogoniacece 63 position ; and at other times there is a distinct apical lid to the oogonium. An antherozoid finds its way through the opening into the oogonium, frequently having to accommodate itself to a passage much narrower than itself, and unites with the oosphere at the region of the receptive spot. After the fusion of the nuclei of the antherozoid and the oosphere the latter becomes the fertilized ovum or oospore, and it immediately surrounds itself with a cell- wall. The oospore then rests for a longer or shorter period, its chlorophyll disappears, its cell-wall increases in thickness, and its protoplasm becomes tinted with a red or brown pigment and filled with oil. On the decay of the walls of the oogonium the oospore is liberated and on germination its outer wall bursts and the contents, surrounded by a delicate membrane, are set free. With few exceptions a new plant is not immediately formed from the oospore, but the free cell-contents usually divide into four cells, each of which forms a rounded ciliated zoospore. The zoospores represent a rudimentary sporophyte generation, and after swarming for a while they come to rest and form new filaments. Sometimes the filaments formed from the zoospores are asexual and they give rise to several other asexual generations before forming a sexual plant. If the zoospores become fixed at once to some substratum, they form a hemispherical or spheroidal cell from a circular opening in which the new filament arises1. If they do not become fixed before germination haptera are usually developed (fig. 10 A — I). The principal investigators of this family of AlgaB have been Pringsheim and Wittrock, and quite recently it has been splendidly monographed by Him2. Genus CEdogonium Link, 1820. The plants of this genus are simple filaments with cylindrical cells usually slightly swollen at their upper extremities. The apical cell is generally terminated by an acutely conical cap or more rarely by an elongated bristle. The strong cell-walls and the swollen upper extremities of the cells, some of which possess the peculiar transverse striation, are characters which readily distinguish even sterile species of this genus from all other filamentous green Alga3. The adult plants usually occur floating in masses or they may remain attached to various water plants, and as the mucous covering on the exterior of the filaments is very slightly developed, they not only serve. as 1 Scherffel in Ber. Deutsch. Bot. Ges. xiK, 1901. 2 Hirn in Acta Soe. Scient. Fennicse, xxvii, 1900. 64 Chlorophycece hosts for various epiphytes, but they do not feel so slimy as most filamentous green Algse. There are about 80 British species of this genus, exhibiting great variation in size and in the relative proportions of the cells. They are exceedingly abundant, particularly in quiet waters, and with one or two exceptions the species can only be accurately identified from fructiferous specimens. They are frequently found in the fructiferous condition in suitable localities, such as small ponds and ditches, and more commonly in the south of England and south-west of Ireland than in other parts of the British Islands. The smallest British species is CE. tapeinosporum Wittr. (diam. of vegetative cells 2 '7 — 5/i), and the largest is CE. giganteum Kiitz. (diam. of vegetative cells 30 — 50 /x). (E. undulatum (Breb.) A. Br. (fig. 14 A) possesses very characteristic undulate Fig. 15. A, Bulbochcete subintermedia Elfv., from near Senens, Cornwall. B, B. Nordstedtii Wittr., from near Glendoan, Donegal, Ireland. C, B. nana Wittr., from Goring, Oxfordshire (x495). a, antheridium; and, androspo- rangium ; n, nannandrium; oo, oogonium. (Edogoniacece 65 vegetative cells, CE. punctato-striaturii De Bary has the entire filaments fur- nished with spirally arranged granules, and CE. acrosporum De Bary possesses a remarkable terminal oogonium. The oospores are either globose, ellipsoidal or ovoidal, and the cell-wall may be smooth, ridged, spiny, punctate, scrobicu- late or reticulate. Sometimes the oogonia are plicated as in CE. platygynum Wittr., or they may possess a transversely disposed ring of conical projections as in CE. Itzigsohnii De Bary (fig. 12 C). In some species the supporting cell of the oogonium is much swollen, as in CE. Borisianum (Le Cl.) Wittr. and CE. lautumniarum Wittr. (fig. 13 C and D). Rather less than half the known species are dioecious nannan- drous, and most of the remainder are monoecious. Genus Bulbochaete Ag., 1817. The plants of this genus are branched and every branch usually terminates in a long hollow bristle with a swollen base. The vegetative cells widen Upwards, most of them carrying a laterally placed bristle, and they do not reach the same relative length as those of (Edogonium. The oogonia are generally terminal on short lateral branches ; and, with few exceptions, the supporting cell of the oogonium is divided by a transverse septum, the position of which is fairly constant for any one species. In the dioecious nannandrous species the andro- sporangia are commonly situated on the apices of the oogonia. The plants occur as branched tufts, more often fixed than in the preceding genus, and they possess a quantity of enveloping mucus, affording a home for numerous Diatoms and often Desmids. There are about 14 British species, of which B. nana Wittr. (diam. of vegetative cells 10 — 15 p.; fig. 15 C) is the smallest and B. gigantea Pringsh. (diam. of vegetative cells 24 — 32 p.) the largest. No doubt many more species will be found if searched for, but in the greater part of the British Islands fructiferous specimens are relatively scarce. There is great variability in the form and size of the vegetative cells in the different species, arid also in the comparative size and length of the bristles. The genus is not so abundant as CEdogonium, and all the species prefer very still waters. Most of the species of this genus are dioecious nannandrous. Few species are monoecious, and dioecious macrandrous species are as yet unknown. w. A. 66 Chlorophycece Order II. CH^ETOPHORALES. In this order of green Algae the thallus is filamentous, sometimes simple, but more frequently branched. The brandies are generally attenuated and often piliferous. The cells possess one nucleus, and in all the families of the order, except the Trentepohliacese, there is a single parietal chloroplast with one or more pyrenoids. Asexual reproduction takes place often by resting-spores, which may be either aplanospores or akinetes, and commonly by zoogonidia with two or four cilia. Sexual reproduction is brought about by isogamous planogametes with two cilia, or by well-differentiated heterogamous gametes. This order has also received the name of the " Ulotrichales," but I prefer to accept Wille's name of the " Chastophorales " as five out of the seven families include branched Algae. Family 1. Coleochcetacece. Flat expansions or pulvinate branched masses, epiphytic on the stems and leaves of submerged plants. Sexual reproduction heterogamous ; plants monoecious or dioecious ; oogonia with a trichogyrie and one non-motile oosphere; fertilization within the oogonium and resulting in the formation of a cortical layer on the outer surface of the oogonium. Some of the cells of the thallus are furnished with fine bristles with basal sheaths. Family 2. Herposteiracece. Filaments branched, creeping, epi- phytic on submerged plants. Sexual reproduction heterogamous; plants monoecious ; oospheres motile, fertilization taking place outside the oogonium. Cells with one or several long bristles, sometimes swollen at the base. Family 3. Vlotrichacece. Filaments simple. Chloroplast single, parietal, with one or many pyrenoids. Sexual reproduction isogamous. Family 4. Cylindrocapsacece. Filaments simple ; cells with thick lamellose coats, usually arranged in a single series within a lamellose gelatinous sheath. Sexual reproduction heterogamous ; plants monoe- cious ; oogonia with one non-motile oosphere ; fertilization within the oogonium. Family 5. Chcetophoracece. Filaments branched ; branches attenu- ated into multicellular hair-like prolongations. Chloroplast single, parietal, with one or many pyrenoids. All the cells except those of the rhizoids and hairs are capable of producing zoogonidia or gametes. Sexual reproduction isogamous. Family 6. Microthamniacece. Filaments branched ; branches scarcely attenuated, not piliferous. Chloroplast single, parietal, with Coleochcetacece 67 or without a single pyrenoid. Zoogonidia and gametes produced in special gonidangia. Sexual reproduction isogamous. Family 7. Trentepohliacece. Thallus branched, terrestrial or ar- boreal. Chloroplasts several, parietal, without pyrenoids. Zoogonidia and gametes produced in special gonidangia. Sexual reproduction isogamous. Family 1. COLEOCILffiJTACEJE. The plants included in this small family have reached a higher stage of development than any other of the green Algae, and have undoubtedly arisen from the Chsetophoraceae by further speciali- zation. They form small discs or cushion-like masses, which are enveloped in mucilage and are attached to the stems and leaves of larger water-plants. In the commoner forms the thallus is more or less circular in outline and disc-like in form, consisting of a Fig. 16. Coleochate scutata Breb. ( x 100), from Welsh Harp, Middlesex. single layer of cells in one plane, which either form a compact parenchymatous layer, or are arranged in the form of branched filaments radiating from a central point. In other species the ramification is not confined to one plane, but numerous ascending branches are given off, the whole thallus sometimes having the appearance of a hemispherical cushion. The peripheral cells of the disc or the terminal cells of the branches are meristematic and the thallus grows by the formation of new radial and tangential cell-walls. The branching is in some species dichotomous, but in others it closely resembles that of Chcetophora or Myxonema. 5—2 68 Chlorophycece Some of the cells are furnished with a colourless bristle which is fixed at its base into a narrow sheath of considerable length. / Asexual reproduction takes place by means of large ovoidal zoogonidia (fig. 17 D), furnished with two long cilia and produced singly from the cells of the thallus, more particularly from the terminal cells of the branches. The zoogonidium escapes from the zoogonidangium either by a round orifice on the upper surface or by the dissolution of the extremity of the terminal cell. Sexual reproduction is brought about by the fertilization of an oosphere by an antherozoid. The sexual organs are oogonia and Fig. 17. Coleochcete pulvinata A. Br. A and B, from near Glenties, Donegal, Ireland ; A, portion of thallus with sexual organs ( x 460) ; o, oogonium ; t, trichogyne ; a, antheridia. B, ripe ' spermocarp ' emitting the cells formed by the division of the oospore ; each of these becomes a zoospore ( x 460). C, zoospore (after Chodat). D, zoogonidium (after Pringsheim). antheridia. The oogonium is developed by a swelling of the terminal cell of a branch and it possesses on its upper surface a narrow trichogyne. An oosphere containing chlorophyll is pro- duced within the oogonium, and just previous to fertilization the trichogyne opens at the apex and exudes a colourless drop of mucilage. The antheridia are flask-shaped cells which are developed from cells in the neighbourhood of the oogonium, or in direcious species from cells of another thallus. Only one antherozoid is Coleochcetacece 69 produced in an antheridium and it can only be distinguished from a zoogonidium by its smaller size. After fertilization the oospore surrounds itself with a cellulose wall and grows considerably in size. At the same time the oogonium becomes closely covered with a layer of cortical cells, produced by the proliferation of the supporting-cell and by the close application of the terminal cells of other branches. The fertilization and the formation of this cortical layer are said by Pringsheim to take place from May to July. The whole structure produced after fertilization, and which presents the appearance of a sphere supported on one or many filaments, has been termed a "spermocarp." The cortical cells often become dark brown or red in colour and lose their chlorophyllaceous con- tents. Usually this structure remains dormant through the winter, the maturation of the oospore taking place slowly. On germination the oospore divides into a number of cells and the cortical layer splits irregularly into two halves. The escaping spores (fig. 17 B), which become more or less irregular in outline, do not give rise directly to a new thallus, but each one becomes a zoospore with two cilia. The zoospore (fig. 17 C) gives rise- to several rudi- mentary asexual generations which are propagated by zoospores, and finally to a sexual individual. Genus Coleochaete Breb., 1844. The thallus is filamentous, branched, erect or creeping, usually forming a flat pseudo- parenchymatous plate with peripheral growth. The bristles, which are sparsely scattered over the upper surface of the thallus, are not always clearly visible, and they are characterized by the well- marked sheathing base. The plants are all epiphytes with a marked dorsi ventral development, but there are no special organs of attachment. Each vegetative cell possesses a large nucleus and a single parietal chloroplast of irregular form, which contains one or two large pyrenoids. The plants occur attached to the submerged portions of various aquatic and marsh plants from which they are not easily removed. C. scutata Breb. and C. solnta Pringsh. are the most abundant species in Britain. The former possesses a compact, flat, parenchymatous thallus (fig. 16) and the latter a flat thallus composed of dichotomously branched filaments radiating in one plane from one or more central cells. The diameter of the thallus in each case scarcely exceeds 700 — 800 /u. and the cells average about 10 — 2.3 p in diameter. C. orbicularis Pringsh. possesses a flat, expanded, circular thallus which reaches a diameter of 4 mm., in which the filaments are very closely packed and the cells are rather small. C. pulvinata A. Br. 70 Chlorophycece forms hemispherical cushions commonly 2 — 4 mm. in diameter, but occasion- ally greatly exceeding these dimensions. The filaments are erect and radiating and the cells are 1 — 3 times longer than their diameter, which is from 20 — 50 /* (fig. 17). This species is more frequently observed with sexual organs than any of the others. C. irregularis Pringsh. possesses a more or less parenchy- matous thallus in which the branching is very irregular. All the species are readily eaten by pond-snails of the genera Limncea and Planorbis. Family 2. HERPOSTEIRACEJE. This is a small family including only the genus Herposteiron. The plants are epiphytic on larger Algae and on other water-plants, and occur as short irregular filaments which are little branched. Most of the cells of the filament possess one or more bristle-like setae or hairs, cut off from the cell which bears them by a basal Fig. 18. Herposteiron con/ervicola Nag. (= Aphanochcete re.pens A. Br.). oo, oogonium ; os, oosphere ; a, antheridium ; an, spermatozoid. (After Huber.) septum. Chodat has found that in cultures the setae are sometimes replaced by branches, showing the relationship between this genus and the Chsetophoracese. Asexual reproduction takes place by zoogonidia, one to four being produced from the mother-cell, the wall of which ruptures and sets them free. They vary much in size, possess four cilia, and usually a red pigment-spot. On coming to rest thej^ generally develop unilaterally into a new plant. Sometimes aplanospores are formed (fig. 19 Co). The sexual reproduction of Herposteiron is of special interest. The oogonia are differentiated from certain of the central cells of Herposteiracece 71 the thallus which are devoid of bristles. These cells grow in size, assume a globular form, and become filled with starchy and oily material. One oosphere is produced, which is motile, having four cilia, and is expelled from the oogonium by the rupture of the upper portion of the wall. The antheridia are small cells usually developed at the ends of the filaments and branches ; they are frequently colourless and are considerably smaller than the ordinary vegetative cells. One or two antherozoids are produced in an Fig. 19. A, Herposteiron pilosissima (Schmidle) nob., from Wimpole Park, Cam- bridgeshire. B — D, H . confervicola Nag. ; B and C, from Bradford, W. Yorka. ; D, from Kichmond Park, Surrey (x450). a, aplanospore. antheridium. These are pear-shaped bodies with four cilia and two pulsating vacuoles, and are much smaller than the zoogonidia. They escape into a hyaline vesicle which soon becomes diffluent and sets them free. The antherozoids move about very rapidly, but the movements of the oosphere are very feeble. The Herpo- steiracese is the only family of the Chgetophorales in which the fertilization of the oosphere takes place outside the oogonium. Little is known concerning the development of the oospore. Genus Herposteiron Nag., 1849. [Aphanochcete A. Br., 1851 ; Berth., 1878 ; Huber, 1892.] The thallus is filamentous, creeping 72 Chlorophycece and branched, the terminal cells of the branches being rather smaller than the more central cells of the thallus. One or more erect bristles are attached to the dorsal surface of some or all of the cells. These bristles are single, attenuated, and very elongated cells, which have lost their protoplasmic contents and which never possess chloroplasts. They are somewhat fragile and are easily broken off near the base. The sexual organs, which are of very rare occurrence, have been described by Huber1, The plants occur as epiphytes on species of CEdogonium, Cladophora, Rhizodonium, and Mougeotia, and also on the leaves of Lemna, Elodea, etc. Sometimes well-developed specimens are much branched, the procumbent branches of the Alga often following the contours of the cells of the plant to which it is attached, and in consequence exhibiting a marked reticular structure2 (fig. 19 B). The cells contain a single parietal chloro- plast with one (or more ?) pyrenoids. There has been much confusion with regard to the two names Aphanochcete and Herposteiron. The arrangement proposed by .Hansgirg, and subsequently adopted by De Toni, Wille and others (myself included), of two distinct genera is quite untenable. There can be no doubt in the mind of anyone who has studied these plants carefully that Herposteiron confervicola Nag. and Aphano- chcete repens A. Br. are descriptions of the same plant, and this is amply confirmed by the authentic drawings by Nageli published by Huber. Both Huber and Klebahn admit the identity of Herposteiron and Aphanochcete, but reject Nageli's name on the ground of the incompleteness of the description. There is, however, far more reason for neglecting Braun's name on the ground of inaccuracy. H. confervicola Nag. ( = Aphanochcete repens A. Br.) is a species with oblong-ellipsoidal cells, each bearing a single bristle which is little swollen at the base and which is attached towards one end of the cell. It is not an un- common species and is somewhat variable, two bristles being frequently attached to some of the cells of the thallus. (Figs. 18 and 19 B — D.) Another species, H. pilosissima (Schmidle) nob. ( = Aphanochcete pilosissima Schinidle), is more abundant in some parts of the British Islands and is most probably identical with H. polychcete Hansg. The cells are more ellipsoidal and possess from one to four bristles, each bristle having a swollen base (fig. 19 A). 1 Huber in Bull, de la Soc. hot. de France, xli, 1892. 2 G. S. West in Journ. Bot. Febr. 1899, p. 57. Ulotrichacece 73 Family 3. ULOTRICHACEJE. This family includes a few genera which are readily distin- guished from other plants of • the Chsetophorales by their un- branched habit and by the structure of their cells. The thallus is a simple filament, consisting of cylindrical or doliform cells, as in Ulothrix, or of rounded cells arranged in a single series and enveloped in a thick mucous coat, as in Hormospora and Radio- jilum. The cell-wall is always hyaline and colourless, but varies much in thickness. It is sometimes delicate, sometimes thick and lamellose, and sometimes the outer layers are diffluent. There is a single, parietal, plate-like chloroplast in each cell, with an entire or variously lobed margin, and containing one or many pyrenoids. A single nucleus is present in the cytoplasm. Asexual reproduction takes place in several ways. Sometimes aplanospores are produced (fig. 20 Da; fig. 21 Fa), or numbers of akinetes1 are formed by the enlargement of certain cells and the gelatinization of the outer portions of their original cell-walls (fig. 21 E and I) ; these may be resting-spores (hypnospores) or they may germinate directly. Sometimes the thallus is multiplied by a general dismemberment of the filament into single cells or groups of cells, each cell or group developing into a new filament. Zoogonidia of two kinds are produced, often from different cells of the same filament; small microzoogonidia with two cilia and larger macrozoogonidia with four cilia. The microzoogonidia are produced from certain of the. vegetative cells which have become microzoogonidangia and in the larger species of Ulothrix, such as U. zondta, 16 or 32 are produced from each gonidangium, but in U. subtilis only 2 or 4 are produced. Similarly 2, 4, or 8 macro- zoogonidia are usually produced from a macrozoogonidangium, but in U. subtilis only one arises. It is occasionally observed that the entire contents of the cell are not used up in the formation of the macrozoogonidia (vide fig. 21 G). The zoogonidia germinate di- rectly on coming to rest, sometimes even within the mother-cell, and the plants which arise by the germination of the macro- zoogonidia are larger than those which arise from the micro- zoogonidia. This accounts for the variability in size of the filaments which is so often observed in a collection of any one 1 This was first shown by Wille in Bot. Centralbl. xi, 1882, p. 113. 74 species of Ulothrix. Occasionally the zoogonidia do not escape, but lose their cilia, become invested with a cell-wall, and . form what is termed a " palmelloid condition " (fig. 20 F). The produc- tion of zoogonidia usually commences near the apex of a filament and progresses towards the base. Sexual reproduction is by the conjugation of isogamous gametes, which are indistinguishable from the microzoogonidia. The gametes are biciliated and usually escape from the gametangia in the morning, conjugating in pairs with considerable rapidity. The Fig. 20. A and B, Ulothrix zonata (Web. et Mohr.) Krttz., from near Meaux Abbey, E. Yorkshire (x500). C — F, U. subtilis Kiitz., from near Mullion, Cornwall (x500); F shows the "palmelloid condition"; a, aplanospore ; za, macro- zoogonidium ; zi, micro/oogonidium. resulting zygospore invests itself with a firm cell-wall and germi- nates after a more or less extended period of repose. On germina- tion the contents break up into many zoospores each of which forms a new filament. The gametes frequently germinate directly without conjugation. The movements of the microzoogonidia and gametes are fre- quently very strange, one cilium being kept more or less rigid and its extreme apex used as a pivot, while the other cilium exhibits violent movements causing a rapid lateral oscillation of the body. Ulotrichacece 75 The British genera are best arranged as follows : — , . * Filaments thread-like, cells cylindrical with truncate apices, t Filaments long and flexuose, attenuated towards base Ulothrix. tt Filaments short, attenuated at both base and apex Uronema. t+t Filaments of variable length ; transverse walls very thick; cells in pairs Binuclearia. ** Filaments fragile, often moniliforin, cells with rounded apices. •f- Cells more or less cylindrical ; plants with a re- semblance to a fragmented Ulothrix; with no prominent mucous coat Stichococcus. tt Cells cylindrical with hemispherical ends, or sub- globose, often remote ; with a prominent mucous envelope. § Cells cylindrical. j Cells equidistant, often in close contact. © Cells large, short Hormospora. ©® Cells minute, more elongate Glceotila. H Cells in pairs Oeminella. §§ Cells rounded Radiofilum. The three genera Hormospora, Glceotila and Geminella are scarcely to be distinguished from each other. Perhaps it would be better to unite them under the name Geminella. Genus Ulothrix Kiitz., 1833. [Hormiscia in the sense used by Rabenhorst (1868), Hansgirg, and De Toni.] In this genus the filaments are simple, not attenuated at the apex, but fre- quently fixed at the base by a unicellular, simple or ramified ' rhizoid.' The cells are commonly cylindrical or sometimes swollen, and in the larger species the cell-wall is thick and evidently lamel- lose. '" The chloroplast is parietal with one or many pyrenoids, and varies much in its relative size. The genus Ulothrix was established by Ktitzing1 for the species U. zonata two years before Fries' description of Hormiscia*. Areschoug's3 enlargement of the genus Hormiscia was based upon erroneous conceptions, as he included in it species having no affinity with each other. The original Hormiscia of Fries only included two Algae previously known as "Conferva penicilliformis Roth" and "Conferva Wormskioldii Flor. Dan." These Algas are commonly placed under the genus Urospora of Areschoug, but the 1 Kiitzing in Flora, 1833, xvi, p. 517. 2 Fries in Flora Scand. 1835, p. 327. 3 Areschoug in Acta Beg. Soc. Sci. Upsala, ser. in, vol. vi, no. 2, p. 12. 76 Chlorophycece latter genus should undoubtedly be placed as a synonym of Hor- miscia Fries. The best known species of the genus is U. zonata (Web. et Mohr.) Kiitz., (tig. 20 A and B), which is widely distributed all over the British Islands, occurring as bright' green masses in streams, rivers, etc., more especially in the early spring. The cells vary from 15 — 70 p. in diameter and the cell-walls, are very thick and lamellose. An abundant British species is U. subtilis Kiitz. Fig. 21. A — F, Ulothrix cequalis Kiitz.; A — D, from Putney Heath, Surrey; E and F, from Mitcham Common, Surrey; A, filament showing escape of micro- zoogonidia; B — D, germinating macrozoogonidia, C shows the same plants aa B 48 hours afterwards, D is much further advanced ; E, portion of filament of akinetes ; F shows two aplanospores which have taken exactly 14 days to develop from ordinary vegetative cells. G, U. cEqualis Kiitz. var. catceniformis (Kiitz.) Rabenh., from near Bradford, W. Yorkshire, showing escape of macro- zoogonidia. H, U. moniliformis Kiitz., from Wimbledon Common, Surrey ; I, the same with akinetes. (All x 500. ) a, aplauospore ; ak, akinete ; za, macro- zoogonidium ; zi, microzoogonidium. (fig. 20 C— F), the cells of which are as long as broad and from 4 — 8 /* in diameter. A variety of this species — var. variabilis (Kiitz.) Kirchn. — is probably the most abundant member of the genus, being generally distributed in the stagnant waters of ponds, ditches, troughs, rain-tubs, etc. It is a little thicker than U. subtilis and the cells are 1^ — 2j times longer than their diameter. U. cequalis Kiitz. (fig. 21 A — F) and U. moniliformis Kiitz. (fig. 21 H — I) are other well-known species. Another Alga — Schizomeris Leibleinii Kiitz. — which I have only once seen, from Stone Ghyll, Dodd Fell, N. Yorkshire, should perhaps be included here. I am doubtful as to the exact determination of the Yorkshire specimens, but they reminded one very much of a large Ulothrix zonata, attenuated both at the apex and the base, the latter being fixed to rocks and stones in the spray of a waterfall. Longitudinal division of the cells had occurred at intervals, so Ulotrichacece 77 9 e that the filaments often consisted of a double row of cells. Wolle seems to have observed the same plant from several parts of the United States (cf. Freshw. Alg. of U. S. t. cxxv). Genus Hormospora Br£b., 1840. The filaments are simple and free-floating, rarely fixed by a mucous disc, and they consist of a single series of cells embedded in a thick, cylindrical, mucous in- vestment. This outer gelatinous coat varies in its relative size, and is always hyaline and homo- geneous. The cells are commonly oblong-cylindrical with broadly- rounded extremities, and they contain a single parietal chloro- plast usually disposed as an equatorial band. One pyrenoid is generally present in each chlo- roplast, although rarely pyrenoids are quite absent. The genus is very closely allied to Ulothrix, but is distinguished by its thick gelatinous coat and by the con- stant separation of the cells after Breb., from near Mullion, Cornwall, division. Cienkowski and others B> H- ordinata West & G- s- West. have regarded the genus as a mere state or condition of Ulothrix, but I think that is open to much doubt. The cell-wall is extremely thin and delicate, and the formation of zoogonidia has not been observed. The most frequent British species is H. mutabilis Breb. (fig. 22 A), which occurs principally in bogs, especially amongst Sphagnum, and in such localities species of Ulothrix do not usually exist. The cells are 16 — 19 //, in diameter and 1^ — If times longer than broad. H. ordinata West & G. S. West (fig. 22 B) is a smaller and much rarer species with cells 5 -8 p. in diameter. H. plena Breb. is the only other British species. Genus Glo3otila Kutz., 1843. This is a genus of small Algse intermediate in character between Hormospora and Ulothrix. The cells are very small, oblong or elliptical and more or less moniliform, but they are not so completely separated as those of Hormospora', they are arranged in a single series in a delicate mucous envelope, and each one contains a parietal chloroplast of small size which is disposed as in Hormospora. I have not Fig. 22. A, Hormospora mutabilis from Cam Fell, W. Yorkshire. C— E, Glceotila protogenita Kiitz., from Pil- moor, N. Yorkshire. ( x 440.) 78 Chlorophycece observed any pyrenoids in the chloroplasts of this genus. Borzi1 has recently described the formation of zoogonidia. The cells of G. protogenita Kiitz. (fig. 22 C — E), which is the typical species of the genus, only reach a diameter of 3 — 4'5 /x. The plants are very rare and occur in bogs or boggy pools. Genus Geminella Turp., 18283; Lagerh., 18833. [ ? Planctonema Schmidle, 1903.] This genus is scarcely to be distinguished from Hormospora Breb. except for the arrangement of the cells in pairs. The cells are fairly remote, are enveloped in a thick mucous coat, and after division the daughter-cells separate only very slightly. The chloroplast is exactly as in Hormospora. The cells of some of the filaments occasionally develop thick brown cell-walls and become resting akinetes. G. interrupta Turpin (fig. 23 A — C) is the only known species and it is rarely found in the British Isles. The cells are 6'5 — 7 /u. in diameter. It would perhaps be more correct to unite the genera Geminella and Hormospora, the former having priority. It is impossible to find any generic characters sufficient to separate Planctonema Schmidle from Geminella or Glosotila. Genus Radiofilum Schmidle, 1894. The filaments are simple, sometimes short and fragile , some- times long and flexuose, and they are enclosed in a considerable mucous sheath, which exhibits a more or less distinct radiating fibrillar structure. The cells are globose, ellipsoid, or sublenti- cular, free and distant or joined by a narrow hyaline bridge, always forming moniliform filaments after the manner of those of the Fig. 23. A — C, Geminella interrupta -»T T i. n ^i Turp. ; A and B, from near the Lizard, Nostocaceae. In each Cell there Cornwall ( x 440) ; C, two resting aki- is One chloroplast containing a netes from Glen Tummel, Perthshire, . , -IT • Scotland ( x 350). D, Radio fiiumflaves- single pyrenoid. In one species cens G. S. West, from Wicken Fen, the cell- wall is composed of two Cambridgeshire ( x 440). 1 Borzi, ' Studi Algologici II.' 2 Turpin in Me"m. du Mus. d'hist. nat. 1828, torn, xvi, p. 329, t. 13, f. 24. 3 Lagerh. in Ofvers. af K. Vet.-Akad. Forh. 1883, no. 2. Ulotrichacece 79 equal halves, but in others it is not. The cells multiply by division which is preceded by a division of the chloroplasts and pyrenoids. The type species of the genus, JR. conjunctivum Schmidle1, has not been observed from Britain. R. flavescens G. S. West (fig. 23 D) is a larger species, with much longer flexuose filaments and broad elliptical cells ; the diameter of the cells is 7 '5 — 10-5 p and the chromatophores are of a yellowish- green colour. Genus Stichococcus Nag., 1849. [Hormococcus Chodat, 1902.] The filaments are entirely or very largely aerial, and are composed of cylindrical cells. They readily become disarticulated into frag- ments composed of a few cells, the extremities of the terminal cells being broadly rounded. There is one parietal chloroplast in each cell, plate-like or more or less irregular in form, and occupying as a rule only a portion of the cell-wall. A small pyrenoid is present in each. In some of the aquatic forms of Stichococcus flaccidus I have observed a fragmenta- tion of the chloroplast (cf. fig. 24 B). The plants are propagated by division of the cells and fragmen- tation of the filaments, by akinetes, and by zoogonidia. The latter are bi- ciliated, have no pigment spot, and arise singly from cells which are under- going rapid division. This genus much resembles Ulothrix, but its adaptation to an aerial existence has caused a multiplication by dis- articulation of the filaments and a reduction almost to a unicellular con- dition. This disarticulation often takes place first on one side and then on the other, giving a zig-zag appearance to the disarticulated filaments. Klebs has shown that it is facilitated either by too much or too little nourishment. The genus was well studied by Gay2. There appears to be no justification whatever for Chodat's name "Hormo- Fig. 24. A, Stichococcus bacillaris Nag., from Saltaire, W. Yorkshire. B, S. flaccidus (Kiitz.) Gay, from Barnes Com- mon, Surrey. C, S. dissectus Gay, from damp walls, London. D, S. variabilis West & G. S. West, from Bradford, W. York- shire ( x 440). coccus. 1 Schmidle in Flora, 1894, Heft 1, p. 47, t. vii, f. 4, 5. 2 Gay, 'Becherches sur le devel. et les classif. de quelques Algues Vertes,' Paris, 1891. 80 --•. S. bacillaris Nag. (fig. 24 A) is an abundant species on damp earth, walls, palings, etc. ; diam. of cells 2'7 — 3-8 p. S.flaccidus (Kiitz.) Gay (fig. 24 B) is a larger species frequent on wet stones arid in rain-pools ; diam. of cells 7— 10-5 /i. S. dissectus Gay (fig. 24 C) is a closely allied species to S.flaccidv*, or perhaps only a form of it. S. variabilis West & G. S. West (fig. 24 D) forms a thin green stratum on wet stones in the neighbourhood of waterfalls ; the cells are very irregular in outward form and the chloroplast is often devoid of a pyrenoid or may even possess two ; diameter of cells 3 — 6 p.. Genus Uronema Lagerh., 18871. The filaments are simple, relatively short, and destitute of a mucous coat; they consist of cylindrical cells, the apical cell being acuminate and the basal cell attenuate. The plants are fixed by a disc secreted by the basal cell. The chloroplast occupies a con- siderable area of the cell- wall and is parietal, containing two pyrenoids. The cell-wall is firm and thin. The zoogonidia are produced singly or in pairs from each cell; they possess four cilia and a subapical pigment-spot. Sometimes the zoogonidia are arrested in their escape, the cilia are not de- veloped, and an aplanospore is produced by the acquirement of a strong cell- wall. The only species is U.confervicolum Lagerh. with filaments 4 — 6 p in diameter and cells 2 — 3 times longer than broad. It is an ex- ceedingly rare plant, disti nguish ed from species of Ulothrix by its short filaments, by the attenuation of the apical and basal cells, by the chloroplast, and by the firm cell-walls. I have only met with it in abundance from the Orkney and Shetland Is. I 'I U c Fig. 25. A — E, Binuclearia tatrana Wittr., from Lewis, Outer Hebrides ( x 440). The genus Rhaphidonema Lagerh. (of which R. nivale is known from W. Yorks.) is a fungus. Genus Binuclearia Wittr., 1886 2. The filaments are simple and attached when young by a hapteron from the basal cell. The cells are cylindrical with firm, distinctly lamellose cell-walls, the transverse walls being unequal, a thin one and a very thick one alternating. The cells thus appear to be arranged in pairs. The 1 Lagerh. in Malpighia 1887, p. 518, t. xii, f. 1—10. 2 Wittr. in Wittr. and Nordst. Alg. Exsic. 1886, no. 715. See also Schroder in Forschungsberichte aus der biol. Station zu Plon, Teil vi, 1898, p. 19—21. Cylindrocapsacece 81 chloroplast is single, parietal, and disposed as part of an equatorial band. Wittrock described the presence of two granule-like bodies of a nutritive character, which he termed "nuclei," situated one towards each end of the cell and outside the chloroplast. I have examined quantities of this plant and find those bodies commonly absent. B. tatrana Wittr. (fig. 25 A — E) which has cells 6 — 9 p, in diameter, occurs in mountain lakes and bogs. It resembles certain stages of species of Tribonema (Conferva), and forms hypnospores (cfr fig. 25 E), but is more rightly placed in the Ulotrichacese on account of its parietal chloroplast. Sometimes the filaments become distinctly mucous. Family 4. CYLINDROCAPSACE.E. This family includes only a few plants belonging to the genus Cylindrocapsa Keinsch. The thallus is filamentous and un- branched, and resembles very much that of certain of the Ulotri- chacea3. The cells are disposed in a single series, each one being surrounded by a lamellose, gelatinous cell-wall, and the entire filament is enclosed in a thick lamellose sheath. The cells resemble very much those of the genus Hormospora in their disposition and they may divide in the same manner as those of Radio/Hum ; they are often ovoid or subtriangular in shape and disposed in pairs at intervals along the filament. Each cell possesses a parietal chloroplast with a single pyrenoid, but it is often difficult to observe the nature of this chromatophore. Asexual reproduction occurs by zoogonidia formed singly, or in twos or fours, from any of the cells of the filament. Each zoogonidium is rounded or oval in form, possesses two cilia, a red pigment-spot and two contractile vacuoles. Sexual reproduction takes place by means of well differentiated male and female gametes. The male organs or antheridia are the result of the active division of certain vegetative cells, and are disposed in one, two, or four longitudinal series within the lamel- lose sheath. Two antherozoids are produced in each antheridial cell, similar in form to the zoogonidia, brownish red in colour, and with two short cilia. The oogonia are developed by an increase in size of the ordinary vegetative cells, each oogonium being large, ovoidal in shape, and with a thick lamellose wall. A single oosphere is present in each oogonium, which opens by a lateral w. A. 6 82 CMorophycece pore to admit the antherozoids. On fertilization the oospore develops a brick-red colour and a thick cell-wall, but it does not Fig. 26. A — D, Cylindrocapsa involuta Beinsch (x480). a, antheridium ; an, antherozoid ; oo, oogonium. (After Cienkowski.) E and F, C. conferta West, from Bowness, Westmoreland ( x 520). fill the oogonium. The method of sexual reproduction was worked out by Cienkowski1. Genus Cylindrocapsa Reinsch, 1867. The thallus consists of unbranched filaments of cells, each cell having a thick lamellose cell-wall. The filaments are encased in a thick lamellose sheath, and they greatly resemble certain of the more gelatinous stages 1 Cienkowski in Bull, de 1'Acad. Imp. St Petersbourg, torn, xxii, 1876, pp. 549 — 555, t. ii, f. 50—65. Chcetophoracece 83 met with in the Ulotrichaceae ; in fact, many authors place this genus in the Ulotrichaceae. Species of this genus are rarely met with in the British Isles. C. involuta Reinsch (which includes C. nuda Reinsch), the cells of which are 23 — 30 p, in diameter, is known from Ireland (fig. 26 A — C) ; C. conferta West (fig. 26 E and F) is known from the English Lake District, and C. geminella Wolle var. minor Hansg. has been observed from Yorkshire and Cambridgeshire. Family 5. CHJETOPHORACEJE. This family of the Chsetophorales has undoubtedly arisen by a further specialization of the Ulotrichaceae. The thallus is branched and the branches are attenuated, sometimes being produced into long multicellular hairs. As a rule the thallus is differentiated into a recumbent or creeping portion, attached to a substratum by rhizoids, and an erect, branched portion. The creeping portion presents a more or less moniliform or torulose appearance, is branched, arid the cells are very similar to those of the Pleurococ- caceae. The cells of the erect portion of the thallus are elongated, more or less swollen, but not torulose, and the branching is most irregular, the terminal cells of the branches frequently forming long hyaline hairs. There is a single chloroplast in each cell, consisting of a parietal, more or less irregular plate, containing one or more pyrenoids. In the attenuated cells towards the ends of the branches the chloroplast becomes reduced, and in the long, hyaline, terminal cells it is entirely absent. Zoogonidia may be produced from all the cells of the thallus except those forming the rhizoids or the terminal hairs of the branches. The number which may arise from a single cell varies from 1 to 16, depending upon the age of the plant, the size of the cell, and other indeterminable causes. Both macrozoogonidia and microzoogonidia are produced, exhibiting a considerable range in size, and they possess either two or four cilia and a pigment spot. They rapidly come to rest, lose their cilia, and germinate directly. On the direct germination of a zoogonidium the cilia are lost, a cell-wall arises, and increase in length takes place, one pole being greatly elongated to form a hyaline, rhizoid-like projection. Septa soon appear dividing the original long cell into several shorter ones, and if the adult plant be a strongly branched one, the 6—2 84 Chlorophycece . / branching soon becomes apparent. The zoogonidia in both tophora and Myxonema (Stigeocloninm) frequently congregate in masses on becoming quiescent and almost all germinate simul- taneously (vide fig. 28 G). Palmelloid groups sometimes arise in Myxonema by the de- generation of some of the branches. Famintzin1 and Fritsch2 have observed these palmelloid cells germinate directly to form new plants, and Cienkowski3 has seen them give rise to microzoo- gonidia, which latter form the young plants. Akinetes( which are rest- ing-cells or hypnocysts) are frequently produced in all the genera of this family. In this condition of the plant almost all the cells of a tuft of branches take part in spore-formation, one rest- ing-spore being formed in each cell. The original cell- walls become hyaline or in- distinct, causing the branch- es to exhibit a moniliform appearance. Each akinete is of a red-brown colour with a thick, asperulate cell-wall (fig. 29 D). The gametes are small biciliated bodies, practically Fig. 27. A and B, Chatophora incrassata indistinguishable from the (Huds.) Hazen, from Scarborough Mere, N. Yorks.; A, nat. size: B, x 500. C, Ch. elegans (Roth) Ag., from Baildon, W. Yorks. (nat. size). microzoogonidia except for the possession of only two cilia, and they conjugate in 1 Famintzin in Melang. Biol. Bull. Acad. St Petersbourg, torn, viii, 1871, p. 265. 2 Fritsch in Beihefte zum Botanischen Centralblatt, 1903, Bd xiii, Heft 4, p. 384. 3 Cienkowski in Botan. Zeitung, 1876, xxxiv. Chcetophoracece 85 pairs. The resultant zygospores usually undergo a short period of rest before germination. Genus Chaetophora Schrank, 1789. The thallus is gelatinous, macroscopic, of a tough consistency, and of some definite form. The filaments radiate out from a central point, those nearest the centre being little branched, but carrying at their apices dense clusters of corymbiform branches of a very bright green colour. The terminal cells of the branches are often prolonged into long hyaline hairs. The zoogonidia possess two or four cilia, and the hypnospores are brown, being generally developed from the terminal cells of the branches. Many of these plants, particularly certain species1, have the power of extracting calcium carbonate from the water in which they live and so giving rise to incrustations of considerable thickness. The most abundant species of the genus is Ch. pisiformis (Roth) Ag., an Alga which occurs as hemispherical, or almost spherical, dark green masses attached to submerged stones or to the submerged parts of plants. It is also often found attached to the shells of aquatic Gastropods. Its distinguishing features are the absence of terminal hairs and the slightly torulose character of cells of the branches; the cells of the primary filaments are 9 — 15 p, in diameter. The next most abundant species is Ch. incrassata (Hudson) Hazen [ = Ch. endivcefolia Ag. ; Ch. Cornu Damce (Both) Ag.], which possesses a tough, gelatinous, sub-dichotomously branched thallus, rather flat and of a darker green at the periphery than in the centre (fig. 27 A and B). The branched thallus bears much resemblance to the horns of a stag and in adult specimens is frequently found floating freely at the marshy margins of poods and lakes, or even in bogs. Ch. tuberculosa (Roth) Ag. possesses a large cushion-shaped thallus from 2 to 4 (or even 5) cms. in diameter, occurring usually in marshes or in bogs. Ch. elegans (Roth) Ag. is a rarer species than the three previous ones and occurs as very pale-green masses, clinging to submerged stems and leaves of grasses, sedges, or mosses (fig. 27 C). Genus Myxonema Fries, 1825. [Stigeoclonium Ktitz., 1843.] The thallus is filamentous, branched, and usually devoid of the great mass of gelatinous material which is so conspicuous a feature of Chcetophora. The branches are scattered, more or less isolated, and often very elongated, but they are rarely developed in dense fasciculate groups. The main branches bear other, shorter, lateral branches which are either acuminate or terminate in long hyaline hairs. There is usually a creeping portion of the thallus, attached to some substratum, but adult plants frequently float freely in 1 Forms of Ch. incrassata and Ch. elegans are often met with encrusted with lime. A form of the latter species was recently named by Tilden Ch. calcarea. Vide Tilden in Botan. Gazette, 1897, pp. 97—100, 102, 86 Chlorophycece ponds and ditches. The macrozoogonidia and microzoogonidia possess two cilia in some species, but four in others1, and they are produced singly or in num- bers from almost all the cells of the thallus (fig. 28 B). The gametes are biciliated (fig. 280 and F) and the zygospores are either smooth or stellate. Iwanoff states that the macrozoogonidia germinate directly, but that the microzoogonidia pass into a resting stage. Fritsch2 has recently published some interesting observations on early stages of development of this genus. He finds the development of the basal portion to vary very much in different species and also to some extent within the limits of each species. He also concludes that cer- tain plants described under the generic name Herpo- steiron are merely stages in the life-history of epiphytic " Stigeoclonia." Hazen3 has given full and conclusive evidence that Myxonema was well estab- lished before the .publication of Kiitzing's genus Stigeoclonium, and sentimental reasons cannot therefore stand in the way of the abandonment of the generic name " Stigeoclonium." There are several British species of this genus, of which the most frequent is M, tenue (Ag.) Rabenh. (tig. 28). M. amcenum (Kiitz.) Ha/en is also another widely distributed species. 1 Iwanoff in Bull. Soc. Imp. Nat. Moscou, 1899. 2 Fritsch in Beihefte zum Botanischen Centralblatt, 1903, Bd xiii, Heft 4. 3 Hazen in Memoirs Torr. Bot. Club, 1902, xi, no. 2, pp. 193—4. Fig. 28. Myxonema tenue (Ag.) Eabenh., from near the Lizard, Cornwall. A, part of thallus (xlOO); B, escape of zoogonidia; C, escape of gametes; D and E, zoogonidia; F, conjugation of gametes; G, development of a cluster of zoogonidia ( x 500). Chcetophoracece 87 Genus Draparnaldia Bory, 1808. The thallus is very gelati- nous, and is differentiated into a principal filament and clusters of lateral branches. The cells of the main filament are large, more or less barrel-shaped, and are furnished with an equatorial, parietal chloroplast with toothed edges. The main lateral branches are alternate, opposite or verticillate, and are themselves very much Fig. 29. Draparnaldia glomerata ( Vauch.) Ag., from Tintagel, Cornwall. A, por- tion of thallus ( x 100) ; B, single cell of main filament showing the chloroplast ( x 220) ; C, part of branch showing escape of zoogonidia ( x 500) ; D, hypno- spores formed from cells of branches ( x 500). branched, the apical cells frequently terminating in long hyaline hairs. From 1 to 4 zoogonidia arise in each cell of the lateral branches (fig. 29 C) and they are furnished with four cilia. They frequently escape through a hole in the cell-wall much smaller 88 Chlorophycece than their own diameter, and they pass through many different shapes in accommodating themselves to this small aperture. Usually all the cells of a single cluster of branches produce zoogonidia simultaneously, the entire performance occu- pying only a few minutes. Resting akinetes (hypnospores) are frequently produced from the cells of the branches. There are two species, D. plumosa (Vauch.) Ag. and D. glomerata (Vauch.) Ag. (fig. 29), widely dis- tributed in the British Islands. They prefer clear water and occur both in the still water of bogs and amongst stones in streams. When growing in streams they are usually found in quiet pools, stretching in long, pale-green, gelatinous strands (up to 20 cms.) from stone to stone. The lateral branches of D. glomerata are fewer and much shorter than those of D. plumosa, the cells are proportionate^ a little longer, and the hairs are also usually longer. The diameter of the primary filaments is 40 — 50 p. and that of the cells of the branches 5 — 10 p. Species of this genus are amongst the prettiest of all freshwater Algae. Genus Pseudochaete West & G. S. West, 1902. The thallus consists of two portions, a creeping portion and an erect portion. The creeping part consists of cylindrical or barrel- shaped cells, about 1^ — 2^ times longer than their diameter, each containing a parietal chloroplast with one pyrenoid. The erect branches arise at right angles to the creeping portion; they are narrower and attenuated to fine points, each one consisting of from five to eight distinct cells. These cells are from 8 to 18 times longer than their diameter and each contains an elongated Fig. 30. Pseudochate .,, • -. gradlis West & G. S. chloroplast, usually without a pyrenoid. West, from near Coates, Sometimes the terminal cells of the branches, Gloucestershire ( x 520). , „ , . or even the two terminal cells, contain no protoplasmic contents and therefore no chloroplast. P. gradlis West & G. S. West (fig. 30) occurs as an epiphyte on aquatic plants. The diameter of the cells of the creeping filaments is 57— Microthamniacece 89 7*7 /x and of the erect branches only 1-5 — 1*8 /*. The plants bear considerable resemblance to Herposteiron Nag. (Aphanochoete A. Br.) but differ in the possession of completely septate branches instead of simple empty bristles. The only other species of the genus is P. crassisetum West & G. S. West which has been found in Ceylon, but it is quite possible that this is merely a developmental stage of an epiphytic Myxonema. Genus Thamniochaete Gay, 18931. The plants of this genus are exceedingly minute, consisting only of three to six cells. They are epiphytic and the basal cell is usually modified to form a hapteron. The terminal cell possesses an elongated bristle or a short spine-like projection. The chloro- plast is parietal and contains one pyrenoid. Th. aculeata West & G. S. West is a rare plant occurring as an epiphyte in the thallus of Gloeotrichia natanfi. It is only known from Connemara in Ireland and from the Hebrides in Scotland. The diameter of the cells is from 5'5 — 13 //, and the terminal bristle is short and very sharp, arising below the apex of a swollen terminal cell (fig. 31 A and B). Th. Hubert Gay is epiphytic on a species of Oscillatoria and is only known from the neighbourhood of Montpellier in France. This genus represents the simplest type of all the Chsetophoraceae — a type in which branching is practi- cally absent. In Th. Hubert the terminal cells are furnished with hollow bristles or hairs exactly as in typical and complex Chaetophoracese. Fig. 31. Thamnio- chcete aculeata West & G. S. West. A, from near Balallan, Outer Hebrides ; B, from Baheh Lough, Galway, Ireland ( x 520). attenuated and are many of the more Family 6. MICROTHAMNIACEJE. The thallus is filamentous, branched, and of small size. The branches are never attenuated into hairs and the cells are some- times moniliform or torulose. The chloroplast is a parietal plate with one or many pyrenoids, or sometimes entirely without them. The zoogonidia are only produced in special swollen cells of the thallus which are differentiated as zoogonidangia. Reproduc- tion frequently takes place by akinetes. It is a small family and bears considerable resemblance to the ChaBtophoracese, being distinguished by the absence of multi- cellular hairs and by the restricted origin of the zoogonidia. It 1 Gay in Bull. Soc. bot. France, torn, xl, 1893, p. clxxvii cum fig. xylogr. 2. 90 Chlorophycece also resembles the Trentepohliaceae but differs in the aquatic habit, smaller size, and in the nature of the chloroplasts. Chodat includes the plants of this family in the Pleurococcaceae. but they have unquestionably reached a higher stage of develop- ment than Pleurococcus or Trochiscia. Genus Microthamnion Nag., 1849 ; Kirchn., 1878. The plants of this genus are at first fixed but afterwards they often float Fig. 32. A — D, Microthamnion Kutzingianum Nag. A — C, young forms from Eichmond Park, Surrey (x500). D, portion of adult form from Horton-in- Eibblesdale, W. Yorks. ( x350). E, M. strictissimum Eabenh., from Blubber- houses, W. Yorks. ( x 500). freely. The filaments are branched and the branches may be short or long. The cells are cylindrical, 3 — 7 times longer than their diameter, and the terminal cells .of the branches are obtuse or Microthamniacece 91 acuminate. The branches all arise immediately below a trans- verse cell-wall, and at first appear as lateral outgrowths from the upper end of a cell. There is also a marked tendency for the branching to be unilateral. The parietal chloroplast is long, entire, and occupies about two-thirds of the inner wall of the cell ; it con- tains no pyrenoids. There are two species, M. Kiitzingianum Nag. and M. strictissimum Rabenh., 1863 [ = M. vexator Cooke, 1882]. The former species (fig. 32 A — D) is much more abundant than the latter, and is most abundant in the early spring. It occurs in small pools and ditches, and likes peat. It is a small, much branched plant, with short branches of one to six cells, the diameter of the branches being 3 — 5 p. M. strictissimum (fig. 32 E) is a larger plant with an erect thallus up to 4 mm. in height. The branches are much longer and more rigid, giving the plant a very different appearance from M. Kiitzingianum. The diameter of the cells is 4 p,. Fig. 32 E is drawn from one of the original specimens sent by W. B. Turner to M. C. Cooke when the latter described the plant as " M. vexator" Genus Gongrosira Kiitz., 1843 [inclus. Pilinia Kiitz. (in part)]. The thallus is attached to a substratum by a mass of parenchyma- tous cells formed by a confluence of creeping branches. From this mass of cells, which may be one or many layers of cells in thick- ness, arise numerous, erect, branched filaments, varying in height from 0'04 to 2 mm. This dense, cushion-like mass of erect fila- ments is frequently incrusted with carbonate of lime, and sometimes forms quite a hard stratum. The cell-walls are often thick and distinctly lamellose. The chloroplast is a parietal plate with one or many pyrenoids, but it is usually difficult of observation. The cells generally present the appearance of being filled with a dense chlorophyllaceous mass, which has been proved to contain starch other than that present in the pyrenoids. The zoogonidia arise in terminal zoogonidangia which are generally flask-shaped. The akinetes are ordinary cells, generally of the recumbent portion of the thallus, which become detached and ultimately form new plants. The plants usually occur at the margins of ponds, lakes, or rivers, forming a tough green stratum on submerged stones or on the shells of aquatic Gastropods. Species of this genus are rare in the British Islands, or perhaps they may have been overlooked. G. viridis Kiitz. is a small species (thickness of prim. fil. 8 — 12 p., of branches 4 — 8 p ; fig. 33 A — C) usually encrusted with lime. G. stagnalis (West) Schmidle is a larger species (thickness of prim. fil. 92 Chlorophycece 16 — 30 p.; fig. 33 D — F) occurring attached to the shells of Limncea peregra. Schmidle has recently given a short systematic account of the genus1. Fig. 33. A — C, Gongrosira viridis Kiitz. (x500). A, from rocks, Lough Beg, Ireland ; B and C, from rocks near Tremethick, Cornwall. D — F, G. stagnalis (West) Schmidle, from near Sutton, Cambridgeshire ( x 200). zg, zoogoni- dangium. Genus Leptosira Borzi, 18832. This genus is scarcely to be distinguished from Gongrosira. The plants are aquatic, forming very minute bright green cushions. The branches are torulose, the terminal cells being elliptical, doliform, or sometimes irregular in form. The cell-contents are pale yellow-green in colour and their structure is exceedingly difficult to observe. The zoogoni- dangia are intercalary and usually consist of the modified, older cells of the plant. The zoogonidia may germinate directly or they 1 Schmidle in Berichte Deutsch. Botan. Gesellsch. 1901, Bd xix. 2 Borzi, 'Studi Algologici I,' Messina, 1883. Trentepohliacece 93 may conjugate in pairs and produce resting hypnospores. In the conjugation of the zoogonidia the ends which do not bear the cilia first fuse together. L. Mediciana Borzi is a rare plant found amongst Sphagnum and Utri- cularia in bogs and boggy pools. It is only known from Yorkshire and Sicily. Diameter of cells up to 20 /x. Family 7. TRENTEPOHLIACEJE. This family is only represented in the British Islands by a few species of the genus Trentepohlia. The thallus is aerial, filamentous and branched, generally occurring on rocks or on the bark of trees. The filaments may be very short and more or less creeping, or they may form erect tufts or closely matted cushions. The cells are sometimes cylindrical and sometimes moniliform or torulose, and the branches usually show a slight attenuation. The cell-walls are firm and frequently exhibit external sculptures. Brand1 states that the longitudinal walls are lamellose, but the transverse walls are simple ; and that the cellulose caps which are so frequently developed at the extremity of a branch, are the remains of dead, terminal zoogonidangia. This is certainly not true of some species, however. Each cell contains one nucleus and usually a number of disc-like, parietal chloroplasts without pyrenoids. The colour of these plants is usually some shade of brown, brownish-red, or orange-red, the chlorophyll being masked by the presence of a pigment known as hsematochromin, which is frequently dissolved in a quantity of oil. In the Trentepohliacese the zoogonidia are only produced in specially differentiated cells or zoogonidangia. This character, the absence of terminal hairs and the nature of the chloroplasts, are the principal distinctions between the Trentepohliaceas and the Chastophoracese. The zoogonidangia are developed singly or in clusters, either terminating a branch and so arresting its develop- ment2, or developed laterally on the branches, or more rarely in the axil of a branch. They are sessile or stalked, generally ellipsoid or ovoid in shape, and they open by means of a terminal or subterminal pore. The zoogonidia, which are of two sizes, are pear-shaped and furnished with two cilia. The smaller micro- zoogonidia have been observed to conjugate in pairs, but all are 1 F. Brand in Beihefte z. Bot. Centralbl. xii, 1902. 2 The development is only arrested temporarily as the terminal cell or supporting cell often grows through the empty zoogonidangium. 94 Chlorophycece capable of direct germination. Resting-spores or hypnospores are sometimes produced. Wildeman1 has shown the ease with which these plants repair injuries to the thallus. Species of this genus are most abundant in damp tropical or subtropical climates, occurring profusely as epiphytes on the leaves and bark of trees. A few of them are constituents of certain tropical lichens. Fig. 34. A — C, Trentepohlia aurea Mart., from Cookridge, W. Yorks. ( x 500). D — F, T. calamicola (Zell.) De Toni, from trees near Lough Gartan, Donegal, Ireland ( x 500). zg, zoogonidangium. 1 Wildeman, in Mem. couronnes et autres Mem. Acad. roy. Belgique, 1899, torn. Iviii. Ulvacece 95 Genus Trentepohlia Martins, 1817. [Chroolepus Ag., 1824.] The thallus is filamentous, simple or ramified. The branches are alternate, of the same diameter as the principal filaments, and do not terminate in a point or hair. The chloroplasts are numerous, discoidal, and without pyrenoids, but are generally masked by the presence of a red or orange-red oil which colours blue with iodine. The most abundant species in the British Islands is T. aurea Mart., which occurs principally in hilly and mountainous districts, forming broad expanded sheets of a bright red or orange-red colour. It is chiefly found attached to rocks, particularly carboniferous limestone or Silurian rocks, and generally on the windward side. The filaments are 10 — 20 p. in thickness (fig. 34 A — C). T. odorata (Ag.) Wittr [=T. umbrina (Kiitz.) Bornet] and T. calamicola (Zeller) De Toni (thickness of filaments 7'5 — 10 p; fig. 34 D — F) are much smaller British species of the genus. Order III. UL VALES. This order is mainly distinguished from the Cha3tophorales by the expanded, parenchymatous thallus, which is attached when young to a substratum by ' rhizoids.' The cells are uninucleate and they contain a single parietal chloroplast, often of considerable bulk and containing one pyrenoid. Asexual reproduction takes place by zoogonidia and also by gemmation. Sexual reproduction is by isogamous planogametes with two cilia. There is only one family which has few freshwater repre- sentatives. Family 1. ULVACEJE. The Algae belonging to this family are more often marine or brackish in habit than freshwater. They consist of flat, ribbon- shaped or expanded plates, or more rarely they exhibit a vesicular or intestiniform structure. These flat or tubular structures consist of one (Monostroma) or two (Ulva) layers of cells which may be somewhat scattered and rounded in form, in which case they are frequently arranged in groups of four, or they may be closely compact with polygonal outlines. The two genera Monostroma and Enteromorpha have freshwater representatives, and in each case the thallus consists of a single layer of cells, division only taking place in one plane. The cells are usually compact and 96 Chlorophycece arranged with their long axes at right angles to the plane of the thallus (fig. 35 D). Each cell contains a single nucleus and one large parietal chloroplast, often with deeply incised or lobed margins and containing a single pyrenoid. In Monostroma bullosa (Roth) Wittr. the cells are generally arranged in T-shaped groups of four. Asexual reproduction takes place in Ulva by zoogonidia (some- times termed megazoospores) with four cilia. These come to rest and germinate directly. Monostroma has been observed to re- produce itself asexually by budding off small flat portions from the surface of the thallus, each portion producing a new plant. Geddes1 has observed a process of gemmation in Enteromorpha. Sexual reproduction is brought about by the conjugation of isogamous gametes. Ordinary cells of the thallus become game- tangia and give rise to eight (sometimes four or sixteen) piano- gametes, which are pear-shaped bodies, smaller than the zoogonidia, with a pigment spot and two long cilia. On conjugation the two gametes coalesce slowly and a " zygozoospore," or a rounded cell with two pigment spots and four cilia, is first formed; this loses its cilia and becomes a zygospore (fig. 35 J). The zygospore usually germinates directly, first forming a short filament of four cells, which soon produce a flat expansion by dividing in two directions in the same plane. According to Reinke the zygospore sometimes becomes a resting-spore or hypnocyst, which on germi- nation divides into four and then eight cells arranged peripherally round a central cavity. By the increase of these peripheral cells a vesicular thallus is produced, which in most instances ultimately becomes a flattened expansion attached by a few rhizoids at its base. Genus Monostroma Thur., 1854. The thallus in the adult plant is always a thin membranaceous plate. In its younger stages it is frequently vesiculose, opening out as it grows into a foliaceous plate, finally becoming free-floating. It consists of a single layer of rounded or more or less angular cells which are often disposed in groups of four. The zoogonidia possess either two or four cilia, and the gametes are biciliated and rather smaller in size. Few species of the genus inhabit fresh water, the only British representa- tives being M. bullosa (Roth) Wittr. and M. membranacea West & G. S. West 1 Geddes in Trans. Koy. Soc. Edinburgh, 1881, p. 555. Ulvacece 97 (fig. 35, A— K). In the former species the cells are rounded, 6—12 p in diameter, and arranged in fours, the two pairs often being disposed in a more or less T-shaped manner. In the latter species the cells are much more compact, angular, and 8 — 20 p. in diameter. Fig. 35. A— K, Monostroma membranacea West & G. S. West, from Mitcham Common, Surrey. A, nat. size ; B and C, portions of thallus showing cells ; D, section of thallus; E, cells with escaping gametes (x566). F — J, con- jugation of gametes (F — H, x 566; I and J, x 790). K, young plant developed from hypnospore ( x 566). L, Enter vmorpha intestinalis (L.) Link, from Frizinghall, W. Yorkshire (nat. size). Genus Enteromorpha Link, 1820. The thallus is elongated, tubular and intestiniform, sometimes reaching a considerable length. It is green, yellowish-green, or pale olive-green in colour, and consists of a single layer of rounded or polygonal cells, each with a parietal chloroplast. The only freshwater species of the genus is E. intestinalis (L.) Link (fig. 35 L), an Alga which also occurs in brackish water and in the sea. It is widely distributed in the large drains and dykes in the east of England, and also occurs frequently in canals and ponds in other parts of the country. W. A. 98 CJdoroptycece Order IV. SCHIZOGONIALES. The thallus is filamentous, sometimes (especially in young stages) parenchymatous, and often expanded into broad sheets by the fusion of the filaments in one plane. The cells are uninucleate with a single central, stellate chloroplast, containing one pyrenoid. The plants are often attached by 'rhizoids' to a substratum, and are subaerial in habit. The order is at once distinguished from the Chsetophorales by its chloroplasts, and by the division of the cells in two, and often in three directions, especially in young plants. From the Ulvales it is distinguished by its chloroplasts, by the more or less regular longitudinal arrangement of the thallus-cells, and by the absence of the vesicular stage in the growth of the young plants. The plants of this order have most probably had a very different origin from the Ulvales, the resemblance being only a parallelism of modification. Family 1. PRASIOLACEJE. This family has been established to include those Algae which are embraced in the Schizogoniales. The thallus is commonly terrestrial, simple and filamentous, or forming flat, creeping expansions. It consists of a single layer of cells produced largely by a fusion of the contiguous walls of cell- filaments. Each cell possesses a central, stellate chloroplast with one pyrenoid. Asexual reproduction takes place by gemmation and by the formation of resting akinetes. Lagerheim has observed the pro- duction of 'tetraspores.' Chodat regards the family as having analogies to the Bangiacese among the Rhodophycese, both on account of the production of tetraspores and the mode of growth. Genus Prasiola Ag., 1821. [Indus. Schizogonium Kiitz. 1843, and Hormidium Kiitz. 1843.] The genus occurs on moist earth, rocks, stones, old walls, trunks of trees, etc. The thallus is filamentous, consisting of one, two, or many series of cells, or foliaceous and expanded with the cells arranged more or less in groups of four. The cells of the ordinary filaments are broader than long and those of the flat expansions are quadrate or polygonal Prasiolacece 99 in form. The cell-wall is strong, rigid and hyaline. The single chloroplast is central, star-shaped, and contains one pyrenoid. Sometimes the thallus is fixed by rhizoids and sometimes not. In the broader, flat expansions the cell-walls are thick and confluent, Fig. 36. A — C, Prasiola pariettna (Vauch.) Wille, from Bradford, W. Yorkshire ( x 500). I) — G, Prasiola crispa (Lightf.) Menegh. ; D, examples from Bradford, W. Yorks. (nat. size); E, simple filament from Helvellyn, Westmoreland; F, portion of irregular filament from Wimbledon Common, Surrey ( x 500) ; G, basal portion of broader thallus, from Bradford, W. Yorks. (x400). and the cells have the appearance of being separated by consider- able spaces. Reproduction is by a process of gemmation, by akinetes liberated at the margins of the thallus, and by tetraspores1. Gay and Chodat separate the genera Schizogonium and Prasiola, but I am inclined to agree with Wille2 in uniting them under Prasiola Ag. Wille and Bb'rgesen3 have each described some interesting marine forms of this genus in which the plants are more amply supplied with rhizoids. The expanded thallus of these forms does not reach such a large size as the thallus of the land forms. Two species are abundant, P. crispa (Lightf.) Menegh. [which includes Hormidium murale Kiitz. ; Schizogonium crispum (L.) Gay ; and Ulothrix radicans Kiitz.], the cells of which are 7 — 14 p in diameter (fig. 36 D — G), and P. parietina (Vauch.) Wille [which includes Schizogonium murale Kiitz. and Hormidium parietinum Kiitz.] with cells 9 — 18 p in diameter (fig. 36 1 Lagerheim, ' Ueber die Fortpflanzung von Prasiola,' Ber. Deutsch. Botan. Gesellsch. 1892, Bd x, Heft 7. 2 Wille, ' Studien iiber Chloropkyceen I- VII,' Vidensk. Skrifter, I math.- naturv. Klasse, 1900, no. 6, p. 13. 3 Borgesen, ' Marine Alg. of the Faeroes,' Bot. of Faeroes, Part II, 1902. 7—2 100 Chlorophycece A — C). These two species are widely distributed all over the British Islands, and they have a decided preference for the neighbourhood of towns, being found frequently under walls and as a green carpet between the paving-stones of quiet streets. They require little moisture and can withstand considerable desiccation. Associated with them are generally numerous Rotifera vulgaris and testaceous Rhizopods such as Trinema acinus. Prasiola furfuracea Menegh. is probably a form of P. crispa. Order V. MICROSPOBALES. This order was first established by Bohlin to include those curious plants which belong to the genus Microspora. It seems at first sight to be giving undue prominence to a small group of aberrant Algae, but at the same time it removes a difficulty, as these plants cannot well be placed in any of the other orders of green Algae. The thallus is filamentous and unbranched, and the cell-walls frequently become broken up into H -shaped pieces. The cells are uninucleate, with a large reticulated chloroplast occupying almost the entire inner surface of the cell- wall, and destitute of pyrenoids. The affinities of the order are very doubtful. Family 1. MICRO SPOR ACE JE. This small family includes only one genus. The thallus is filamentous and simple, and the cells are cylindrical. The cell- walls are composed of cellulose, are either homogeneous or more or less distinctly lamellose, and of a similar structure to those of Tribonema (Conferva), the cells often becoming disarticulated into H -shaped pieces. A single nucleus of considerable size is present in the centre of each cell. The chloroplast is disposed on the walls of the cell and may be band-like or sheet-like, covering more or less the entire cell-wall. It is usually areolated or reticulated, and really consists of a fusion of numerous cushion-like, chlorophyl- laceous masses to form a stout areolated structure. There are.no pyrenoids, but scattered granules of starch are often present. Asexual reproduction takes place by the formation of aplano- spores which become hypnospores (fig. 37 C and F) ; also by the production of biciliated or quadriciliated zoogonidia, one or two of which are found in a cell. Sometimes several small micro- zoogonidia are produced in a cell. The zoogonidia germinate directly. Microsporacece 101 Genus Microspora Thuret, 1850; em. Lagerh., 1888. filaments are simple, con- sisting of cylindrical or slightly swollen cells. The cell-walls are firm, fre- quently distinctly lamel- lose, and sometimes dis- sociating into pieces which appear H -shaped in optical section, each piece consisting of a trans- verse wall and portions of the lateral walls of two adjacent cells. There is one cell-nucleus. The chloroplast is disposed on the cell-walls as a more or less reticulated mass. Globular hypnospores are produced, with thick walls, usually one in each cell. The There are several widely distributed species of this genus in the British Islands. M. floccosa (Vauch.) Thur. and M. amoena(K.\itz.) Lagerh. Fig.37. A, Microspora amcena (Kiitz.) Lagerh., from near Senens, Cornwall. B and C, M. ab- breviata (Rabenh.) Lagerh. ; B from Tremethick Moor and C from St Just, Cornwall. D, M. pachyderma (Wille) Lagerh., from near Land's End, Cornwall. E and F, forms of M. amcena (Kiitz.) Lagerh.; E, from Shipley, W. Yorks., to show the chloroplast; F, from New Forest, Hants, a, aplanospores. (All x520.) E is M. amcena var. crassior Hansg. (fig. 37 A, E and F) are the most abundant and often occur in small ponds and horse-troughs. M. abbre- viata (Rabenh.) Lagerh. (fig. 37 B and-C) and M. pachyderma (Wille) Lagerh. (fig. 37 D) are not so frequent. Order VI. CLADOPHOBALES. In this order are included three families of green Algse which bear close relationship to the Siphoneae and yet can scarcely be relegated to that order. The thallus is simple or branched and incompletely septate, each segment containing many nuclei and numerous parietal chloroplasts, the latter containing single pyrenoids. Asexual reproduction takes place by biciliated or quadriciliated zoogonidia, by 'cysts,' or by special resting-spores (Pithophora) ; 102 Chlorophycece and sexual reproduction is either by isogamous planogametes or by well-differentiated heterogamous gametes. The order includes the following three families : — Family 1. Cladophoracece. Thallus large, branched, incompletely septate, usually attached. Segments large with numerous small chloroplasts, each with a pyrenoid. Family 2. Pithophoracece. Thallus similar to that of the Clado- phoracese, but distinguished by the formation of barrel-shaped and fusiform asexual resting-spores. Family 3. Sphceropleacece. Filaments simple, composed of elongated coenocytes. Sexual reproduction heterogamous; plants monoecious; oogonia with many non-motile oospheres ; fertilization within the oogonium. Bohlin has recently proposed to transfer the families Clado- phoracese (including the PithophoraceaB) and Spha3ropleacese to the order Siphoneas, placing them next the Valoniacese. In this he is followed by Blackman and Tansley, but it yet remains to be shown how far this change is justified. The thallus of the Cladophorales is much more septate than that of the Siphonea3 and the branching is of a different nature. Family 1. CLADOPHORACE^. The thallus is large, filamentous and incompletely septate, each segment being a ccenocyte. The filaments usually have a basal organ of attachment, and in the genus Cladophora are much branched. The growth of the thallus is apical in Cladophora but intercalary in the other genera. There are several nuclei in each segment of the thallus and either one reticulate, parietal chloroplast or a large number of separate chloroplasts, each with a pyrenoid. Asexual reproduction takes place in Cladophora and Chceto- morpha by zoogonidia which are produced in large numbers in the mother-cell and escape either by a terminal or lateral pore. 'Cysts' are also produced in Rhizodonium, each one being a kind of large thick-walled akinete formed from a single segment. An isogamous sexual reproduction occurs in Cladophora, the conjugation of the planogametes resulting in a zygospore which germinates directly without rest. Very little, if any, mucus is secreted by these Algae and they always feel rough and crisp. The absence of a mucous outer coat Cladophoracece 103 causes them to be frequently loaded with epiphytes. Very often the older filaments are thickly covered with Diatoms, particularly of the genera Gomphonema and Cocconeis. Genus Chsetomorpha Kiitz., 1845. The filaments are simple, of more or less uniform thickness and fixed at the base, the lower segments being shorter than the upper ones. The segments are often slightly swollen and they are of considerable diameter. The cell-wall is thick, very firm and obviously lamellose. Most of the species of this genus are truly marine or brackish in habit, but Ch. sutoria (Berk.) Rabenh. (fig. 38) is sometimes found in running water, in wells and horse-troughs, or in streams. Diameter of filaments 100 — 120 /n. Genus Rhizoclonium Kiitz., 1843. The filaments are of vari- Fig. 38. Ch&tomorpha sutoria (Berk.) Eabenh., from Heaton, W. Yorks. ( x 100). able size, crisp, generally branched, and attached at the base by a branched hapteron. The branches are short, slightly attenuated, sometimes merely unicellular outgrowths, but more frequently consisting of several cells. The filaments are often bent at the point of origin of a branch. The cell-walls are firm, lamellose, and sometimes attain a considerable thickness. The number of nuclei present in each segment is variable and the chloroplast is in the form of a network containing several pyrenoids. The most recent account of the structure of this genus is by Wille1, who confirms much that has been described by Gay2. Stockmeyer3 has given a thoroughly good systematic account of the genus. In the autumn the segments of the thallus are often packed with starch. Species of this genus are marine, brackish, freshwater, or they may even occur on damp soil. The only freshwater British species is R. hieroglyphicum Kiitz.; em. Stockm. [ = Conferva fontinalis Berk. ; Microspora fontinalis De 1 Wille, 'Studien iiber Chlorophyceen VII,' Vid.-Selsk. Skrifter. M.-N. Kl. Christiama, 1900. 2 Gay, ' Kecherches sur le d^vel. et la classif. de quelques Algues Vertes,' Paris, 1891. 3 Stockmeyer, ' Uber die Algengattung Ehizoclonium,' Verhandl. der k. k. Zool.-Bot. Gesellsch. in Wien, Jahr. 1890. 104 Chlorophycece Toni] which possesses filaments 10 — 37 /* in diameter and segments 2 — 5 times longer than the diameter (fig. 39 A). The common form of this species pos- sesses no branches whatever and occurs abundantly in ponds, ditches, drains, streams and cataracts all over the country, thriving well in water in which considerable putrefaction is taking place. The following varieties of it are widely distri- buted : — var. Kochianum(Kutz. ) Stockm. [=R.KochianumKi\tz.; R. flavicans Rabenh.], var. tor- tuosum (Kiitz.) Stockm. (fig. 39 B — E), and var. riparium (Harvey) Stockm. Genus Cladophora Ktitz., 1843. This is the best known genus of the family and is widely dis- tributed in salt and fresh waters. The thallus is branched, the type of branching varying with different species, and the segments are 6 — 12 (or even up to 20) times longer than their diameter. There are usually many nuclei in a segment, but they may be reduced to two or even one. The chloroplast is parietal and most commonly reticulate, but all intermediate stages are met with between an elongated reticu- late cylinder and isolated plates1. There is one pyrenoid in each isolated plate or in each corresponding piece of the reticulum. The cell-wall consists of an inner and outer layer, and, according to Brand, of an 'outermost' layer which can be separated by acetic acid. The zoogonidia are very numerous and escape from the mother-cell through an opening formed by a complete absorption of the cell-wall. Nordhausen2 regards the basal branching of the segments in a filament of Cladophora as a peculiar process, to which there is nothing strictly comparable in other Algae. Brand states that the species with strong, primary, basal organs of attach- Fig. 39. A, Rhizoclonium hieroglyphicum Kiitz., single cell showing chloroplast and pyrenoids, from Sheep's Green, Cambridge (x500). B— E, E. hieroglyphicum Kiitz. var. tortuosum (Kiitz.) Stockm., from Heaton, W. Yorks.; B and C, x 100; D and E, x 500. 1 Brand in Beitr. z. Bot. Centralbl. x, 1901. 2 Nordhausen in Pringsheim's Jahrb. f. wiss. Bot. xxxv, 1900. Cladophoracece 105 merit usually form zoogonidia, and that the free-floating species are usually propagated by resting-spores. Fig. 40. B Cladophora glomerata (L.) Kiitz., from Shipley, W. Yorks. A, nat. size ; B, x 85. Most of the species of the genus are marine, but some five or six British freshwater species are known. Cl. glomerata (L.) Kiitz. (fig. 40) is an abundant species, occurring as dark green masses attached to rocks and stones in streams and waterfalls. The branching is dense and the smaller branches are in tufts. Cl. crispata (Roth) Kiitz. is another common species, usually occurring attached to stones. Cl. flavescens Ag. is a more slender species of a pale yellowish-green colour and frequently occurs floating freely in ponds and 106 Chlorophycece Fig. 41. PitJiophora (Edogonia Wittr. var. polyspora Rendle and West f., from the Reddish Canal, near Manchester, A, x 65 ; B — D, frag- ments of thallus with asexual resting spores (as), xlOO. ditches. Brand1 states that all the European species of Cladophora described by Ra- benhorst, except the /Egagro- pilse, must be regarded as varieties, forms, or conditions of Cl. fracta or Cl. glome- rata. Genus Chsetonella Schmidle, 19012. This genus was instituted for the reception ' of a small, almost microscopic plant, which occurs either free-floating or attached to the mucous coat of other larger Algse. It is incompletely septate, and each segment possesses from two to five nuclei. The segments are cylin- drical or more or less ir- regular, and the thallus is branched. The branches are attenuated and the terminal cells are of greater length than the others. There is one parietal chloroplast with- out pyrenoids. There is only one species, Ch. Goetzei Schmidle, which is known from tropical Africa and from West Yorkshire. The filaments are 6 — 8 p. in thickness. Family 2. PITHOPHORACE^E. The plants of this family very much resemble species of the genus Cladophora. The thallus is of exactly the same type and the 1 Brand in Bot. Centralbl. Ixxix, 1899. 2 Schmidle in Engler's Botan. Jahrbiich. Bd 30, Heft 2, 1901, p. 253, t. v, f. 1, 2. Pithophoracece 107 growth is apical. The thallus is almost always branched, the branches arising a little below the top of their supporting cells, and it is attached below by well-developed haptera put out from a basal cell. It is doubtful if there is sufficient evidence to warrant the separation of the Pithophoraceae as a distinct family from the Cladophoracese . Asexual resting-spores are produced here and there in the thallus, either intercalary and cask-shaped, or terminal and ovoidal or fusiform. These spores, which were termed by Wittrock 'agamo- spores,' are richly filled with chlorophyll and the spore-wall increases considerably in thickness. Formation of spores may take place in all the cells of the cauloid part of the thallus. After a short period of rest the spores develop in opposite directions from the two apices. There is another method of asexual reproduction by ' pro- lific cells.' Genus Pithophora Wittr., 1877. This striking genus of Algae is almost exclusively tropical in its distribution. It is the only representative of the family, and few Algae are more characteristic than a plant of Pithophora with ripe spores. P. (Edogonia (Mont.) Wittr., var. polyspora Rendle and West f.1 (fig. 41) may be regarded as a British Alga, having been found in the Reddish Canal, near Manchester. P. Kewensis Wittr. occurred in a tank in the water-lily house, Kew Gardens, but was most probably introduced from tropical S. America. Family 3. SPIOEROPLEACEJE. This family includes only one Alga, which occurs in extensive masses on flooded plains and by the margins of lakes. The filaments are cylindrical and unbranched, and consist of single series of coenocytes which reach an extraordinary length as com- pared with their breadth. The transverse cell-walls often become of great thickness, and each segment of the filament contains a considerable number of small nuclei. The chloroplasts, which are in the form of parietal rings, are very numerous and some of them contain pyrenoids. The sexual organs are oogonia and antheridia, which may be formed without change of shape from any segment of the filament. Sometimes the oogonia and antheridia alternate in a filament, but 1 A. B. Eendle and W. West, junr., 'A New British Freshwater Alga,' Journ. Bot. July, 1899, pp. 289—291, t. 399. 108 Chlorophycece more often they do not. A number of oospheres are developed in each oogonium, and a very large number of antherozoids arise by the breaking up of the red contents of an antheridium. The antherozoids are small, elongated bodies, provided with two long cilia, and they find their way into the oogonia through apertures in the transverse walls. After fertilization, which takes place within the oogonium, the oospores develop a thick verrucose cell-wall and the cell-contents become bright red in colour. The oospores generally hibernate within the oogonium, and this is the most striking condition of the Alga, which now consists of long filaments, most of the segments of which are filled with numerous, bright red, verrucose oospores. On the germination of the oospore from two to eight zoospores are set free, representing the sporophyte generation, and each of these forms a new plant. The young plants are simple,, fusiform cells, with each extremity attenuated to a very fine point. Bohlin has suggested the transference of this family to the order Siphonese in close proximity to the family Valoniaceae. Genus Sphseroplea Ag., 1824. The thallus consists of un- branched filaments of cylindrical coenocytes, which may only be as long as their diameter or up to ninety times longer. The filaments are 36 — 72 /u, in diameter. The only known species — Sph. annulina (Roth) Ag. — is not a British Alga. It occurs extensively on inundated portions of the plains of Europe, Asia and America, and is sometimes found in pits or quarries. It is question- able if there are any suitable localities for this plant in the British Islands. It sometimes occurs in Kew Gardens, having been introduced from abroad with various aquatic plants. Order VII. SIPHONED. The order Siphonese embraces a large number of filamentous Algse of many diverse forms. They are cosnocytic in character, the individuals being without septa, so that in reality each plant consists of a single large coenocyte. They are mostly marine Algae and some of them attain a considerable size. The thallus fre- quently becomes very complicated in character, but even then it consists of the interlaced branches of a single multinucleated cell. Nowhere else in the vegetable kingdom do such gigantic cells occur, and it is this extraordinary complication of a single cell which distinguishes the Siphoneae from all other Alga?. Many of Vaucheriacece 109 them have even reached a high stage of specialization, having developed organs analogous to the stem, leaf and root of higher plants. In the genus Caulerpa the cell is strengthened by trabe- culse which traverse the lumen of the cell from wall to wall. Asexual reproduction takes place by proliferous shoots, by non-ciliated spores and by zoogonidia. In most of the Siphonese numerous zoogonidia arise in a zoogonidangium, but in Vaucheria only one large one is produced. The plants are generally attached by strongly developed haptera. The only family of the order which inhabits fresh waters is the Vaucheriaceae, and it is also the only family in which well- differentiated sexual organs occur. The tropical family Phyllo- siphonaceae includes a number of Algae which live as parasites on the leaves of Phanerogams. Family 1. VAUCHERIACEJE. The thallus is an elongated filament consisting of a single large ccenocyte, and is sometimes branched. This unseptate filament increases in length by apical growth and is usually attached to a substratum by much branched haptera. In most members of the family the cell-wall is thin and relatively weak, easily collapsing even with careful manipulation. The protoplasm forms a thick lining layer on the interior of the wall of the filament and contains a large number of minute nuclei. The chloroplasts are very small and exceedingly numerous ; they are oval, elliptical or subcircular in outline and are without pyrenoids. A considerable amount of oil is often present in the filaments, the oil-drops being always in connection with the chloroplasts. Fleissig1 states that this oily material is a reserve substance, physiologically analogous to starch. On the injury of the thallus septa usually appear cutting off the injured parts, the uninjured portions developing into new plants, (vide fig. 42 A and B.) These are the only instances of the occurrence of septa in the thallus except in connection with the reproductive organs. Asexual reproduction takes place by the formation of zoogonidia. The extremity of a filament assumes a club-shaped form and becomes densely filled with protoplasm, after which a transverse 1 Fleissig, 'Ueber die phys. Bedeutung d. oelartigen Einschliisse in d. Vaucheria,' Basel, 1900. 110 Chlorophycece septum appears and cuts off the swollen end as a zoogonidangium. The contents of this gonidangium, which are of a rich green colour, gradually become rounded off, forming an oval zoogonidium of large size. The whole surface of the zoogonidium is usually clothed with numerous short cilia, arranged in pairs, and in the surface protoplasm under each pair there is a small nucleus. The entire structure contains one central cavity filled with cell-sap Fig. 42. A and B, portions of thallus of Vaucheria showing formation of septa on injury; A, Vaucheria geminata (Vauch.) D. C.; B, V. sericea Lyngb., from Harefield, Middlesex. C, apex of filament of V. sessilis (Vauch.) D. C., show- ing the zoogonidangium from which will escape a single zoogonidium. D, ger- mination of the zoogonidium of V. sericea, from E. Yorkshire. E, V. sessilis from W. Yorkshire, showing developing oogonium (on right) and antheridium (on left). F — H, V. geminata (Vauch.) D. C., from Barnes Common, Surrey, showing development of sexual organs. (All x 75.) a, antheridium, 06, oogo- nium; zg, zoogonidangium. which is traversed by strands of protoplasm, and Schmitz has pointed out that it can be looked upon as an aggregate of zoogonidia with a great resemblance to certain of the more complex members of the Volvocaceae. This compound zoogonidium escapes by an apical opening of much smaller diameter than itself and through which it pushes its way. Sometimes, owing to the rotatory movement of the cilia, the part first exuded becomes separated from the portion still left in the gonidangium and two zoogonidia are formed instead of one. The zoogonidia generally escape in the morning, that is to say, after the plants have been in the darkness for some time. They Vaucheriacece 111 are sluggish in their movements and continue active for about fifteen minutes. On coming to rest the cilia are at once withdrawn and a cell- wall is developed. Klebs1 states that zoogonidia can always be produced when filaments which have been kept moist for some days are soaked with water, or when they are removed from a dilute nutritive solution into pure water. The zoogonidia germinate almost immediately by the protrusion of one or more tube-like filaments, one at least of which attaches itself to the substratum by a colourless branched hapteron (or 'rhizoid'). Under unfavourable circumstances, particularly if the plants are liable to become dried up, asexual spores of another kind are sometimes developed. The end of a filament swells up into a more or less globular form and then a transverse wall appears and cuts this portion off. Such a spore may rest a considerable time before germination. Sometimes, owing to drought, certain filaments break up into a number of distinct ccenocytes, each of which develops a thick cell- wall. These are of the nature of rudimentary gemmae or cysts2. Sexual reproduction takes place by oogonia and antheridia, and amongst the Siphonese this family of Algse stands alone in the possession of sharply differentiated sexual organs. These are developed at scattered intervals along the cylindrical filament. Except in the dioecious plants the antheridia and oogonia usually arise side by side on the same filament, or they are differentiated portions of a short lateral branch. The oogonia usually arise as lateral outgrowths of the filament, or at the end of a very short branch, and they soon assume a more or less rounded or ovate form, being ultimately cut off by a septum at the base. The apex of the oogonium generally develops a rostrum or beak, which is usually turned to one side, either towards the antheridium or away from it. The protoplasm of the oogonium 1 Klebs, 'Die Bedingungen d. Fortpflanzung bei einigen Algen u. Pilzeti,' Jena, 1896. 2 Bennett and Murray in their 'Handbook of Cryptogamic Botany,' London, 1889, p. 284, in referring to this special type of asexual reproduction in Vaucheria, state that "in this condition it was formerly described as a distinct organism under the name of Gongrosira." Dr Scott, also, in his ' Introd. to Structural Botany, Part it,' London, 1897, remarks that "this is called the Gongrosira state, because specimens of Vaucheria in this condition used to be placed in a different genus under that name." These are most unfortunate statements, as Gongrosira is a well-established genus of the Chsetophorales, which reproduces itself asexually by minute biciliated zoogonidia, and none of the plants of which approach in size even the smallest known species of Vaucheria. 112 contains a considerable amount of oil, numerous chloroplasts, and after the appearance of its basal wall, only one nucleus. That portion of the protoplasm towards the apex or beak becomes clear and free from chloroplasts, and is termed the receptive spot. The cell-contents now become rounded off, forming the ovum (or Fig. 43. A and B, Vaucheria sessilis (Vauch.) D. C. ; A, from Esher West-end Common, Surrey; B, from Mitcham Common, Surrey. C and D, V. hamata (Vauch.) Lyngb., from Calverley, W. Yorks. E, oogonium and oospore of V. sericea Lyngb., from Beverley, E. Yorkshire. (A — D, x200; E, x320.) a, antheridium ; an, antherozoid; oo, oogonium. oosphere) and soon afterwards the wall of the oogonium opens at the extremity of the beak, a small quantity of mucilaginous pro- toplasm being exuded. The antheridia develop simultaneously with the oogonia and generally in close proximity to them. (Fig. 42 E.) Each anthe- ridium arises as a short cylindrical branch which usually becomes much curved on approaching maturity. (Fig. 43 A and B.) The terminal portion of this curved branch is cut off by a septum and becomes the actual antheridium. In some species, such as in the submarine Vaucheria synandra, a number of antheridia occur on a structure known as an " androphore." The protoplasm of each antheridium contains numerous chloroplasts and nuclei. The nuclei collect in the central portion of the antheridium and it is Vaucheriacece 113 this part which breaks up into the antherozoids (or spermatozoids). The latter are extremely minute, each one consisting of a small amount of protoplasm surrounding a nucleus and possessing two cilia. The cilia are attached far apart and point in opposite directions. (Fig. 43 A, an.) The antherozoids swarm for a short time within the antheridium, which soon opens at the apex and sets them free. A certain amount of unused protoplasm is expelled with the antherozoids and another portion is left behind in the antheridium. The antherozoids swarm near the opening of any oogonium they may happen to reach and frequently several of them enter the oogonium. One of them fuses with the oosphere at the region of the receptive spot and its nucleus travels through the protoplasm of the oosphere until it reaches the single nucleus of the latter. The male and female nuclei then unite and fertilization is effected. The fertilized ovum or oospore now invests itself with a cell- wall of considerable thickness and undergoes a prolonged rest. The oospores can withstand a certain amount of desiccation, and on germination they give origin to a new plant without any alternation of generations. Genus Vaucheria DC., 1803. This is a widely distributed genus of Algse the filaments of which are interwoven to form compact, mat-like masses, either on damp earth, or in fresh or salt water. They most commonly occur in situations where they are subject to the splashing or trickling of water, although some habitually occur on damp ground or are entirely submerged. They are most abundant in the earlier months of the year. The filaments are coarse and thick, consisting of large coenocytes, which some- times reach 30 cms. in length, and their numerous chloroplasts give them a dark green colour. They are very sparsely branched, and some species rarely exhibit any branching except in connection with the formation of the sexual organs. Dioecious species of the genus exist, but in most others the antheridia and oogonia are developed in close approximation on the same filament. The filaments are sometimes subject to the attacks of the Rotifer Notommata Werneckii, which produces irregular gall-like swellings. V. sessilis (Vauch.) DC. is perhaps the commonest species of the genus, being widely distributed in damp and wet situations in the neighbourhood of streams, cataracts and boggy springs ; thickness of filaments 65 — 80 p (figs. 42 C and E ; 43 A and B). V. geminata (Vauch.) DC. also occurs in similar W. A. 8 114 Chloro})hycecK localities ; thickness of filaments 78 — 90 p. (fig. 42 A, F — H). V. terrestris Lyngb., and V. hamata (Vauch.) Lyngb. (fig. 43 C and D), occur in profusion on damp ground, often forming thick mats on gravel paths and on the surface soil of damp flower-pots. V. sericea Lyngb., which is the smallest British species (thickness of fil. 48 — 55 /u, ; fig. 42 B and D, 43 E), and V. aversa Hass. usually occur entirely submerged in the waters of ditches and ponds. V. dicho- toma (Lyngb.) Ag. is the largest British species (thickness of fil. 180 — 220 ^) and is dioecious. Some forms of it are truly marine, but others occur in brackish water. Order VIII. CONJUGATE. The order Conjugatse is one of the best defined and most natural of the groups of the Chlorophycese. The thallus is unicellular in the Desmidiacese and the individuals exhibit great specialization of form. In the Zygnemacese, which is the only other family of the order, the plants are multicellular, consisting of unbranched filaments of cylindrical cells. These filaments are, however, fragile and often become dissociated into their individual cells. All the plants of this order, whether unicellular or multi- cellular, are remarkable for the great development of the gelatinous pectose constituents of the cell-wall. There appears to be a continual exudation of this gelatinous material, until, in some instances, it is of much greater bulk than the individual plant, and it frequently happens that the unicellular forms occur embedded in a mass of transparent jelly formed by the coalescence of their outer gelatinous coverings. One of the most conspicuous features of the order is the presence of chloroplasts of large size and definite form. They vary in number from one to about eight or twelve in each cell and they exhibit great variety in form and symmetry. Each chloroplast contains one or more conspicuous pyrenoids. Boubier1 has observed in species of Spirogyra and in Mouyeotia scalaris Hass. what he terms ' compound pyrenoids.' These consist of an agglomeration of pyrenoid structures enclosed in a membrane and containing in the centre a pyrenocrystal. Multiplication of the filamentous forms sometimes takes place by the fragmentation of the filaments, each cell undergoing rapid division and forming a new plant. Asexual reproduction may be brought about in the Zygnemacese 1 Boubier in Bull. Herb. Boissier, vii, 1899. Conjugatce 115 by the formation of resting-cells with thick walls, which have received the name of ' cysts.' These are capable of surviving the winter. In both the Zygnemaceae and Desmidiacese aplanospores are sometimes formed. Zoogonidia are entirely absent from this order of green Algae. Sexual reproduction takes place by the conjugation of isogamous gametes and the formation of a zygospore. As the gametes are devoid of cilia and therefore non-motile, they are known as aplano- gametes. The ordinary vegetative cells become the gametangia, usually without change of form, and only one gamete arises from a gametangium, the entire cell-contents of which are generally utilized in its formation. In the Desmidiaceae (with a solitary exception) the gametes are set free and conjugation takes place outside the gametangia, but in the Zygnemeae the gametes unite either within one of the gametangia or within the connecting-tube which joins them. In these groups the zygospore after a period of rest forms a new gametophyte, but in the Mesocarpeae the zygospore immediately forms a rudimentary sporophyte with one spore (a carpospore) ; the latter undergoes a long rest. Much has been written concerning the sexuality of the Con- jugatae, and much of the evidence which has been brought forward of late years indicates that sexuality of a low type does exist. This sexuality is less marked in some Conjugates than in others, and least of all in the Desmidiaceae. The cells in a filament of Zygnema or Spirogyra need not necessarily be considered as. all of the same sex. It is quite possible that they have no sex until just prior to conjugation. There is no visible change on the conversion of an ordinary vegetative cell into a gametangium ; the change is a physiological one which most probably takes place immediately antecedent to conjugation, and the formation of a male or a female gametangium may depend upon restricted local conditions. Taking this into consideration, it is no more surprising to see both male and female gametes produced from the cells of a single filament than to see a filament which gives origin to gametes of one sex only. It has been shown that a strictly filamentous condition is of no essential importance to the life of the Conjugate, and also that the functional activities of the cells of a filament are greatly increased during conjugation, even in those cells which take no part in the actual conjugation1. Thus, there is no reason why the physiological 1 West & G. S. West, ' Obs. on the Coiij.,' Ann. Bot. xlv, 1898, pp. 30, 36, 37. 89 A 116 ChloropTiycecK changes which take place in a filament on the conversion of its vege- tative cells into gametangia — changes which are rendered manifest by a general increased activity — should not be so far modified at different parts of the same filament as to produce a differentiation of sex. This affords an explanation of the rare cases of " cross- conjugation" to be described later on, but at the same time there is no doubt that it is a general rule in the Zygnemese that the cells of any one filament all become of the same sex. Little is known concerning the effect of temperature and climatic conditions on the methods of reproduction of the Conjugate. A high altitude, which is usually accompanied by a relatively low temperature, certainly favours the formation of 'cysts,' and an increase of temperature is in many cases an aid to conjugation. With regard to the British Islands, conjugating examples of the Zygnemaceae are more frequently met with in low-lying areas than in upland districts, and most frequently in the western or south- western counties. Observations tend to prove that the Conjugatse in their natural habitats withstand extremes of temperature very well, and that they are capable of adapting themselves to very different conditions from those under which they normally exist. All plants of this order, whether unicellular or filamentous, are very slimy to the touch. This is due to the gelatinous nature of the outer layers of the cell-wall, and this character alone frequently enables the collector to distinguish Conjugates from most other filamentous green Algae. The order is subdivided into three families, of which one — the Temnogametacese — is only known from Equatorial Africa. The two British families are : — Family 1. Zygnemacece. Thallus filamentous, consisting of a single series of cylindrical cells, each cell possessing one or several chloroplasts of definite form. Any cell may become a gametangium. Family 2. Desmidiacew. Thallus unicellular ; cells sometimes loosely, sometimes closely joined into simple filaments, in most genera constricted into two equal and symmetrical halves. Chloroplasts one or several in each cell, usually of definite form. Many of the plants of this family are remarkable for their beauty of form. Any cell may become a gametangium. Family 1. ZYGNEMACEJE. This family of Conjugates has a world-wide distribution and includes some of the commonest and most striking of freshwater Algse. The thallus is in every instance filamentous and consists of Zygnemacece 117 a single series of cylindrical cells forming an unbranched filament. Rare instances of branching are known, but the branches have been limited to short lateral outgrowths consisting only of a few cells ; such outgrowths have been observed in the genera Zygnema and Mougeotia1. Similarly, longitudinal septa of an incomplete character have been observed in Zygnema pachydermum West, var. confervoides West2. Rhizoid-like organs of attachment or haptera are of frequent occurrence in young plants of Spirogyra and Mougeotia, but have not been noticed in any of the other genera of Zygnemaceas. They are usually simple or branched outgrowths near the base of the filament, but in Spirogyra they may arise by the modification of a conjugating- tube which has been protruded by a cell some distance removed from those cells actually engaged in conjugation. This is yet another proof of the increased activity of the filament as a whole during conjugation. The ZygnemaceaB is divided into three sub-families, of which the PyxisporeaB is only known from tropical Africa. The two British sub-families are: — Sub-family 1. Mesocarpece. Conjugation forming a zygospore which immediately develops a sporocarp of several cells, one of which is the spore (carpospore). The gametophyte is developed from this spore after a period of rest. Sub-family 2. Zygnemece. Conjugation producing a zygospore which after a period of rest develops directly into a new gametophyte. Sub-family I. MESOCAEPEJE. The plants of this sub-family are the narrowest and most delicate of the filamentous ZygnemaceaB. There is a great varia- bility in the diameter and relative length of the cells, and the cell-wall is relatively thin. The cells contain a single chloroplast, generally in the form of a thin axile plate, which may extend from end to end or only occupy the median portion of the cell. Each chloroplast contains several pyrenoids arranged in a single longi- tudinal series. The chloroplasts of adjacent cells usually lie in the same plane, so that a whole filament of cells may exhibit the full breadth of the chloroplasts or it may be in a position such that only the thin edge of the chloroplasts can be seen. The action of light causes a rotation of the plate-like chloroplasts of Mougeotia. 1 West & G. S. West in Ann. Bot. 1898, xlv, p. 32, t. iv, f. 17, 18, 19 and 41. 2 West, ' Alg. from the W. Indies,' Journ. Linn. Soc. Bot. xxx, t. xiv, f. 5. 118 Chlorophycece In diffused daylight they place themselves at right angles to the direction of the incident rays, but in strong sunlight the edge of the plate is directed towards the light. This has long been known to students of Alga3 and special mention of it was made by Bennett. Quite recently this phenomenon, which is well exhibited by the chloroplasts of many green plants, has been further investigated and it has been shown that the chloroplast occupies on an average about 30 minutes in rotating through 900.1 Apart from the lining layer of protoplasm and the chloroplast, a considerable proportion of the cell-cavity is usually occupied by large fluid vacuoles. Vegetative multiplication frequently occurs by the dissociation of a filament into its constituent cells, each of which forms a new plant by rapid cell-division. Asexual reproduction takes place occasionally in Mougeotia by the formation of spores resembling aplanospores2. These spores are produced by the division of a vegetative cell and they may be regarded as carpospores formed from sporocarps (consisting of three cells) produced without conjugation, but possibly in consequence of the stimulus which has already caused conjugation to take place in a distant part of the filament. In the genus Gonatonema repro- duction is solely by the formation of aplanospores, the whole of the contents of a single cell being generally, but not always, utilized in the formation of a spore. It has been noticed in the three best known species of Gonatonema (viz. G. ventricosum Wittr., G. Bood- lei W. & G. S. West, and G. tropicum W. & G. S. West) that during the formation of the spore, and just before the rounding off of the protoplasmic mass, there is sometimes a more or less complete division of the cell-contents into two parts3. I have care- fully studied the formation of aplanospores in this genus and this curious separation of the cell-contents into rudimentary gametes is by no means of frequent occurrence. It is most likely a slight retention of the last traces of ancestral sexual characters, the spores having arisen at one time by a process of conjugation. Sexual reproduction of a low type takes place in Mougeotia by conjugation. This almost always occurs between the cells of different filaments which are lying side by side. Each cell puts 1 F. J. Lewis in Ann. Bot. xii, 1898. 2 Wittrock, 'Om Gotl. och 01. Sotv. Alg.,' Bihang till K. Sv. Vet.-Akad. Handl. Bd 1, no. 1, 1872, t. ii, f. 7 and 8. 3 W. & G. S. West in Ann. Bot. 1898, xlv, p. 39, t. iv, f. 3; Trans. Boy. Irish Acad. xxxii, sect. B, 1902, p. 17, t. i, f. 5. Zygnemacece 119 out a protuberance on the side towards the other filament, and this meets with a similar protuberance from one of the opposite cells. The ends of the protuberances fuse together and an open tube is formed placing the two conjugating cells in communication with each other. This is known as the conjugating -tube. During the development of the protuberances and their ultimate fusion the greater part of the protoplasmic contents of each cell, including the chloroplast, contracts away from the wall of the gametangium and passes into the conjugating-tube. There, a coalescence of the gametes takes place, resulting in the formation of a zygospore, which, although a compact mass situated in the conjugating-tube, is not at first cut off from the rest of the protoplasm left in the gametangia. Wittrock regards the entire H -shaped structure, consisting of the two gametangia and the conjugating-tube, as the zygospore. Cell-walls soon appear in this structure, indicating the formation of a rudimentary sporocarp, and they cut off a central fertile carpospore from the surrounding sterile cells (two, three, or four in number). Thus, the Mesocarpese afford an instance in the green Algae of a sporophyte generation and a rudimentary ' alterna- tion of generations.' The method of spore-formation met with in Mougeotia differs materially from that which occurs in the Zygnemeas. The spore is not formed by the development of a new cell- wall around the fused gametes, but by the appearance of partition walls which cut off some part of the H -shaped structure in which fusion of the gametes has taken place. Thus, the spore in the Mesocarpea? can be re- garded as a carpospore which is bounded partly by new walls and partly by the walls of the gametangia or the conjugating-tube. The type of conjugation between the cells of distinct filaments is known as scalariform conjugation. In some cases conjugation occurs between adjacent cells of the same filament. This type is known as lateral conjugation, and although commonly met with in the Zygnemea3, is very rarely observed in the Mesocarpese. Irregularities are sometimes met with in the conjugation of Mougeotia. Cases have been observed in which the terminal cell of a filament has entered into conjugation through its free end, no conjugating-tube being developed, and rare instances occur in which three cells, each belonging to distinct filaments, have entered into conjugation. Equally rare are the hybrid examples in which conjugation has occurred between species of Mougeotia of different 120 Chlorophycece thickness. Two carpospores have been observed to be formed in one sporocarp of Mougeotia capucina ; this is precisely analogous to the double spores met with in certain Desmids and in abnormal cases of Spirogyra. Fig. 44. A, Mougeotia sp., from Frizinghall, W. Yorks., young filament showing organ of attachment ( x 100). B, Mougeotia capucina (Bory) Ag., from the New Forest, Hants., showing edge of plate-like chloroplast ( x 430). C, M. viridis (Kiitz.) Wittr. ( x445). D — H, M. parvula Hass. ; D — F, from Epping Forest, Essex ; G and H, from near Settle, W. Yorks. ( x 445). I, M . gracil- lima (Hass.) Wittr., from Esher West-end Common, Surrey ( x 445). cp, carpo- spore ; sp, sporocarp; z, zygospore (of Wittrock). Zygnemacece 121 Indications of sexuality are to be found in the Mesocarpese, but they are much less marked than in the Zygnemese. The spores are often seen to be situated nearer to one gametangium and the conjugating- tube of that gametangium to be thicker and shorter than that of the other ; hence the former may be looked upon as a female cell and the latter as a male cell. As these indications of sexuality are scarcely discernible and often absent, the Mesocarpese may be regarded as having lost almost all traces of differentiation of sex. Genus Mougeotia Ag., 1824. [Staurospermum Klitz., 1843 ; Mesocarpus Hass., 1845 ; Craterospermum Braun, 1855 ; Plagio- spermum Cleve, 1868.] The thallus consists of cylindrical un- branched filaments of elongated cells. The single chloroplast is disposed_as an_axjle plate, extending from end to "ehcToTtne cell or only occupying the median portion. The jjiyrenoids are numerous and usually arranged in a single series. In ]ft. capucina the • chloroplast sometimes assumes the form of an irregular axile rod, connected with the lining layer of protoplasm by fine colourless strands, and the vacuoles contain a purple cell-sap. In some species the carpospores are spherical, but in others they are quad- rate and more or less flattened, with rounded or truncated angles. Species of this genus were at one time referred to various genera, such as Mesocarpus, Staurospermum, etc., according to the disposi- tion of the sterile cells of the sporocarp and the form of the carpo- spores, but all the supposed generic differences have been found by Wittrock to be present in one and the same filament of Mougeotia calcarea Wittr. Throughout the entire genus there is great variability in the relative size of the carpospore and the sterile cells of the sporocarp. In mountain tarns and lakes species of this genus are extremely abundant, and they flourish in the summer months in small pools on the mountains up to 3,000 ft. elevation. In these situations the plants rarely conjugate and they are kept alive through the winter largely by the formation of resting-cells or ' cysts,' which are of the same form as the ordinary vegetative cells. In the plankton of large lakes the filaments are often much twisted and coiled. There are about 15 British species of the genus, of which M. scalaris Hass. (diameter of fil. 32 — 35 /*) is the largest and M. elegantula Wittr. (diameter of fil. 3'5 — 4'5 fi) is one of the smallest. The two most abundant species are 122 Chloropkyeece M. parvula Hass. (fig. 44 D — H) and M. gracillima (Hass.) Wittr. (fig. 44 I), which conjugate freely in all parts of the country and at all elevations up to 1,200 ft. M. genuflexa (Dillw.) Ag. is a frequent species in ditches and ponds. M. gelatinosa Wittr. is one of the rarest British species, being characterized by the curious gelatinous investment of the carpospore. Genus Gonatonema Wittr., 1878. The thallus is similar in all respects to that of Mougeotia, but the reproduction is brought about solely by the formation of aplanospores, the filaments usually becoming genuflexed at the points of location of the spores. Each Fig. 45. A— F, Gonatonema Boodlei W. & G. S. West, from Mitcham Common, Surrey. G — J, G. ventricosum Wittr., from the river above Crolly Bridge, Donegal, Ireland. (All x 445.) a, aplanospore. Zygnemacece 123 spore is formed by the rejuvenescence of the contents of the mother-cell, and there is a greater difference in size between the spores of species of this genus than can be accounted for by the difference in cubical capacity of the mother-cells. Plants of this genus are of much rarer occurrence than those of Mougeotia ; in fact, they are amongst the rarest of the Conjugatse. G. notabile (Hass.) Wittr., with vegetative cells 12 — 15 p. in diameter, has not been seen since its discovery by Hassal in 1845. G. ventricosum Wittr. (fig. 45 G — J), with veg. cells 7'5 — 8'6 p in diameter, is known from Ireland; and G. Boodlei W. & G. S. West (fig. 45 A — F), with veg. cells 5 — 5 '5 /* in diameter, has been found in Surrey. The aplanospores of G. ventricosum are likewise considerably different from those of G~ Boodlei and they are sometimes produced by the swelling of the free end of the terminal cell of a filament. Sub-family II. ZYGNEME^E. The plants of this sub-family consist of unbranched filaments of cells similar to those of the Mesocarpese, but usually of much larger size. There is a lining layer of protoplasm in each cell and the nucleus is situated in the central portion of the cell, embedded in a mass of protoplasm which is connected with the lining layer by numerous radiating strands. Gerassimoff1 finds certain cells of Spirogyra majuscula to contain two ordinary nuclei or one com- pound nucleus. The chloroplasts, which contain prominent pyre- noids, are somewhat variable in form and disposition ; in Debarya there is a single axile plate similar to that of Mougeotia', in Zygnema there are two star-shaped chloroplasts suspended in the middle line of the cell; and in Spirogyra the chlorophyll is arranged in one or more bands twisted spirally round the interior of the cell- wall. The chloroplasts of Spirogyra are very variable and special reference is made to this feature under the genus. Vegetative multiplication takes place as in the Mesocarpese by the breaking up of a filament into its constituent cells, or into groups of cells, which then grow into new filaments. Asexual reproduction sometimes takes place by the formation of aplanospores, which are produced from the contents of a single cell. They are more frequently found in Zygnema than in Spiro- gyra, and until the discovery of Z, spontaneum Nordst. in West Africa2, the only known method of reproduction of this species was 1 Gerassimoff in Bull. Soc. Imp. Nat. Moscou, 1897. 3 W. & G. S. West in Journ. Bat. Febr. 1897, p. 15. 1 24 Chlorophycece an asexual one1. The aplanospores (or, as they are frequently termed, ' parthenospores ') of Zygnema are generally globular and rather smaller than the zygospores, but those of Spirogyra are as a rule very similar in form to the zygospores. Klebs has stated that parthenogenetic resting-spores can be produced in filaments with long conjugating-tubes by placing them in a strong solution of sugar. Spirogyra mirabilis (Hass.) Petit is reproduced solely by spores resembling aplanospores, but produced by a degenerate form of conjugation2. Many of the upland forms of Zygnema habitually form solitary resting-cells or ' cysts ' in order to survive the winter. Sexual reproduction takes place by conjugation in all the genera of this sub-family. The usual type of conjugation is scala- riform, between the cells of two distinct filaments. The conju- gating-tube is formed exactly as in Mougeotia, and in all except species of the genus Debarya and certain species of Zygnema belonging to the section Zygogonium, the fusion of the gametes takes place in one of the gametangia. In the formation of a gamete the protoplasmic mass contracts away from the cell-wall, the chloroplast loses much of its original form, and the mass becomes of an ellipsoidal shape. The whole of this mass then glides gradually from its gametangium through the conjugating- tube into the opposite gametangium. The gametes may coalesce immediately on contact and before the one has completely passed through the conjugating- tube, or they may lie side by side in the gametangium before fusing. On the coalescence of the gametes and the fusion of their nuclei the mass generally assumes a spheri- cal or ellipsoidal form, develops a thick cell-wall and is known as the zygospore (or zygote). The cell in which the fusion of the gametes takes place and therefore the one in which the zygospore is formed, is known as the female cell, and the one which is emptied as the male cell; and that part of the conjugating-tube developed from the female 1 Nordst. 'Alg. et Char. Sandvic.' 1878, p. 17, t. 1, f. 23, 24. 2 Petit in his ' Spirogyra des envir. de Paris,' p. 14, writes concerning S. mira- bilis : "Cette tres curieuse espece ne conjugue pas et ne laisse voir aucun tube copulateur; a une certaine epoque de la vie de la plante, les cellules renflent vers le milieu, 1'endochrome se partage en deux parties qui se concentrent sous forme de globule aux deux extremites de la cellule ; il se forme ainsi une differentiation entre les parties de 1'endochronie. Bientot les deux globules se rapprochent vers la partie renflee de la cellule et fmissent par se reunir en constituent ainsi la zygospore." This is a similar phenomenon to that which occasionally occurs in the formation of the aplanospores of Gonatonema. (Consult page 118.) Zygnemacece 125 cell is usually thicker and shorter than the part developed from the male cell. The female cells frequently become much swollen after the fusion of the gametes. On the examination of a large number of conjugated examples of either Spirogyra or Zygnema one feature must impress itself even on a casual observer, namely, that "the direction of conjuga- tion is clearly governed by some physiological law, the movement of protoplasm between the two filaments almost invariably taking plnrc in one direction only, so that one of the two conjugating filaments is entirely emptied, while the other is filled with zygo- sperms1." Thus, the cells of one filament usually become all of the same sex. Two filaments are generally concerned in an example of scala- riform conjugation, but three, four, five, six, or more, are occasion- ally seen (vide fig. 49 A). Such are mostly cases of polygamy or polyandry, and statistics seem to show that the former is the more frequent. Lateral conjugation, or conjugation between adjoining cells of the same filament, is frequently observed, but it is much scarcer than scalariform conjugation and may be regarded as exceptional. It is more often met with in Spirogyra than in Zygnema and is especially frequent in some of the smaller species, such as S. tenuissima (Hass.) Ktitz., 8. inflata (Vauch.) Rabenh., and S. varians (Hass.) Kiitz. Cross-conjugation, in which some cells of the filaments are male and others female, and therefore in which perfectly normal zygospores are found in both filaments, is exceed- ingly rare. In both lateral and cross-conjugation, as was mentioned in the general remarks under the order Conjugate, a differentia- tion of sex must take place amongst the cells of the same filament, some becoming male and others female. Sometimes certain irregularities are 'met with in the conjuga- tion, and these are no doubt largely due to the increased functional activity of all the cells of the filaments which is such a striking accompaniment to conjugation. Zygospores are occasionally ob- served which have been produced by the coalescence of three gametes, two male and one female2, but attempts of this nature 1 Bennett and Murray, 'A Handbook of Cryptogamic Botany,' London, 1889, p. 266. 2 West in Notarisia 1891, vi, t. xiii, f. 13 ; Borge in Bihang till K. Sv. Vet.- Akad. Handl. Bd 17, 1891, no. 2, t. i, f. 2; W. & G. S. West in Ann. Bot. xii, 1898, t. v, f. 66. 126 Chlorophycece are usually abortive1 (fig. 49 B). Gerassimoff has observed the conjugation of two female cells with one male cell and the forma- tion of the zygospore by the coalescence of the protoplasm of the male cell with that of one of the female cells, a parthenospore being formed in the other female cell. In those plants of the ZygnemeaB in which the zygospore is formed in the conjugating- tube, conjugation between three cells entails the production of two zygospores, each of which is less than the normal size. Owing to sudden changes of local conditions it frequently happens that the conjugation has been brought to an abrupt termination before the proper formation of the zygospores has taken place. In such cases of interrupted conjugation the spores are apt to be very variable ; sometimes the spore is not of its true form, and at other times one small one is formed in each gametangium or two small ones in the female gametangium2. The discovery by Gerassimoff of binucleated cells in the Zygnemese may perhaps afford an expla- nation of some of these irrregularities of conjugation. He states that in the conjugation of binucleated cells parthenospores were sometimes observed. Rare instances of hybrids are known, in which conjugation, with the production of zygospores, has occurred between filaments of different species3. The ripe zygospores possess a thick wall of cellulose which is divisible into three coats, the outer one being cuticularized and the middle one usually exhibiting some form of sculptured mark- ings. The contents of the zygospore often turn red in colour and develop a large amount of oily material. Sometimes the chloro- plasts of the two gametes remain intact in the zygospore ; some- times those of the female remain intact and those of the male disintegrate ; but it is quite a common thing for the chloroplasts to completely disintegrate before the fusion of the gametes. The zygospores undergo a period of rest, surviving the winter or even a period of drought, and they usually germinate after the conju- 1 W. & G. S. West, 1. c. figs. 67 and 69 ; Schmula in Hedwigia, xxxviii, 1899. (c. fig.) Copeland states that in such a case the nucleus of the abortive male cell is situated against the wall opposite, remote from the conjugating-tube. (Cf. Bull. Torr. Bot. Club, xxix, 1902.) 2 Rosenvinge in Ofvers. K. Vet.-Akad. Forh. 1883, no. 8, t. viii, f. 1—11; West in Notarisia 1891, vi, t. xiii, f. 27, 28; Hansgirg in Hedwigia 1888, t. x, f. 6; W. & G. S. West, 1. c. t. v, f. 74—80. 3 Cf. Spirogyra maxima var. iruequalis Wolle Freshw. Alg. u. s. t. cxxxviii, f. 5, 6; t. cxlii, f. 5, 6; W. & G. S. West, 1. c. t. v, f. 70, 71. Zygnemacece 127 gating filaments have entirely perished. In Spirogyra the two outer coats are ruptured, generally at one end of the spore, and the protoplasm is protruded as a filament clothed with the inner- most cellulose wall. This filament becomes divided by a transverse septum, one cell becoming an organ of attachment and containing little or no chlorophyll, whereas the other cell increases in size, contains one or more chloroplasts, and by repeated divisions forms a filament. The distinction between base and apex is soon lost and the filament floats freely in the water. Organs of attachment have, however, been observed to be developed subsequently from older cells. In the germination of zygospores of Zygnema the distinction into base and apex is scarcely evident. Certain of the zygospores of Spirogyra velata Nordst. have been observed to germinate immediately after their formation without the development of a thick cell- wall (fig. 49 E and F)1. Genus Debarya Wittr., 1872. [Mougeotiopsis Palla 1894.] The thallus consists of simple, cylindrical filaments, with or without a distinct constriction between the cells, and with a thin external mucous covering. There is one chloroplast in each cell, disposed as an axile plate similar to that of Mougeotia, and containing several pyrenoids. In rare instances pyrenoids are absent. The gametes are formed from the entire contents of the gametangium and conjugation takes place in the conjugating- tube, the mature zygospore occupying a position between the gametangia. The zygospores are veiy variable in character and there are consider- able differences in the actual processes of conjugation, but in one curious fact all the species agree. A peculiar change comes over the empty gametangia as the zygospore is being formed; they become very clear and refractive, and sometimes a series of stria- tions become visible parallel to the transverse walls. They have at this stage the appearance of solidity, most likely owing to the deposition of annular thickenings of cellulose inside the cell-wall on the receding of the protoplasm during conjugation. This feature is noticeable not only in living specimens, but also in old, preserved examples. All the species of this genus are of rare occurrence. D. glyptosperma (De Bary) Wittr. is more widely distributed than the others; the cells are 9— lf>yu in thickness and 6 — 15 times longer than the diameter; the conjugati tig-tubes 1 W. & G. S. West in Ann. Bot. xii, 1898, t. v, f. 84, 85. 128 are often very long and the zygospore is large and ellipsoidal, frequently with one or two mamillate protuberances at the poles ; length of zygosp. 35 — 72 /x, breadth 16—40 /* (fig. 46 A). D. Icevis (Kiitz.) W. & G. S. West is a larger species with shorter cells, which are 20 — 26 p in thickness and 2| — 4 times Fig. 46. A, Debarya glyptosperma (De Bary) Wittr., from Fairfield, Westmoreland (x275). B, D. calospora (Palla) W. & G. S. West, from Pilmoor, N. Yorks. ( x430). C— E, D. leevis (Kiitz.) W. & G. S. West, from Mitcham Common, Surrey; C, x!80; D, x250; E, mature zygospore, x 430. F— I, D. Desmidi- oides W. & G. S. West, from near the Lizard, Cornwall ( x 430). longer than the diameter. The zypospore is ellipsoidal (44 — 50 p. x 29 — 36 fi) with a scrobiculate middle coat (fig. 46 C — E). D. calospora (Palla) W. & G. S. West is 11 — 13 /x in diameter; the zygospores are subglobose or ellip- soidal, 18 — 26 fj. in diameter, and ornamented with large scrobiculations Zygnernacece 129 (fig. 46 B). Palla1 placed this species under a new genus of the Conjugate owing to the absence of pyrenoids in the plants he observed. More recently, however, precisely the same species has been discovered with pyrenoids, and as the latter are subject to much variability their presence or absence is of no generic value2. The most remarkable species of the genus is D. Desmidwides W. & G. S. West3, which, up to the present time, has only been observed from Cornwall. The cells are short, only 2^ — 6^ times longer than the diameter and 7 '1 — 8'6 \t in thickness (fig. 46 F — I). There is a most evident constriction between all the cells of the filaments, and the latter dissociate with the greatest ease into their individual cells, conjugation only occurring between the free, dissociated cells. This plant throws much light on the origin of the Desmidiacese. Genus Zygnema Ag., 1824. [Zygogonium Ktitz. 1843.] The filaments are simple, consisting of a single series of cylindrical cells placed end to end, and sometimes exhibiting a slight con- striction at the points of junction. Each filament possesses an external mucous coat which is sometimes remarkable for its size and strength. There are two star-shaped chloroplasts suspended in the median line of each cell, each one containing a single large pyrenoid. Sometimes the chloroplasts are very indefinite, their form and disposition being difficult to make out. This is particularly the case in Z. ericetorum (Kiitz.) Hansg., some forms of which greatly resemble species of Microspora or of Rhizoclonium. The coalescence of the gametes takes place either in one of the gametangia (the female) or in the conjugating-tube. Species in which the latter occurs were referred by Kiitzing to a separate genus — Zygogonium. The zygospores are globose or ellipsoid. There are about a dozen British species of this genus, of which Z. ericetorum (Kiitz.) Hansg. (fig. 47 C) is the most widely distributed. This species lives equally well in water or on damp heaths or peaty moors, and it frequently assumes a purple or violet colour owing to the formation of phycoporphyrin in the cell-sap. It is an Alga which fulfils an important function on some of the heaths and moors. In the drier and hotter periods of the year, thickly- matted sheets of Z. ericetorum, often many square feet in extent, are found covering wide patches of almost bare sand or peat, round such plants as Drosera, Carices, etc. These mats of Zygnema have great absorptive capacity, greedily taking up water, and in this way they regulate the moisture of the surface soil, the thriving of some of the smaller Phanerogams depending to a 1 E. Palla, ' Ueber erne neue, pyrenoidlose Art und Gattung der Conjugaten,' Berichte Deutsch. Bot. Gesellsch. xii, 1894, Heft 8, pp. 228—236, t. xviii. 2 W. & G. S. West in Ann. Bot. xii, 1898, p. 49; in Journ. Bot. Aug. 1900, p. 289. 3 W. & G. S. West in Journ. Bot. 1903, p. 7 (Sep.), t. 446, f. 1—9. W. A. 9 130 Chlorophycece great extent on the presence of the Zygnema1. Z. ericetorum very rarely con- jugates, and mature zygospores, which are found in the conjugating- tube, have only been observed on one or two occasions. The filaments are 15 — 22 p. in diameter and the cells often become irregularly thickened. Fig. 47. A, Zygnema stellinum (Vauch.) Ag., from Cam Fell, W. Yorks. (x430). B, Z. Vaucherii Ag. var. stagnate (Hass.) Kirchn., from near the Lizard, Cornwall ( x 430). C, Z. ericetorum (Kiitz.) Hansg., from Bombald's Moor, W. Yorks. ( x 415). I), Z. leiospermum De Bary, from Esher Common, Surrey ( x 430), a portion of a filament which was conjugating along the greater part of its length. E, Z. insigne (Hass.) Kiitz., from Malham, W. Yorks. (x330). F, Z. Ealfsii (Hass.) De Bary, from Chippenham Fen, Cambridgeshire ( x 430). ap, aplanospore. 1 This phenomenon is much more evident in some parts of the tropics, and attention was first called to it by Welwitsch in the ' Journal of Travel and Natural History,' vol. i, 1868. In the damp sandy valley of the Cuanza River, in Angola, the Alga Porphyrosiphon Notarisii occurs in extensive sheets, closely spread like a Zygnemaeece 131 Z. pectinalum (Vauch.) Ag., Z. cruciatum (Vauch.) Ag. and Z. insigne (Hass.) Kiitz. (fig. 47 E) are the three largest British species, usually occurring in ponds or in road-side ditches. The smallest form of the genus is Z. Vauch- erii Ag. var. stagnate (Hass.) Kirchn. (fig. 47 B), the filaments of which reach a maximum thickness of 13 /x. Z. anomalum (Hass.) Cooke is a species largely confined to upland bogs and is remarkable for its wide mucous in- vestment. Genus Spirogyra Link, 1820. This is the best known and most abundant genus of Conjugate, and it has a distinct preference for low-lying, quiet waters, such as those of ponds and ditches. The fila- ments are quite simple and occur in bright green flocculent masses, often several feet in diameter. The cells are cylindrical and they exhibit great variability both with re- gard to their diameter and their relative length. The cell- wall is firm, with an outer mucous coat which renders the plants very slimy. In most species the transverse cell-walls are quite plane, but in some of the smaller species there is a curious annular ingrowth of cel- lulose at the ends of each cell (vide fig. 48 C). When this is present the cells are Fig. 48. A, Spirogyra majuscula Kiitz., from Coates, Gloucestershire, single cell showing chloro- plasts and nucleus (x 300). B, Spirogyra sp., from Coates, Gloucestershire ( x 370). C, S. tenuis- sima (Hass. )Kutz., from Mitcham Common, Surrey ( x 390). n, nucleus. said to possess " replicate ends." It is a character which is constant for the species in which it is found, although the ingrowths are not net over the soil, intergrown with small herbaceous plants and shrubs. The mat- like sheets of the Alga eagerly absorb the atmospheric moisture during dewy nights, affording by this means a refreshing protection to the roots of many other and larger plants during the glowing heat of the following day. Welwitsch states that the growth and thriving of the numerous small phanerogamous plants in these places is conditional on the co-presence of the Alga. Cfr W. & G. S. West in Journ. Bot. 1897, p. 303. 9—2 132 Chlorophycece necessarily present at the extremities of every cell in the filament. The nucleus is situated in the central portion of the cell and the protoplasm in which it is embedded is connected with the lining primordial utricle by numerous delicate strands. Many of these strands reach the lining protoplasm exactly opposite a pyrenoid, and as the starch formed during carbon-assimilation makes its appearance round the pyrenoids, this fact has been brought forward as a reason for supposing the nucleus to have a direct function in starch-formation. The nucleus is often clearly visible in living specimens, particularly of 8. majuscula Kiitz. and S. pellucida (Hass.) Ktitz. Mitotic division has been observed in this nucleus by Mitzkewitsch and by C. van Wisselingh, and Gerassimoff has observed cells with either a compound nucleus or two ordinary nuclei. The chloroplasts are the most striking feature of Algae belonging to this genus. They are disposed in the primordial utricle in the form of spiral bands, and they vary in number from one to about six or seven in each cell. In some species they are coiled into very close spirals, but in others they are practically straight and longitudinal ; in some, as in S. neglecta (Hass.) Kiitz., their margins are quite smooth and there is a regular axile series of pyrenoids ; in others, as in 8. nitida (Dillw.) Link or 8. porticalis (Vauch.) Cleve, the spiral bands are very broad, with serrated margins and scattered pyrenoids. Between these two extremes there is every gradation, and the character of the chloroplasts always remains constant for any particular species, even though the number of them may vary in different cells of the same filament. It has been ascertained by Kolkwitz1 that the chloroplasts grow in length in the direction of the coils by both apical and intercalary growth ; and therefore, as this is obliquely to the surface of the cell-wall, there is a gliding motion of the spiral bands through the primordial utricle. The coalescence of the gametes takes place in all cases in the female gametangium, which often swells up to twice its normal size. The zygospores may be globular, ellipsoidal, cylindrical with obtuse ends, or they may more rarely assume the form of flattened discs ; and the middle coat of the zygospore is frequently ornamented with distinctive markings. 1 Kolkwitz in Festschr. f. Swendener, 1899, pp. 271—287. Zygiiemacece 133 Fig. 49. A, Spirogyra nitida (Dillw.) Link, from near Morecambe, Lancashire; scala- riform conjugation between six filaments ( x 75). B, S. setiformis (Both) Kiitz., showing frustrated attempts at the conjugation of two male cells and one female cell ( x 90). C, S. Spreeiana Rabenh., from near Esher, Surrey ( x 390). D, S. inftata (Vauch.) Rabenh., from near Esher, Surrey; showing lateral conjugation ( x 390). E and F, zygospores of S. velata Nordst., from Shipley Glen, W. Yorks., germinating immediately after their formation and before the differentiation of the wall of the zygospore ( x 165). G, germination of zygo- spore of S. velata after normal period of rest ( x 230). 134 There are about 24 British species of the genus, S. gracilis (Hass.) Kiitz. being the smallest, with a minimum thickness of about 10 p., and S. crassa Kiitz. the largest, with a maximum thickness of about 150 p.. Several species, such as S. tenuissima (Hass.) Kiitz. (fig. 48 C), S. gracilis (Hass.j Kiitz., S. communis (Hass.) Kiitz., S. varians (Hass.) Kiitz. and S. nitida (Dillw.) Link (fig. 49 A), are abundant in every part of the British Islands except in the most mountainous districts. S. velata Nordst. and S. calospora Cleve are notable for their beautifully marked zygospores. Plants of this genus often cause trouble in cress-beds, the matted masses of Spirogyra preventing the growth of the cress plants. Genus Choaspis S. F. Gray, 1821. [Sirogonium Kiitz., 1843.]' It is very doubtful if this genus should be separated from Spirogyra. The filaments are similar to those of many species of the latter genus and the chloroplasts, although more or less straight and longitudinal, are not jjll straighter than those of ^^ 1 111 / % Spirogyra majuscula or ^i A P L--1 f~\ S. pellucida. There are, • I \ /jj^^ however, certain constant W distinctions. There is a /^ great diversity of form and their wonderful symmetry. Indeed, the group includes some of the most beautiful of microscopic objects. They are unicellular plants and the major portion of them lead a solitary existence. Certain of them are, however, associated in colonies and others are more or less closely united into long filaments. They are essentially free-floating Algae and frequently occur in enormous abundance in small ponds, in the quiet margins of lakes, and in other favourable localities. Most Desmids exhibit a more or less distinct constriction into two perfectly symmetrical halves; each half is termed a semicell and the narrower part connecting the two semicells is known as the isthmus. The angle resulting on either side from the con- striction or narrowing of the cell is known as the sinus. One of the most striking features of the family is the extra- ordinary complexity of the cell-outlines. The cell is often deeply lobed or incised, and the exterior of the cell-wall is frequently covered with granules, spines, wart-like thickenings, or other pro- tuberances, most of which have a definite pattern of arrangement. This firmer portion of the cell-wall consists chiefly of cellulose, and external to it are layers of gelatinous pectose compounds. The latter often form a thick mucilaginous coat completely surrounding the individual, or, as in the case of colonial forms, entirely envelop- ing the colony. It is by means of this mucilaginous envelope that Desmids adhere to other larger aquatic plants, and sometimes, when the conditions have been favourable for rapid multiplication, enormous numbers of individuals occur embedded in masses of jelly. Sometimes the mucus is very tough. In the genus Spon- 1 S. F. Gray, Arrang. Brit. Plants, 1821, vol. i, p. 299. 136 Chlorophycece dylosium the cells are united into filaments by mucous threads passing between their apposed ends, and the filaments break much more readily across the isthmus of a cell than at the points of apical attachment. The minute structure of the cell-wall was first studied by Klebs1 who examined the nature of the gelatinous outer coat and also demonstrated the presence of pores in the cell-wall. Shortly afterwards Liitkemiiller2 described the pores in the cell-wall of Closterittm and quite recently he has published a very important account of the structure of the cell-wall of Desmids3. In a few Desmids — those belonging to the Spirotseniese— the cell-wall consists of a single layer of cellulose of homogeneous structure, but in the majority of Desmids it is composed of two well differentiated layers. The inner layer is structureless and consists of cellulose ; the outer layer is stronger and thicker, con- sisting of a ground substance of cellulose through which pass numerous tube-like structures or 'pore-organs.' The latter are not composed of cellulose, and a small pore or canal runs through the middle of each one. The contents of these canals also traverse the inner layer of the cell-wall and often terminate on its inner surface in lens-shaped or bulbous swellings. From the outer end of the pore-organs there often arises a delicate flower-like or club- shaped structure through which the canal passes. More often this structure is entirely wanting or is replaced by a small perforated button or rod. In many of the larger Desmids there are numerous, smaller, thread-like pores between the larger canals and only traversing the outer layer of the cell-wall. Outside the differen- tiated parts of the cell-wall is the mass of gelatinous pectose compounds present in so many species, and which is secreted by the protoplasm and passed outwards through the pores. This outer gelatinous coat often exhibits a prismatic or fibrillar struc- ture and is frequently the home of epiphytes or of numerous rod- shaped bacteria. The cell-wall sometimes contains a trace of silica. With the exception of the lining primordial utricle the 1 Klebs, 'Ueber Bewegung und Schleimbildung der Desmidiaceen,' Biol. Centralbl. Bd v, 1885. 2 Liitkemiiller, 'Die Poren der Desmidiaceen Gatt. Closterium Nitzsch,' Oesteir. botan. Zeitschr. Bd 44, 1894. 3 Liitkemiiller, 'Die Zellmembran der Desmidiaceen,' Beitrage zur Biol. der Pflanzen, herausgegeberi von F. Cohn, Bd viii, Breslau, 1902. Desmidiacece 137 cytoplasm is variable in its general disposition, the variability depending largely on the nature and arrangement of the chloro- plasts. In those Desmids with larga, central chloroplasts, vacuoles may be absent or much reduced, and they are often confined to one at each extremity of the cell ; in others with parietal chloro- plasts large vacuoles are often present in the central portions of the cell. The general transparency of the cell-wall enables the circula- tion of the protoplasm to be seen extremely well, especially in the larger species. The nucleus is usually embedded in a small mass of protoplasm in the median part of the cell in the region of the isthmus, and in some genera is readily visible without the use of reagents. In the genera Gonatozygon, Closterium and Pleuro- tcenium, and in certain species of the genus Penium, there is a well marked terminal vacuole at each extremity of the cell, con- taining one or many moving granules. These granules, which may be quite irregular in form or of some definite shape, exhibit rapid vibratory movements and have in the genus Closterium been shown to be minute crystals of gypsum. Their movements cease immediately on tKr " V Penium \ -IV 'C^JPenium LiboTluhf^V" ^ — x. / S I * Roya > Tetmemorus -y I / ± Closterium .' CLOSTERIE^E Docidium Pleurotsenium \ Cosmarium Micrasterias Xanthidium Staurastrum y ..••" 'SpondyL \ • / Hyalotheca \ '. ^ Arthrodesmus \ COSMARIEJS Onychonema "•. Sphaerozosma _./ \ '•, Phymatodoois -• Li;'lll . _ . j \ .**' Streptonema . x .^ 4: ^ . Desmidium / x^ ./ (Didymopriutn) ^"^ ' 1 ' -. / ft 'f / <. __ Gymnozyga ^, Phylogeny of the Genera of Desmids. There is little question that this complexity of outline, which is so frequently accompanied by a defensive armour of spines and spinous processes, has been acquired as a means of defence against the Desmidiacece 145 attacks of small aquatic animals. After the loss of the filamentous condition it became necessary for the solitary and unprotected individuals to acquire some other means of defence, and presumably the present morphological complexity is the result. It is a notable fact that those species which occur on wet rocks and in other localities in which Amoebae, Oligochsetes, Tardigrades, Crustacea, etc., are either absent or very scanty, especially at high elevations, usually possess a comparatively simple outline and are provided with a more or less abundant mucus; whereas those species oc- curring in deep bog-pools, in the plankton, and the quiet margins of deep lakes, in which localities such enemies abound, are generally possessed of a more complicated, and in many cases of a formidable, exterior. These characters acquired by the unicell are not only protective against the depredations of aquatic animals, but are also useful as anchors in the time of floods, and in their acquirement the Law of Symmetry has exercised its full influence, with the result that exquisite patterns have been produced which exhibit a symmetry far ahead of that shown by any other living vegetable organisms. There are several thousand known species of Desmids, about one quarter of which are British, and almost all of them can be readily identified by their external morphological features. Some are cylindrical with rounded or attenuated apices ; many of them are flattened and often disciform ; and others are of a radiating character- To one who is not sufficiently versed in solid geometry there are few greater surprises than the extraordinary aspects presented by some of these plants. The majority of Desmids have three principal axes of symmetry at right angles to one another, and for this reason they require examining in three positions. The most important aspect is the front view, in which the plant is observed in that plane containing the two longest axes. The other important aspects are the vertical view and the side (or lateral} view (vide fig. 51 E and F). Desmids are subject to considerable variation, but only within certain limits, and one of the most extraordinary facts relating to these plants is the constancy of the markings embellishing the exterior of the cell-wall. The following is a summary of the present state of our knowledge concerning the variation of Desmids1: — 1 G. S. West, ' On Variation in the Desmidieae and its Bearing on their Classifi- cation,' Journ. Linn. Soc. Bot. xxxiv. 1899, p. 376. W. A. 10 146 Chlorophycece (1) The structure of the cell-contents is one of the most constant features exhibited by a species; but this fact can be of little classificatory value owing to the very large number of species which possess the same structure and arrangement of the chro- matophores. (2) The outward form of the cell, as seen in front view, varies within certain limits, which are usually very small, but which may in exceptional cases (such as in pure cultures) be considerable. The form of the vertical view is, as a rule, a more constant feature than the form of the front view. (3) The ornamentation (scrobiculations, granulations, spinu- lations, etc.) of the cell- wall is relatively constant, being always arranged according to a definite law, which is only transgressed by variations in one or more of the individual component groups which constitute the pattern of arrangement. (4) The prolific growth and rapid division of immense numbers of Desmids have a tendency to produce variations from the typical forms. (5) Changes in the conditions of environment cannot affect the characters of a species unless they act for long periods of time. It is most unfortunate that so little is known concerning the geographical distribution of Desmids, as such a knowledge would probably be of much greater value than one would at first sight imagine. I have previously shown that the production of per- manent variation in species of Desmids under natural conditions is much more difficult than is generally supposed1; also, that some of the prettily marked species are found in such widely separated localities as Ceylon, Java, Hong Kong and Queensland, identical in every respect and possessing precisely the same markings2. It is likewise most improbable that this result has been brought aboii t by a parallelism of modification in the course of the evolution of these forms, owing to the occurrence of other species with a world-wide distribution and equally constant characters. The distribution of Micrasterias foliacea Bail, is sufficient to settle this point, as the plant in question is the most aberrant of all forms of the genus Micrasterias, having secondarily assumed a filamentous condition ; and yet the plants found in North and South America, India, Burmah, Siam, China, Australia and New Zealand cannot be distinguished from one another. It" should also be borne in 1 G. S. West, 1. c. p. 371. - W. & G. S. West in Trans. Linn. Soc. Bot. ser. 2, vol. vi, 1902, p. 124. Desmidiacece 147 mind that the transference by natural means of living specimens of any Desmid from some of these countries to any of the others is an utter impossibility, desiccation, or in many cases even partial drying, being quickly followed by death, and submergence in sea-water is equally fatal1. Moreover, zygospores, which might possibly withstand the entailed vicissitudes if circumstances arose by which they could be transferred from one country to the other (such as by the long flight of a wading-bird), are so rarely found that distribution by their means across an expanse of ocean is almost impossible. There is but one conclusion to be arrived at from a consideration of these facts, namely, that such a species has been, perpetuated by isolated communities which were derived originally from a common stock, and that the individuals of these communities have retained their original characters in an extra- ordinarily constant manner. Thus, it seems probable that a sound knowledge of the distribution of Desmids would shed much light on the subject of previous land-connections, and might perhaps afford more reliable evidence on this point than that afforded by the known distribution of any other plants or animals. As a significant instance, it may be mentioned that several remarkably fine Desmids, such as Staurastrum Ophiura Lund., St. Arctiscon (Ehrenb.) Lund., St. jaculiferum West, St. longispinum (Bail.) Arch., St. Cerastes Lund., St. Brasiliense Nordst. var. Lundellii W. & G. S. West, Micrasterias furcata Ag., M. conferta Lund., Pleurotanium nodosum (Bail.) Lund., and others, are not uncommon in the eastern parts of N. America and that in Europe they are only abundant on the north-western shore districts of Ireland, Wales, Scotland, the Outer Hebrides, Scandinavia and Lapland. One of these species — Staurastrum jaculiferum West — is also known from the Shetland Is., the Faeroe Is. and Iceland. Borge has examined a number of subfossil Desmids from the glacial clays of the Isle of Gotland, and a few subfossil forms of existing species have also been noted from an ancient peat deposit near Filey in E. Yorkshire. Desmids thrive best in soft water, and they are most numerous in peaty water which has a trace of acidity. With few exceptions they do not flourish in water containing carbonate of lime in solution, and no good collection of Desmids can be made in a purely limestone district in which the water is hard. 1 One Desmid has been described as inhabiting brackish water, viz. : Cosmarium salinum Hansg. in Oesterr. hot. Zeitschr. 1886, p. 335. 10—2 148 Chlorophycece I have attempted to give a reasonable classification of the genera of Desmids based upon the evolutionary scheme previously mentioned1 and upon the recent and sound observations of Lutkemiiller2. It is very interesting to note that Liitkemuller's conclusions, which he arrived at chiefly from the study of the minute structure of the cell-wall, coincide almost entirely with the scheme I put forward in 1899, which was based upon a compre- hensive study of the external morphological features of these plants. The division of Desmids into filamentous forms and solitary forms, such as is adopted by many writers even at the present time, is no longer tenable ; and such an arrangement as that given by Bessey3, in which he places Desmids under the three tribes 'Desmidieae,' 'Arthrodieae' and 'Cosmarieaa,' is obviously one which is not based upon a careful study of the Desmids themselves and is therefore of no value. Most Desmids would appear to have had an origin from the genera Mesotcenium and Cylindrocystis, which were themselves derived by retrogression from ancestral filamentous Conjugates4. The genera Gonatozygon and Genicularia have so little in common with most other Desmids, and resemble so much some of the present existing filamentous Conjugates, that they must be re- garded as having had a distinct origin from filamentous ancestors. They are however, more specialized than the genera Spirotcenia, Mesotcenium or Cylindrocystis. The genus Penium is the most difficult to relegate to its proper place. In the sense in which this genus is generally regarded it undoubtedly contains many widely different plants, and therefore one hails with delight Lutkemiiller's suggestion that the name Netrium be again brought forward as a distinct genus to include four species which obviously form a natural group. On the removal of these four plants from the genus, the remainder do not fit satisfactorily into any one place in the scheme of classification, and the difficulty lies in the fact that our knowledge of the plants 1 G. S. West in Journ. Linn. Soc. Bot. xxxiv, 1899. 2 Lutkemuller in Beitrage zur Biol. derPflanzen, herausgegeben von Dr F. Cohn, Bd viii, Breslau, 1902. 3 Bessey in Trans. Amer. Micr. Soc. xxii, 1(J01. 4 Had these genera originated directly from Flagellate forms, it is scarcely conceivable that the motile condition would not be frequently reverted to ; in fact, it is reasonable to suppose that it would play a considerable part in the life-history of these Algae. Such is the case in all groups of Algce with a direct Flagellate ancestry ; and the entire absence of motile forms of any description from the Desmidiacese lends strong support to the view put forward from other considera- tions, of the origin of this family of unicells by retrogression. Desmidiacece 149 is too scanty to allow of splitting them up into a number of separate genera. One cannot see how, in the present state of our know- ledge, such genera could be defined, and yet some of these plants are certainly not nearly related. The plant commonly known as Penium minutum (Ralfs) Cleve is the most puzzling of all. I have accepted the two sub-families proposed by Liitkemuller and also his five tribes, but have placed the " Gonatozyga3 " first and altered the definition of the " Peniese " in order to include the heterogynous collection of Desmids embraced in the present genus Penium. The following is a synopsis of all the known genera of Desmids, four of which (Ichthyocercus, Triploceras, Phymatodocis and Strep- tonema) are exclusively tropical and one (Ancylonema) is exclusively arctic. Sub-family I. SACCODERM.E. Cell-wall unsegmented and without pores. Point of division of cells indefinite and unknown previous to the actual division. The young half of the cell is developed obliquely and its walls are absolutely continuous with the walls of the older hah0. Tribe 1. G-onatozygse. Cells elongate, cylindrical and unconstricted, forming loose filaments. Cell- wall with a differentiated outer layer of which the small roughnesses and spines form a part. * Chloroplasts axile 1. Gonatozygon. ** Chloroplasts parietal and spirally twisted ... 2. Genicularia. Tribe 2. Spirotaenieae. Cells solitary, relatively short and mostly un- constricted. Cell-wall a simple sac, without a differentiated outer layer. The cell becomes adult by periodical growth. * One chloroplast in each cell. t Chloroplast spirally twisted, axile or parietal 3. Spirotcenia. tt Chloroplast plane, axile. § Cells solitary 4. Mesotcenium. §§ Cells forming short filaments 5. Ancylonema. ** Two chloroplasts in each cell. t Chloroplasts star-shaped, radiating from a central pyrenoid 6. Cylindrocystis. tt Chloroplasts ridged with longitudinal serrated ridges 7. Netrium. Sub-family II. PLACODERM.E. Cell- wall segmented, with a differentiated outer layer. Cell-division follows a fixed type, with the interpolation of the younger halves between the old ones. The younger portions of the cell-wall are joined to the older portions by an oblique surface. 150 Chlorophycew A. Point of division of cells variable or sometimes fixed (at the isthmus). Tribe 3. Peniese. Cells of moderate length, straight, cylindrical, some- times with a slight median constriction. Cell-wall with or without pores. Point of division of cells often variable. The cell often arrives at maturity by periodical growth. 8. Penium. Tribe 4. Closterieae. Cells elongate, generally curved ; symmetrical in one longitudinal plane only. . Cell-wall commonly with pores. Points of division regularly placed in the middle region of the cell. * Cells almost cylindrical, scarcely attenuated. Chloroplast single, without apical moving grannies 9. Roya. ** Cells strongly attenuated towards each ex- tremity. Two chloroplasts in each cell, with apical moving granules 10. Closterium. B. Point of division of cells always fixed (at the isthmus). Tribe 5. Cosmarieae. Cells exhibit great variety of form, and the cell- wall consists of two thin, firm layers with pores. There is no periodical growth, the cell becoming adult immediately after division by the mature growth of the young semicell. a. The point of division of the cell, where the new and old parts of the cell-wall are obliquely fitted together, remains plane during division. Solitary or colonial. * After division the cells remain free and solitary. f Cells elongated and cylindrical ; constriction slight. § Apices of cells truncate or rounded. \ Base of semicells plicate 11. Docidium. 1 I Base of semicells plane 12. Pleurotcenium. §§ Apices of cells cleft, incision open or narrow. I Cell-wall adorned with rings of furcate processes 13. Triploceras. II Cell-wall plane. © Apical incision widely open, each apical angle furnished with a spine 14. Ichthyocercus. ©0 Apical incision narrow ... 15. Tetmemorus. tt Cells relatively short, commonly compressed or radiating, con- striction usually deep. § Cells compressed (at right angles to the plane of the front view) ; from the vertical view fusiform or elliptical. I Cells generally with an apical in- cision and a central protuber- ance, moderately lobed 16. Euastrum. I I Cells very compressed and deeply lobed or incised 17. Micrastenas. HI Cells with a more or less entire margin, often fur- nished with warts or spines. Desmidiacew 151 © Cells commonly with a central protuberance. IT Cell-wall smooth, granu- late, verrucose, etc. Central protuberance present or absent 18. Cosmarium. ITT Cell- wall with regularly arranged spines, com- monly in pairs. Cen- tral protuberance al- ways present 19. Xanthidium. ©© Cells without a central pro- tuberance; angles spinate 20. Arthrodesimis. §§ Cells from the vertical view com- monly radiating, triangular, quad- rangular, or up to 11 -radiate, rarely fusiform 21. Staurastrum. ** After division the cells remain attached to form colonies. t Colonies spheroidal ; cells not in contact, but joined by gelatinous bands. § Gelatinous bands narrow; few cells forming a microscopic colony 22. Cosmocladium. §§ Gelatinous bands very broad; many cells forming a macroscopic colony 23. Oocardium. ft Colonies thread-like; cells attached by their apices to form long filaments. § Cells attached by special apical processes. \ Apical processes very short 24. Sphcerozosma. 1J Apical processes long and over- lapping the apices of the ad- joining cells 25. Onychonema. §§ Apices of cells plane and flat. J Cells deeply constricted. © Cells in vertical view elliptical 26. Spondylosium. © © Cells in vertical view quad- rangular with produced angles 27. Phymatodocis. \\ Cells very slightly constricted... 28. Hyalotheca. b. The point of division of the cell, where the new and old parts of the cell-wall are obliquely fitted together, develops a girdle-like thickening or ingrowth, which projects both ways into each of the old semicells during division. Cells attached to form thread-like colonies. * Cells joined by special apical processes 29. Streptonema. ** Cells joined by their flat apices or by flattened apical projections, t Cells short, in vertical view fusiform, trian- gular or quadrangular (rarely circular with produced angles) 30. Desmidium. tt Cells elongate, cylindrical 31. Gymnozyga. 152 Chlorophycece Sub-family I. SACCODERM^E. This is a very natural group of Desmids in which the cell-wall is unsegmented and destitute of pores. There is no line of de- marcation between the newer semicell and the older semicell, the cell- wall being absolutely continuous. Division takes place at no fixed part of the cell (except in a few species of Cylindrocystis)a,nd the young semicells are developed obliquely, gradually sliding away from one another as they reach maturity. Tribe 1. Gonatozygce. This tribe only includes two genera which are considerably removed from other Desmids. The cells are long and cylindri- cal, and are joined by their apices into fragile filaments of variable length. The filaments easily break up, but this in no way inter- feres with the life of the individual cells. Conjugation only takes place between cells which have become free. The cell- wall is layer being hyaline and Fig. 53. A and B, Gonatozygon Brebissonii De Bary (x464); A, from Esher Common, Surrey; B, from Strensall, N. Yorks. C— E, G. Brebissonii var. lave (Hilse) W. & G. S. West, from Mickle Fell, N. Yorks. (x356). F and G, G. Brebissonii var. minutum W. & G. S. West, from Eiccall Common, E. Yorks. ( x 464). H, zygospore of G. monottenium De Bary ( x 464). I and J, Genicularia Spirot o> ^^ B Fig. 96. Kirchneriella obesa (West) Schmidle. A, B, D and E, from Bowness, Westmoreland ; C, from the plankton of Loch Mor Bharabhais, Lewis, Outer Hebrides ( x 485). K. obesa (West) Schmidle (breadth of cells 2 — 9 '5 p ; apices 1'5 — 4 p. apart ; greatest diameter of cell 6 — 16 /a; fig. 96 A — E) and K. lunaris (Kirchn.) Mob. are widely distributed in the British Islands, occurring sparingly in the small ponds and lakes, but in quantity in the plankton of the larger lakes. Sub-family IV. OOCYSTIDE^. This sub-family is characterized by the globose or ellipsoid cells (curved or even sublunate in Nephrocytium), which are frequently retained within the swollen wall of the old mother-cell. There may be one or many chloroplasts in each cell, which are parietal and usually contain one pyrenoid. In all except Palmellococcus the cell-walls are firm and somewhat thick. The multiplication is by autospores, which generally grow and attain their full size whilst still forming part of the mother-colony. The following are the British genera : — * Cells ellipsoid Oocystis. ** Cells curved, subcylindrical or sublunate Nephrocytium. *** Cells spherical. t Cells large, solitary and free-floating Eremosphcera. v tt Cells minute, forming a thin stratum Palmellococcus. ttt Cells minute, sparsely scattered and symbiotic Chlorella. Protococcacece 227 Genus Oocystis Nag., 1845. The cells are ellipsoid, sub- cylindrical or panduriform, with a firm cell-wall which commonly possesses a nodular thickening at each pole. There are usually several parietal chloroplasts in each cell, destitute of pyrenoids. In some cases, however, there may be one pyrenoid in each chloroplast. Multiplication is by autospores, which are generally retained for some time within the greatly swollen wall of the mother-cell. Sometimes several generations are contained within one large mother-cell-wall. Fig. 97. A and B, Oocystis solitaria Wittr., from Ben Lawers, Perthshire. C and D, 0. crassa Wittr.; C, from Lanlivery Moor, Cornwall; D, plankton form from Lough Beg, Ireland. E and F, 0. panduriformis W. & G. S. West; E, from Pilmoor, N. Yorks. ; F, from near Clifden, Ireland. G, 0. elliptica West, from Derryclare Lough, Gal way, Ireland. (All x 485.) There are about ten British species of the genus, some of which are widely distributed in the quiet waters of ponds and lakes. 0. solitaria Wittr. (length of cells 15— 48 p.; breadth 9'5— 25 p.; fig. 97 A and B) is undoubtedly the commonest species, although 0. elliptica West (fig. 97 G) is abundant. 0. parva West & G. S. West (length 6 — 12 p. ; breadth 4 — 7 p.) is the smallest species and 0. gigas Arch, (length 41 — 5O5 p. ; breadth 32'5 — 40 p.) is the largest. 0. crassa Wittr. is not common except in the plankton; fig. 97 C and D. 0. asymmetrica W: & G. S. West is another solitary species. Chodat states that 0. gigas Arch, and 0. panduriformis W. & G. S. West (fig. 97 E and F) are merely stages in the life-history of Eremosphcera, but this statement I do not accept. These plants often occur in localities from which Eremosphcera is absent and they reproduce themselves in the manner of true species of Oocystis. Moreover, I invariably find the life-history of Eremosphcera to be remarkably free from polymorphic forms (vide page 229). 15—2 228 Chloi'ophycece Genus Nephrocytium Nag., 1849. The cells are oblong, ellipsoid or subcylindrical, slightly curved or sublunate, sometimes almost reniform. There is at first a large expanded chloroplast in each cell, furnished with a single pyrenoid, but later the chloroplast fragments. The multiplication is by autospores similar to those of Oocystis, and formed within the mother-cell soon after the segmentation of the chloroplast. The young autospores are often spirally disposed round the inside of the mother-cell-wall. The genus is distinguished from Oocystis primarily by its curved cells without any trace of apical thickenings. m Fig. 98. A, Nephrocytium obesum West, from Angle Tarn, Cumberland. B, N. ecdysiscepanum West & G. S. West, from near Goring, Oxfordshire. C — F, N. hmatum West; C — E, from near Bowness, Westmoreland; F, from near Roundstone, Galway, Ireland. (All x 367.) N. Agardhianum Nag. (inclus. N. Ndgelii Grun.) is A widely distributed species in the stagnant waters of small pools and lakes ; length of cells 12 — 22 JLI ; breadth 7 — 12 /*. N. obesum West is the largest species, characterized by the short, stout cells and by the great thickness of the mother-cell-walls ; length of cells 34 — 42 /* ; breadth 24 — 28 p. ; fig. 98 A. JV. lunatum West is u characteristic species (supposed by Chodat to be a stage of ^V. Agardhianum) which is very local, but sometimes abundant among submerged Sphagnum ; length of cells 14 — 18 p. ; breadth 4 — 6'5 p. ; fig. 98 C — F. JV. ecdysiscepanum Protococcacece 229 W. & G. S. West is a curious species in which the mother-cell-walls throw off a number of integuments, several generations being disposed in a fan-shaped manner and held in position by the partly exuviated layers of the mother-cell- walls; length of cells 24— 26'5 /* ; breadth 13— 17 /i; fig. 98 B. Genus Eremosphaera De Bary, 1858. [Chlorosphcera Hen- frey, 1859.] The cells are solitary, large, and spherical, with a thick, firm cell-wall distinctly differentiated into two layers. Each cell contains a large number of small parietal chloroplasts furnished with a conical projection directed towards the centre of the cell. There is one pyrenoid in each chloroplast. The nucleus is gene- rally contained in a small mass of protoplasm suspended in the Fig. 99. Eremosphcera viridis De Bary, from near Clapham, W. Yorks. ( x 175). central region of the cell by a network of protoplasmic threads. Multiplication takes place by the division of the contents of a mother-cell into two or four smaller but similar daughter-cells (autospores), which are set free by the rupture of the mother-cell- wall. Chodat1 has described the occurrence of certain polymorphic forms of this Alga, but although I have examined large quantities of it from every part of the British Islands, and from elsewhere, I have never yet seen any trace of such forms. Specimens kept under cultivation for two years developed no forms other than globular daughter-cells. Moore2 also disputes the alleged poly- morphism of this Alga. E. viridis De Bary is widely distributed all over the British Islands, more especially in Sphagnum-bogs. It is a constant associate of certain Desmids. The cells vary from 55 — 200 p. in diameter ; fig. 99. Genus Palmellococcus Chodat, 1894. [? Protococcus Ag. 1824 (in part).] The cells are more or less globular, with a firm cell- wall, and aggregated to form a thin mucous stratum. There is in 1 Chodat in Botan. Zeitung, liii, 1895, t. v. 2 Moore in Proc. Amer. Assoc. Adv. Sci. 1900, pp. 278, 279. 230 Chlorophycece each cell a parietal plate-like chloroplast devoid of a pyrenoid, which is often hidden by an orange- red oil. There are three methods of multiplication ; 1st, by division of the original mother-cell into two or four daughter-cells ; 2nd, by a rejuvene- scence of the cell-contents and an exuviation of the wall of the mother- , *n^T\ p^l[ocofccusmini- cell; 3rd, by the formation of 8, atus (Kutz.) Chodat, from near Bradford, w. Yorks. (x720). 16, 32, or 64 spores within the wall of the mother-cell, which then rup- tures and sets them free. Palmellococcus differs from Pleurococcus in the absence of pyrenoids from the chloroplasts, in the methods of reproduction, and therefore in the different aspect of the cell- aggregates. P. miniatus (Kutz.) Chod.1 (Pleurococcus miniatus Nag.) is not an in- frequent Alga on the outer surfaces of plant-pots and similar objects, forming a moist, brownish-green scum, which often turns to an orange-red colour. Diam. cells 2 — 12 -5 /* ; fig. 100. Certain plants belonging to this genus have in the past been referred to "Protococcus Ag." The latter genus is obsolete, having included Algae which are now referred to a number of other genera. Genus Chlorella Beyerinck, 18902. The cells are small, globular or ellipsoid, with firm cell- walls, and with a single parietal chloroplast containing a pyrenoid. They occur in abundance in symbiotic relationship with Hydra viridis, species of Amoeba, Paramoecium, Ophrydium, etc. Multiplication takes place by the quadripartition of the cell contents. Radais3 has confirmed Beyerinck's observations that this Alga has the faculty of cell- increase and the formation of chlorophyll in the dark as in the light. Grintzesco4 also affirms that development takes place more rapidly in total darkness than in full daylight. The latter author has cultivated Chlorella in various media and finds that glucose stimulates its development and that peptone is a better source of nitrogen than nitrates. Cultures of this Alga do not liquefy gelatine. Chi. vulgaris Beyr. is widely distributed and often abundant in cultures or in stagnant aquaria. The cells are 5 — 10 /i in diameter. 1 Chodat in Bull. Herb. Boissier, torn, ii, 1894, pp. 429 and 599. 2 Beyerinck in Botan. Zeitung, xlviii, 1890. 3 Radais in Comptes Rendus, cxxx, 1900, p. 793. 4 J. Grintzesco in Rev. Gen. Bot. xv, 1903. Protococcacece 231 Sub-family V. TETRAEDRIE^l. The plants of this sub-family are always solitary unicells. Each cell is flattened and angular, usually with a definite number of angles, or it is tetrahedral, octahedral, or polyhedral. The angles may be rounded, emarginate, or furnished with spines. Genus Tetraedron Ktitz., 1845. [Polyedrium Nag., 1849.] The cells of this genus, which occur as solitary individuals or rarely collected into temporary aggregates, are flattened and angular (triangular, quadrangular, or polygonal) or polyhedric. The angles are obtuse, acuminate, or furnished with one or more simple or furcate spines. There is a single large chloroplast, parietally disposed and containing one pyrenoid. Multiplication takes place by the formation of four or eight autospores, which are set free by the rupture of the wall of the mother-cell. Sometimes they are expelled into a delicate vesicle, which, however, soon disappears. 0 Fig. 101. A, Tetraedron minimum (A. Br.) Hansg., from Keston Common, Kent. B, T. caudatum (Corda) Hansg., from Pilmoor, N. Yorks. C, T. regulare Kutz., from near Bowness, Westmoreland. D, T, enorme (Ralfs) Hansg., from Mickle Fell, N. Yorks. E— G, T. horridum W. & G. S. West, from Putney Heath, Surrey. (All x 450.) auts, autospores. There are about 14 species of the genus known to occur in the British Islands. T. minimum (A. Br.) Hansg. is the most abundant of the flattened species; diam. of cells 6'5 — 16/*; thickness of cells 5 — 7/x; fig. 101 A. T. regulare Kiitz. ( = Polyedrium tetraedricum Nag.) is the commonest of the polyhedric species ; diam. of cells 13'5 — 40 /* ; fig. 101 C. T. enorme (Ralfs) Hansg. was originally described as a Desmid ; fig. 101 D. The genus Cerasterias Reinsch (1867) is sometimes separated from Tetraedron owing to the depth of the lobulation. The cells are solitary, tetrahedric in character, and the divisions into lobes 232 Chlorophycece are so deep that there is no central body. C. rhaphidioides Reinsch and C. longispina (Perty) W. & G. S. West are both plants of rare occurrence. Sub-family VI. PHYTHELIE.E. This is one of the most interesting sub-families of the Pro- tococcacese, and the Algae contained in it have only recently been brought to light, largely by the plankton investigations of Lemmermann and Chodat. The plants are unicellular or some- times grouped so as to form a more or less definite ccenobium, and in all cases they float freely in the water. As a rule the cells are almost devoid of a mucous envelope, and they are furnished with several stiff bristles considerably longer than their own diameter. Multiplication occurs typically by the formation of autospores, which usually attain all the characters of the adult before their liberation from the swollen wall of the mother-cell. Zoogonidia have been observed in Golenkinia. The name of the sub-family is derived from the genus Phythelios Frenzel (1891), an Alga which was originally described as a Heliozoan. All the genera are practically confined to the plankton of large lakes, although a few of them are occasionally observed in the surface waters of ponds. The long bristles of these Algae are protective characters developed as a result of a free-floating existence amidst numerous animals to which they would other- wise be an easy prey. The genera have been well worked out and monographed by Lemmermann1. Four of them are known from Britain. A. Cells globular. * Cells solitary with evenly distributed bristles Golenkinia. ** Cells in colonies of 8, 16, or more, bristles attached to the outer faces only Richteriella. B. Cells ellipsoid or subcylindrical. * Bristles with a basal swelling Lagerheimia. ** Bristles without a basal swelling Chodatella. Genus Golenkinia Chodat, 1894. The cells are globular, usually solitary, with a firm cellulose wall, which is enveloped in a thin layer of mucilage. Each cell is furnished with a number of radiating bristles of considerable length, evenly disposed over the 1 Lemmermann in Hedwigia, Bd xxxvii, 1898. Protocoecacece 233 outer surface of the cell. There is a parietal chloroplast con- taining one pyrenoid. Multiplication normally takes place by autospores, but also by simple vegetative division, and reproduction by quadriciliate zoogonidia has been observed by Chodat. G. radiata Chodat1 is known from Surrey ; diam. of cells 10 — 15 p. ; length of bristles 25 — 45 /*; fig. 102 D and E. G. paucispinosa West & G. S. West2 is known from the plankton of Lough Neagh, Ireland ; diam. of cells 15 — 16 p. ; length of bristles 16 p.; fig. 102 F. Fig. 102. A, Richteriella botry aides (Schm.) Lemm., after Lemmermann, x 520. B and C, R. botryoides forma quadriseta (Lemm.) Chod. ; B, from the plankton of Lough Beg, Ireland (x450); C, after Lemmermann (x520). D and E, Golenkinia radiata Chod., after Chodat ( x about 800). F, Golenkinia pauci- spinosa W. & G. S. West, from the plankton of Lough Neagh, Ireland ( x 450). Genus Richteriella Lemmermann, 1896. The cells are spherical and generally aggregated to form loose coenobia of 8, 16, 32, or 64 cells. The cell-wall is thin and firm, and is furnished with long, radiating bristles attached only to those surfaces of the cells which face outwards. There is a single parietal chloroplast with one pyrenoid. Multiplication has only been observed to take place by vegetative division. This genus only differs from Golenkinia in the aggregation of the cells and the fact that the bristles are more or less confined to the exposed surface of each cell. 1 Chodat in Morot, Journ. de Bot., Paris, 1894, p. 305, t. iii. 2 West & G. S. West in Trans. Roy. Irish Acad. xxxii, sect. B, part i, 1902, p. 68, t. i, f. 18. 234 Chlorophycece R. botryoides (Schmidle) Lemm., forma quadriseta (Lemm.) Chod. is known from the plankton of Lough Beg, Londonderry, Ireland ; diarn. of cells 3—9-6 fi ; length of bristles 23—60 p. ; fig. 102 B and C. Genus Lagerheimia Chodat, 1895. The cells are solitary, ellipsoid, or subcylindrical with rounded extremities, and with a firm cell-wall. There are four bristles arranged in diverging pairs at each pole, or disposed one at each pole and two equatorially. Each bristle has a wart-like thickening at its base. There is a single parietal chloroplast with one pyrenoid. The multiplication is by autospores. L. subglobosa Lemm. is known from Lough Gartan, Donegal, Ireland (diam. of cells 5'5 — 9'4/x; length of bristles 10'5 — 13 p; fig. 103 D and E), and L. genevensis Chod. from the south of England (diam. of cells 3 p. ; length of cells 9 — 10 p, ; length of bristles up to 16 p ; fig. 103 A— 0). Genus Chodatella Lemmermann, 1898. This genus only differs from the preceding one in the absence of the swellings or wart-like thicken- ings at the base of the bristles. The cells are solitary, ellipsoid, and furnished with four or many elon- gated bristles, which are sometimes radiating and sometimes curved. There may be one or several parietal chloroplasts, with or without pyre- Fig. 103. A — C, Lagerheimia genevensis Chod., after Chodat ( x about 850). D and E, L. subglo- frosaLemm.; D, after Lemmermann (x520); E, from Lough Gartan, Donegal, Ireland ( x 450). F and G, Chodatella breviseta W. & G. S. West, from Lough Gartan, Ireland ( x 450). H and I, Ch. ciliata (Lagerh. ) Lemm. var. amphitricha (Lagerh.) Chod. (x450); H, from Skipwith Common, E. Yorks. ; I, from near Bowness, Westmoreland. auts, autospores. noids. The genus differs from Oocys- tis in the absence of the polar thickenings and the presence of the long spine-like bristles. Ch. ciliata (Lagerh.) Lemm. var. amphitricha (Lagerh.) Chod. [ = Ck. radians (West) Lemm.] occurs in several localities in the British Islands ; length of cells 8—18 /x; breadth 4—13-5 M; length of bristles 12— 20 /x; fig. 103 H and I. Ch. breviseta West & G. S. West is known from Lough Gartan, Donegal, Ireland; length of cells 12— 12'5/x; breadth 8— 9'5/x; length of bristles 11-5— 17"5 M; fig. 103 F and G. Protococcacece 235 Sub-family VII. DICTYOSPH.ERIE.E. This sub-family contains a few genera the affinities of which are somewhat doubtful. The cells are globose, ovoid, or ellipsoid, and are associated to form more or less indefinite colonies. The colony is often of a fragile nature, the cells being held in position by the persistent old walls of the mother-cells, which sometimes become transformed into definite connecting-threads. A copious mucous investment is present in some, but in others it may be entirely absent. The multiplication is by simple vegetative divi- sion or by the formation of four daughter-cells (autospores) within the wall of the mother-cell, which gradually splits open and permits their escape. Reproduction by biciliated zoogonidia has been observed by Zopf and by Massee1 in Dictyosphcerium. The sub-family is most probably an artificial one and perhaps it should not have a place in the Protococcacese. The five following genera are British : — A. Cells indefinitely disposed. * With well-marked, subdichotomous connecting- th reads ; chloroplast parietal Dictyosphcerium. ** Cells in radiating series; connecting threads scarcely visible ; chloroplast axile Dictyocystis. B. Cells grouped in fours in one plane; colonies ir- regular Tetracoccus. C. Cells in botryoidal clusters. * Freely exposed in a thin gelatinous envelope Botryococcus. ** Clusters covered by a firm, irregular, tough membrane Ineffigiata. Genus Dictyosphaerium Nag., 1849. The cells are globose, ovoid, or subreniform in shape, with a firm cell-wall, and they are connected by dichotomously branched threads to form a roughly spherical or ellipsoidal colony. The entire colony is enveloped in mucus, and the cells are situated somewhat far B apart towards its periphery, large Fig. 104. Dictyosphcerium pui- colonies often becoming very irregu- chellum Wood. A, from the plank- }ar. Each cell contains a more or ton of Loch Shin, Sutherland; B, , n , j • . i ri i from Cam Fell, W. Yorks. x 450. less bell-shaped, parietal chloroplast, 1 G. Massee in Journ. Linn. Soc. Bot. xxvii, 1891. 236 Chlorophycece furnished with a single pyrenoid. The connecting-threads are often derived from the old mother-cell-walls, but in some cases it is doubtful if they do arise in this manner. Multiplication takes place normally by the formation of four daughter-cells within the mother-cell. Reproduction by biciliated zoogonidia occurs, but has been very rarely observed. D. Ehrenbergianum Nag. is a widely distributed British Alga, often occurring in quantity in the surface waters of ponds and in the plankton of lakes ; diam. of cells 4 — 10 p. D. pulchellum Wood (fig. 104), D. reniforme Buln. and D. oviforme Lagerh. are more rarely found, but it is probable that the five so-called species of this genus are merely forms of D. Ehrenbergianum. Genus Dictyocystis Lagerh., 18901. The cells are ellipsoid or oblong, and are arranged in radiating series to form a small free-floating colony. The radiating series of cells frequently branch and the cells are held in place by delicate mucous threads. Each cell possesses a central chloroplast with one pyrenoid. D. Hitchcockii (Wolle) Lagerh. is a rare British Alga, occurring in the bogs of N. Ireland and N. W. Scotland, and also in the Scottish plankton. Diam. of cells 9 — 11 fj.; the American specimens are larger. Genus Tetracoccus West, 18922. [Westella De Wild., 1897 (in part).] The cells are small, globose or subglobose, sometimes a little angular, and are closely arranged in groups of four. These groups are connected by the old mother-cell-walls into free-floating colonies of small size, consisting of a maximum number of about 80 cells. The four cells of each group are disposed in one plane, and the old walls of the mother- cells become transformed into deli- cate connecting-threads. There is one chloroplast which contains several large granules, but the presence of pyrenoids has not yet been definitely demonstrated. Multiplication takes place by the formation of four daughter-cells within the mother-cell, which arise by the division of the cell- contents in two directions in one plane. The colonies are almost entirely free from enveloping mucus. 1 Lagerheim in Nuovo Notarisia, 1890, p. 226. 2 West in Journ. Boy. Micr. Soc. 1892, p. 735, t. x, f. 43—48. Fig. 105. Tetracoccus botryoides West, from Bowness, Westmoreland. A and B, x450; B and C, two "te- trads," x715. Protococcacece 237 Schmidle1 gave what he termed an 'amended description' of this genus in 1894, but as the plant he included in it is not a species of Tetracoccus, his amended description is not a correct one2. T. botryoides West is widely distributed in the British Islands, generally occurring in the surface waters of ponds and in the plankton of large lakes. Diam. of cells 3'8 — 57 /* ; diam. of colonies 30 — 57 /*; fig. 105. Genus Botryococcus Kiitz., 1849. The colony is free-floating and consists of an aggregate of botryoidal groups of cells. The cells are globose or ovoid in form and are closely aggregated to form clusters of 16 or 32 cells, the clusters being held together partly by old mother-cell-walls and partly by a gelatinous investment. There is a single cup-shaped chloroplast in each cell, but pyrenoids have not been observed, Chodat and Cretier3 have Braunii Kiitz'., observed in the chloroplast a Small Forest, Hants. A, small colony; r i i • i , B, two isolated cells ( x 450). body which can be regarded as a pyrenoid without an amylosphere. As a rule this Alga is of a bright green colour, but when occurring in large quantity, as it frequently does in the freshwater plankton, the cells become filled with a brick-red oil. B. Braunii Kiitz. is the best known representative of the genus, and is a frequent plant in bog-pools, large ponds, lakes, etc. Diam. of cells 5'5— 9 p. ; tig. 106. B. sudeticus Lemm. (which may only be a form of B. Braunii with globose cells) and B. calcarem West are rarer British species. Genus Ineffigiata West & G. S. West, 1897; em. 1903. This Alga consists of free-floating colonies of very irregular form and destitute of a gelatinous investment. The colony is composed of several families of cells agglutinated together, each family being small, more or less spherical, and consisting of a peripheral layer of cells surrounding a central cavity. The cells are ellipsoid or ovoid in form, and each one is furnished with a parietal chloro- plast, often containing what has been described as a single small 1 Schmidle in Flora, 1894, Heft 1, p. 45. '2 Vide West & G. S. West iu Journ. Eoy. Micr. Soc. 1896, p. 162. 3 Chodat & Cretier in Arch. Sci. Phys. et Nat. x, 1900. 238 Chlorophycece pyrenoid, but which I am inclined to believe is a small granule of starch. In some cells starch appears to be quite absent. The outer surface of each family of cells is enveloped in a tough elastic membrane of irregular form, which contains a trace of cellulose, and is folded and produced into all manner of irregular wrinkles, lobes, pro- cesses and spines. Sometimes these irregular projections are wanting, but at other times they are exceedingly nume- rous. The membrane is a secretion of the underlying cells, and its presence renders observations on this Alga more difficult than on any other of the Protococcaceae. Sometimes the smaller colo- nies are united by more or less rigid prolongations of the enveloping membranes into much larger colonies. The families multiply by division, forming larger and larger colonies, which ulti- mately become separated into smaller groups by the develop- ment of elongated processes of the enveloping membranes. The reproduction is unknown1. In situations in which Ineffigiata occurs in quantity, such as in the freshwater plankton, the cells develop the brick-red oily material which is found in the preceding genus. /. neglecta W. & G. S. West is one of the most widely distributed of British Algae, occurring in all kinds of situations — in ditches, bogs, tanks, water- butts, etc. — and forming a regular and considerable constituent of the fresh- water plankton. Diam. of single families 21 — 56 p., of colonies 46 — 350 p. ; length of cells 5-7—10-5 p., breadth 3'4— 5'3 p. ; fig. 107. 1 Vide Journ. Bot. March, 1903, t. 447, f. 1—6. Fig. 107. Inefficfiata neglecta W. & G. S. West, from Harris, Outer Hebrides. A, outline of colony ; B, smaller colony ; C, part of single family in section; D, snowing escape of cells from a small colony. Palmellacece 239 Family 8. PALMELLACEiE. The Palmellacese is one of the most primitive families of green Algae, primarily distinguished from the other groups of the Protococcoideae by the indefinite colonies of cells enveloped in a conspicuous mass of mucilage. In the ordinary vegetative con- dition these plants present the appearance of a group of more or less irregularly disposed cells embedded in a copious mass of jelly, which is either structureless or differentiated into concentric envelopes. The colonies are either microscopic or macroscopic, and sometimes reach a length of several centimetres. The cells are globose or ellipsoid, of small size, and are frequently arranged in pairs or in groups of four. Sometimes these groups of four or ' tetrads ' are disposed in a tetrahedral manner, but at other times they are situated in one plane. Each cell contains a somewhat bell-shaped chloroplast which may or may not be furnished with a pyrenoid. The nucleus is situated in the hollow of the chloroplast. In some genera (e.g. Tetraspora and Apiocystis) each cell is furnished with a pair of ' pseudocilia,' which consist of long motionless protoplasmic threads penetrating through the enveloping mucus to the exterior. These were first discovered by Thuret. Multiplication takes place by cell-division in two or three directions, followed sooner or later by a diffluence of a large part of the enveloping mucus and the consequent dismemberment of the colony into smaller portions, each of which increases as before either by simple cell-fission or by the formation of two or four daughter-cells within each mother-cell. Asexual reproduction takes place by biciliated zoogonidia. The latter are formed either by the transformation of a vegetative cell into a zoogonidangium in which several zoogonidia arise, or by the assumption by the ordinary vegetative cell of the motile Chlamydomonadine condition. The motile state greatly resembles, the Chlamydomonad-type, and these plants have no doubt arisen by the intercalation of a simple though well-marked vegetative condition between two successive motile phases. Sexual reproduction has been observed in some of the Palmel- laceae. It consists of a fusion of isogamous planogametes, either similar in all respects to the zoogonidia and produced singly in a 240 Chlorophycece gametangium, or much smaller than the zoogonidia and produced in numbers from a gametangium. In some of these plants the colony has no definite form, but in others the- cells, although irregularly grouped, are contained in a mucous mass which invariably assumes a definite shape. The family can be divided into three sub-families, in each of which the mucus may be indefinite or developed in accordance with some definite plan. Sub-family I. Palmellece. Cells irregularly grouped within a structureless mass of mucus. Sub-family II. Tetrasporece. Cells grouped in fours or sometimes irregularly disposed at the periphery of a structureless mass of mucus. Each cell with two pseudocilia. Sub-family III. Oloeocystidece. Cells grouped in twos or fours within a lamellose mucous investment. Sub-family I. PALMELLE.E. This sub-family is characterised by the large number of globose cells which are irregularly grouped within a structureless mass of mucus. The latter is usually of indefinite extent, but in Palmo- dactylon it is more or less cylindrical and often much branched. The cell-walls are generally firm and thin, and in Schizochlamys the outer layers are periodically thrown off in one or several pieces. Genus Palmella Lyngb., 1819. The cells are spherical, with thin cell-walls, and they are surrounded by mucous coats which have fused to form an indefinite mass of jelly. The parietal chloroplast contains a pyrenoid. Multiplication takes place by repeated bipartitions of the cells in all directions of space, ac- companied by an extreme gelatinization of the mother-cell-walls. Reproduction occurs by macrozoogonidia, by microzoogonidia, and by small isogamous planogametes. One of the few true species of this genus is P. miniata Leibl., which occurs as a mucous expansion of a brick-red colour on damp ground, wet rocks, etc. ; diam. of cells 3 — 5 p.. P. mucosa Kiitz. and P. hyalina Breb. are aquatic species of a green colour ; the former may possibly be a state of Tetraspora. Genus Palmodactylon Nag., 1849. This is a well-marked genus of the Palmellea3, differing from Palmella mainly in the definite form of the enveloping jelly. The chloroplast is parietal and irregularly lobed, but is destitute of a pyrenoid. Multiplication of the cells takes place in all directions, but preponderates in 241 one direction, so that the cells are grouped irregularly within a cylindrical mass of mucus. This cylindrical mucous envelope frequently branches, each branch being similar to the „ &> D ~-<5> B Fig. 111. Tetraspora lubrica (Roth) Ag., from near St Just, Cornwall. A, nat. size; B, portion of colony, x 100 ; C, x450; D, zoogonidium, x 450. cells are similar to those of Palmella, with the addition of two (or more rarely four) ' pseudocilia.' Multiplication takes place by repeated division of the cells, chiefly in two directions in one plane, with the gelatinization of the mother-cell-walls. Reproduc- tion occurs by biciliated zoogonidia and isogamous planogarnetes. Hypnospores, 'with thick cell- walls of a brown colour, are also produced. Several 'species' of this genus occur in the stagnant waters of the British Islands, but it is very doubtful if they are specifically distinct. T. gelatinosa (Vauch.) Desv. is the commonest form, with a vesicular gelatinous colony and cells 6 — 12 /i in diameter. T. lubrica Ag. (fig. Ill) and T. explanata Ag. are most probably other forms of this species. T. lacustris Lemm., which is a form confined to the plankton, is possibly a stage in the life-history of Sphcero- cystis Schroeteri Chod. 16—2 244 Chlorophycece Genus Apiocystis Nag., 1849. The gelatinous colonies are relatively small and attenuated towards the base, which is usually fixed to other larger Algae. The cells are similar in structure to those of Palmella, and they are disposed without order near the periphery of the gelatinous vesicle. Each cell is furnished with two ' pseudocilia,' which penetrate through the jelly into the surround- ing water. Multiplication occurs by the division of the cells in two or three directions accompanied by a corresponding in- crease in the size of the colony. Correns1 states that when a cell divides one pseudocilium goes to each daughter-cell, a second one being subse- quently developed. Re- production takes place by biciliated zoogonidia and isogamous gametes2. Fig. 112. Apiocystis Brauniana Nag., from near Bowness, Westmoreland ( x 400). A. Brauniana Nag. is not uncommon in ponds, ditches, bog-pools, etc., and its pyri- form colony is commonly attached by the base to larger filamentous Algse. The colonies are 12 — 1000 p. (or upwards) in length and the cells 6 — 8 p. in diameter; fig. 112. Sub-family III. GLCEOCFSTIDE^. The colonies of this sub-family consist of an aggregate of cells within a common mucilaginous envelope, which exhibits a lamellose structure. As a rule concentric coats of mucus can be distinguished round each individual cell or round a small group of daughter- cells. The lamellation of the mucous integument reaches a 1 Vide Bot. Centralbl. liv, 1893, p. 146. 2 Moore in Journ. Linn. Soc. Bot. xxv, 1890. 245 maximum in some species of Glceocystis. Multiplication occurs principally by a tetrahedric division of the mother-cells, accom- panied by a gelatinization of the mother-cell-walls. Reproduction also takes place by biciliated zoogonidia. Genus Gloeocystis Nag., 1849. [Chlorococcum Fries, 1825 (in part).] The plants occur as small irregular colonies consisting of Fig. 113. A — E, Gloeocystis infusionum (Schrank) W. & G. S. West, from Barnes Common, Surrey. F — H, Gl. gigas (Ktitz.) Lagerh., from Wimbledon Common, Surrey. (All x420.) an indefinite group of cells formed by the successive division of the mother-cells. The enveloping mucus generally shows a 246 Chlorophyceee marked lamellation, similar to that exhibited by Glceocapsa among the Myxophycese. The cells are globose or ellipsoid, with a parietal bell-shaped chloroplast furnished with one pyrenoid. The most abundant species is Gl. gigas (Kiitz.) Lagerh. [ = Chlorococcum gigas Grun. ; Glceocystis ampla (Kiitz.) Rabenh.], which is found in stagnant waters among other Algae; the cells are globose and 10 — 17 p. in diameter; fig. 113 F — H. G. vesiculosa Nag. is also a very common species of the genus in which the cells are ellipsoid and 4 — 12 p. in diameter. Gl. infusionum (Schrank) W. & G. S. West [ = Chlorococcum infusionum (Schrank) Menegh.] is a large species in which the lamellation of the integument is most remark- able ; diam. of cells 25 — 30 p. ; diam. of integuments of a single cell often 180 p.; fig. 113 A — E. There are several other so-called 'species' of this genus, but they are of doubtful value. The genus Capsulococcus Bennett (1888) is of very doubtful character and possibly does not belong to the Algse. C. crateriformis Benn. was described from the English Lake District. Genus Dactylothece Lagerh., 18831. This genus closely resembles Gloeocystis in the general arrangement __ of the colony, but the Q cells are oblong-ellipsoid ft and division only takes place in one direction. The chloroplast is a pari- Fig. 114. Dactylothece Braunii Lagerh., etal plate only occupying A, from near Bradford, W. Yorks. ; B — D, from i . i • j i- .Li- near Senens, Cornwall ( x 420). about two-thirds of the cell and destitute of a pyrenoid. The lamellation of the integuments is frequently in- distinct. D. Braunii Lagerh. occurs in damp situations and also in stagnant pools. The cells are 7'5 — 10*5 p. in length and 3'5 — 4'8 p. in breadth ; fig. 114. Genus Palmodictyon Kiitz., 1845. The colonies of this genus are very remarkable, the groups of cells and their surrounding integuments being arranged in cylindrical masses, which branch and anastomose with each other. The external mucous coats of these elongated colonies often become very tough and assume a reddish-brown colour. Reproduction occurs by the formation of resting-spores or hypnospores with brown cell- walls. The germi- 1 Lagerheim in Ofvers. af K. Sv. Vet.-Akad. Forh. 1883, no. 2, t. 1, f. 22—24. nation of these resting-spores results almost immediately in the formation of an elongated colony. Palmodictyon viride Kiitz. is a very rare British Alga which I have only observed from the extreme south-west of England. The cells are globose and 5*5 — 9 fi in diameter ; the cylindrical colonies vary from 28 — 52 p. in diameter ; fig. 115. CL, A Fig. 115. Palmodictyon viride Kiitz., from near St Just, Cornwall ( x 420). A, part of adult, branched colony; B and C, young colonies. Genus Botrydina Breb., 1839. The colonies consist of sub- spherical aggregates of cells of the Gloeocystis-type, enveloped in a thick gelatinous integument which may reach a diameter of 500ft. The genus requires further investigation. B. vulgaris Breb. occurs amongst mosses on damp ground, on the trunks of trees, etc. The cells are globose or ellipsoid and 2 — 7 p in diameter. It sometimes occurs in large quantity amongst Leucobryum glaacum. Class 4. HETEROKONT^:. THIS class has been recently established by Luther to embrace a number of Algae which were for a long time regarded as members of the Chlorophycese. They are yellow-green in colour owing to the presence of a large quantity of xanthophyll in the chromatophores, and the product of metabolism is an oil. The class was instituted to include two series of organisms, one of which, the ' Chloromonadales,' is distinctly a group of the Flagellata, including certain primitive Flagellate organisms from which the rest of the Heterokontse have been evolved. Bohlin, and also Black man and Tansley, place the genus Vaucheria in this class under a third series, the ' Vaucheriales ' ; but I have preferred to retain this genus in the Chlorophycese in the old family VaucheriaceaB of the Siphoneae. Excluding Vaucheria and the Flagellate group Chloromonadales, the rest of the Heterokontse fall under the order ' Confervales ' proposed by Borzi in 1889, and they are all strictly algal in organization. They are unicellular, multi- cellular, or coanocytic in character, exhibiting a considerable variety of form, and occurring as simple rounded unicells, long multicellular filaments, or large gregarious coenocytes. The cells usually contain many chromatophores (rarely only one), which are discoidal in form, of a yellow-green colour, and devoid of pyrenoicls and starch. In other respects the cell-structure is similar to that described for the Chlorophycese. Multiplication by cell-division does not take place in some genera. The usual method of asexual reproduction is by zoogonidj^a of a somewhat peculiar character. They are generally ovoid or pear- shaped and are furnished with two cilia. The latter have only been accurately examined in a few genera and have been found to be of unequal length. They are attached to one side of the Heterokontce 249 anterior extremity of the zoogonidium and are generally carried in opposite directions. Each zoogonidium usually possesses several parietal chromatophores (vide fig. 121 C). Aplanospores are also frequently formed, usually one in each cell and possessed of thick cell-walls. Sexual reproduction occurs by the fusion of isogamous plano- gametes which most probably resemble the zoogonidia in the possession of two unequal cilia1. It is only very recently (1898) that the second short cilium was demonstrated, up to that time the zoogonidia and gametes of these AlgaB having been described as possessing only one cilium. The second short cilium is usually carried in a backward direction, pressed closely against the body of the cell. The Heterokontse contains only a limited number of genera. None of the Flagellate series 'Chloromonadales' have been observed from the British Islands, and all the remaining genera belong to the Confervales. Chlorobotrys Bohlin, which that author referred to the Chloromonadales, is strictly algal in character and belongs to the Tribonemaceae. Order I. CONFERVALES. In this order the cells are entirely algal in character, thus differing from those of the Flagellate order Chloromonadales. The plants are unicellular, multicellular, or crenocytic, and the cell-walls are sometimes very thick. Each cell contains several or many discoidal chromatophores, with a parietal disposition, and from which pyrenoids are absent. The reproduction is by zoogonidia and isogamous planogametes, the former possessing a pair of unequal cilia. The order is divided into three families : — Family 1. Chlorotheciacece. Unicellular or colonial; cells small, often attached by basal stalks, uninucleate, with one or many chro- matophores. Family 2. Tribonemacece. Unicellular or filamentous ; cells often elongate, uninucleate or subccenocytic, with several or many chromato- phores ; cell-walls firm and thick. Family 3. Botrydiacece. Plant-body large and coanocytic, fixed, with well-developed organs of attachment ; chromatophores numerous. 1 Gametes have been described in certain genera with two equal cilia, but such statements are not established facts and require re-investigation. 250 Heterokontce Family 1. CHLOROTHECIACE^. In this family the plants are very small, unicellular, gregarious, or colonial. The solitary and gregarious cells are attached each by a basal stalk, generally to some larger filamentous Alga, but in the colonial forms the cells are united by mucilaginous bands or stalks. Each cell contains a single nucleus and one or many parietal chromatophores. Multiplication takes place in some genera by vegetative division, but not in others. Reproduction occurs by zoogonidia and isogamous gametes, with one long cilium arid most probably a shorter one, the presence of which has not yet been ascertained. The three following genera are known as British : — A. Cells stalked ; no vegetative division. * Cells gregarious, living in the mucilaginous invest- ments of other Algae and attached by a stalk of extreme tenuity ; with one chromatophore Stipitococcus. ** Cells ovoid, rounded, or ellipsoid, attached by a thick stalk ; chromatophores several or many Characiopsis. B. Cells united to form branched colonies by tubular stalks of mucilage; vegetative division abundant... Mischococcus. Genus Stipitococcus West & G. S. West, 18981. The cells are very minute, gregarious, and epiphytic on other filamentous Alga3, being embedded in the mucilage surrounding the fila- ment, to which they are attached by long stalks of extreme fine- ness. In shape the cells are ovoid and apiculate, or somewhat campanulate, with a rounded base and an attenuated or ir- regularly expanded apex. There is a single parietal chloroplast of a pale green colour, somewhat irregular in form and curled round the inner surface of the cell- wall. A single small nucleus is present in the centre of the cell. Reproduction is by zoogonidia, 1 West & G. S. West in Journ. Bot. Sept. 1898. Fig. 116. Stipitococcus urceolatus W. & G. S. West ; A— C, epiphytic on a filament of Mougeotia, from Oughter- shaw Tarn, W. Yorks. ; A, x500; B and C, x 780 ; D, epiphytic on Sphtero- zosma excavatwn, from Harris, Outer Hebrides (x500). Chloro theciacece 251 two of which are produced from each mother-cell. Only one long cilium has been observed on the zoogonidia, but it is very probable that another shorter one has been overlooked. The zoogonidia become attached by the end of the long cilium, the latter then forming the stalk of the new unicellular plant. The genus closely resembles Peroniella Gobi1, which is also an epiphyte, occurring in the mucous investments of Hyalotheca. The cells are, however, smaller than in that genus and their apices are acute or expanded. The general form of the cells is thus different from the rounded cells of Peroniella. S. urceolatus West & G. S. West is known from W. Yorkshire and from N. W. Scotland, occurring as an epiphyte on Mougeotia and Sphcerozosma ; diam. of cells 3 — 4'2 p. ; length 6'5 — 10'5 p. ; length of hyaline stalk 4 — 6 p. ; fig. 116. Schmidle2 has described another species from Germany. Genus Characiopsis Borzi, 1895. Most of the plants of this genus were at one time described as species of Characium A. Br. The cells are rounded, ellipsoid, or ovoid, sometimes acuminate at the apex, with a firm cell-wall and a short basal stalk of some thickness. They occur as epiphytes, solitary or gregarious, and there is no vegetative division. Each cell contains several or many small, parietal chroma- tophores of a pale-green colour. Repro- duction occurs by the division of the cell- contents either to form eight (or more?) zoogonidia, which are set free by the disso- lution of the upper portion of the mother- cell-wall, or to form a number of globose aplanospores which become gametangia immediately on liberation, each producing two or four gametes. There are a number of species, several of which are known from Britain. Ch. minuta (A. Br.) Borzi is the most frequent; length of cells 17 — 18 p.; breadth 5-5 p. ; fig. 117 A. Ch. turgida W. & G. S. West is the largest species of the genus; length of cells 36— 46 p.; breadth 11'5— 16 p.; fig. 117 B— D. Genus Mischococeus Nag., 1849. The cells are globular and are united by thick tubular stalks of mucilage to form small 1 Gobi in Scripta Botan. Horti Univers. Imp. Petropolitanae, torn, i, 1866-7, pp. 244—250, t. 1. 2 Schmidle in Hedwigia, Bd xli, 1902, Heft 4, p. 153, fig. A 1. B ^ C -^ D Fig. 117. A, Characi- opsis minuta (A. Br.) Borzi, from near Peuzance, Corn- wall. B — D, Ch. turgida W. & G. S. West, from Keighley Moor, W. Yorks. ( x 500). 252 Heterokontce branched colonies ; they are situated only at the extremities of the mucous tubes and each possesses from one to four chromatophores. Reproduction takes place by zoogonidia and isogamous piano- gametes. The zoogonidia usually germinate directly to form a small typical colony, but the zygospore divides in two directions in one plane forming an epiphytic cushion, all the cells of which are situated on short, broad, mucilaginous stalks. Fig. 118. Mischococcus confervicola Nag. A, from Cam Fell, W. Yorks.; B and C, from Kuislip Keservoir, Middlesex ( x 500). M. confervicola Nag. is a rather uncommon Alga, occurring as an epiphyte on various filamentous species of Cladophoracese, Tribonemacese, Ulotrichacese, CEdogoniacese, etc. It is generally found in small ponds and ditches, or more rarely in peaty pools ; diam. of cells 3'5 — 5'5 p.; fig. 118. Another genus belonging to the Chlorotheciacese has been recently described by Schmidle1 under the name of Oodesmus. Lemmermann reports having found this genus in some plankton material forwarded to him from Loch Doon, Ayrshire. The cells are ovoid and united by short bands of mucus to form free- swimming colonies. Each colony consists of four cells, which are disposed in one plane. The cell-wall is relatively thick and there are one or two chromatophores in each cell. 0. Doederleinii Schmidle is the only known species ; cells 8 /* in length and 6 /* in breadth. 1 Schmidle in Hedwigia, Bd xli, Heft 4, 1902, p. 162, fig. B 4. Tribommacece 253 Family 2. TRIBONEMACEJE. The plants of this family are unicellular or filamentous. The cells are globose, cylindrical, elongate, often spirally coiled or united to form long flexuose filaments. There is generally a single nucleus in each cell, but sometimes two or more are present, giving the cell a more or less crenocytic character. The cell-walls are always firm and usually of some thickness, except in the genus Buinilleria, in which the walls sometimes become swollen and hyaline. Asexual reproduction takes place by zoogonidia with one long and one short cilium, and two or several parietal chromato- phores. Aplanospores are also of frequent occurrence in the genus Tribonema. Sexual reproduction occurs by isogamous piano- gametes which have been described, but perhaps erroneously so, as having two equal cilia. There are four British genera, three of which are abundant. A. Plants unicellular. * Cells globose, aggregated in mucilaginous colonies . . . Chlorobotrys. ** Cells elongate, usually shortly stipitate and often spirally coiled Ophiocytium. B. Plants filamentous. * Cell- walls firm, splitting into H -pieces Tribonema. ** Cell- walls hyaline, H -pieces not very evident; fila- ments small Bumilleria. Genus Chlorobotrys Bohlin, 19021. The cells are globose or subglobose, solitary, or more commonly aggregated in families of 2, 4, 8, or 16. Each family is surrounded by an ample mucous integument, very hyaline and quite homogeneous. The cell-walls are firm, smooth, of some considerable thickness, and they contain a certain proportion of silica. The chromatophores are parietal, yellow-green discs, from 6 to 30 of which are disposed on the walls of each cell. Sometimes the pigment becomes more or less diffuse. There is frequently a prominent red pigment-spot in each cell of the family, but sometimes this is entirely absent. Multiplication takes place by the division of the cells primarily in two directions, but afterwards in three directions2. Families of 4, 8, or 16 cells are therefore frequently very symmetrical, but beyond this number they become irregular. During cell-division the contiguous walls 1 Bohlin in Bihang till K. Sv. Vet.-Akad. Handl. Bd 27, no. 4, 1902, p. 34, t. i, f. 9. - West & G. S. West in Journ. Bot. April, 1903. 254 Heterokontce Fig. 119. Cklorobotrys regular-is (West)B'ohlin, from Tremethick Moor, Cornwall ( x 450). of the daughter-cells are at first much flattened, but afterwards become more convex. Zoogonidia have not been observed. Bohlin was distinctly in error in referring this Alga to the Chloromonadales, as the plants are strictly algal in character. The ordinary vegetative condition of the orga- nisms belonging to the Chloromonadales is a ciliated or flagellated one, whereas a motile condition of Chlorobotrys has never been observed. Moreover, Chlorobotrys is a very abundant Alga and one which I have had under observation for many years ; and the motile condition, far from being the ordinary state of the plant, must be exceptionally rare. The genus is undoubtedly nearest to Botrydiopsis Borzi, but differs in the smaller size of the cells, which are associated to form colonies, and the prominent mucous investment. Moreover, it is only found in still water, whereas Botrydiopsis inhabits running water. Chi. regularis (West) Bohlin [Chlorococcum regulare West1] is widely dis- tributed and often abundant in the Sphagnum-bogs of the British Islands. I have also examined numerous specimens of it from Norway, Switzerland and the United States. The cells are 12 — 19 p. in diameter and the families (with the mucous investments) are 34 — 90 p. in diameter; fig. 119. Genus Ophiocytium Nag., 1849. [Indus. Sciadium A. Br., 1855.] The cells are free or attached and generally many times longer than the diameter. They are commonly solitary, but sometimes colonial, and they are usually curved or spirally con- torted. The apex of the cell may be capitate or apiculate and is sometimes attenuated into a long spine. Each cell contains several nuclei and a number of large parietal chromatophores of a somewhat cylindrical form. The presence of oil drops is a feature of some species. The cell- wall consists of a homogeneous lid fitted to the apex of a long tube composed of apposed layers of pectose 1 West in Journ. Roy. Micr. Soc. 1892, p. 737, t. x, f. 55. Trfbottemacece 255 compounds. Vegetative division does not occur. Asexual repro- duction takes place by the division of the cell-contents to form ellipsoidal aplanospores, or to form eight ovoidal zoogonidia with two cilia. In those species which are at- tached the zoogonidia generally come to rest on the rim of the empty tube-like cell and there grow into adult cells. A repetition of this pro- cess produces a curious branch-system. Some- times the zoogonidia develop on the apices of other cells which contain the cell-con- tents. No gametes have been observed. The genus was monographed by Lemmermann1, but the validity of the thir- teen species he puts forward is questionable. Fig. 120. A, Ophiocytium majus Nag., from Bowness, Westmoreland. B — G, O. cochleare (Eichw.) A. Br. , from same locality. H and I, 0. bicuspidatum (Borge) Lemm. forma longispina Lemm. , from Pilmoor, N. Yorks. J, O. Arbus- cula (A. Br.) Eabenh., from Mitcham Common, Surrey. (All x450.) K, 0. graciliceps (A. Br.) Babenh., after treatment with potassium hydrate (after Bohlin, x 570). Several species are widely distributed in the British Islands. 0. Arbuscula (A. Br.) Rabenh. is an attached species, often with very pretty branch- systems ; diam. of cells 3 — 8 p. ; fig. 120 J. 0. majus Nag. is the largest species, the cells reaching a diameter of 17 /* ; fig. 120 A. 0. cochleare (Eichw.) A. Br., 0. capitatum Wolle, 0. bicuspidatum (Borge) Lemm. and 0. parvulum (Perty) A. Br. are also frequent species. Genus Tribonema Derbes & Solier, 1856. {Conferva in the sense used by Lagerheim, 1888.] The plants of this genus are simple filaments of cylindrical or slightly barrel-shaped cells with strong cell-walls. The latter are often of considerable thickness and the filaments frequently break up into H -pieces. Each H -piece consists of a transverse cell- wall with a cylindrical piece on either side, and the whole is composed of a number of layers of pectose compounds. Each cell is thus bounded by the halves of two H -pieces. The cells contain one (or sometimes two) nuclei and a variable number of parietal chromatophores. In some 1 Lemmermann in Hedwigia, Bd xxxviii, 1899, pp. 20 — 38, t. iii & iv. 256 Heterokontm species the chromatophores are few and irregular, but more often they are numerous and discoidal. Asexual reproduction takes place by the formation of globular or ellipsoidal aplanospores, which escape by the breaking up of the filament (fig. 121 B and I); also by zoogonidia with a pair of unequal cilia (fig. 121 C). Sexual reproduction occurs by the conjugation of isogamous gametes, but the conjugation is not strictly isogamous, as one gamete conies to rest and rounds itself off before another swarms up to it and conjugates with it. The structure of the cell-wall of this genus was well described by Bohlin1, who also demonstrated the close affinity between Tribonema (Conferva Lagerh.) and Ophiocytium. Concerning the abandonment of the generic name ' Conferva,' I cannot do better than quote at length the remarks recently made by Hazen2. He writes : — " The name Conferva is very ancient, going back to the time of Pliny. As a modern generic name it has received most varied treatment, and covered at different times very diverse groups of plants. "Under this name Linnaeus included a very large part of the branching, as well as the simple, filamentous algae. He adopted the genus from Dillenius. The first species mentioned by Linnaeus, Conferva rivularis, is undoubtedly the oldest of his group, so far as the history of these ill-defined forms can be determined. This species, according to the synonymy of Linnaeus (Sp. PI. 1164. 1753), is Conferva Jiumatilis, sericea vulgaris et fluitans of Dillenius (Hist. Muse. 12, pi. 2, f. 1. 1741) ; this in turn is Conferva Plinii Dillen. (Cat. Plant, sponte Gissam nascentium, 199. 1719); the earliest description of C. Plinii that Ave have seen is in L'Obel's Plantarum Observationes, 664. 1576, but undoubtedly the name is of more ancient origin. "Now no one would imagine that the ancient herbalists or even Linnaeus could distinguish the numerous filamentous forms known to us only by the use of good microscopes. Indeed, the fact that Linnaeus described only two un branched species is sufficient proof of this. Conferva rivularis as collected by him, was very likely at one time a Spirogyra and at another time an (Edogonium. This type species, however, as interpreted by the earlier algologists, e.g., Dillwyn, Lyngbye and Mueller, is evidently a form belonging to what is now known as Rhizoclonium, and has come down to us as R. rivu- laris (L.) Kiitz. This identification is also confirmed by Linnaeus himself, who (Sp. PI. Ed. 14. 1784) quotes the figure of C. rivularis from Flora Danica. "At any rate, there is no warrant whatever for employing the name Con- ferva to designate the genus recognized under that name in Lagerheim's revision, for there is no evidence that these species were ever collected by 1 Bohlin in Bihang till K. Sv. Vet.-Akad. Handl. 1897, Bd 23, no. 3. 2 Hazen in Memoirs Torr. Bot. Club, xi, 1902, no. 2, pp. 181—183. Tribonemacece 2.57 Linnseus, and certainly none of them were distinguished by him from other simple filamentous forms. "For Lagerheim's group of species, as for all genera, the adoption of a generic name based on a recognizable species, as a type, is essential. The Fig. 121. A — G, Tribonema bombycinum (Ag.) Derb. & Sol. ; A, from Shipley, W. Yorks. ; B, showing aplanospores (a^), from Senens, Cornwall; C, zoogo- nidium, and D — F, young plants, from Senens, Cornwall (all x 450) ; G, after treatment with potassium hydrate (after Bohlin, x 570). H and I, T. bomby- cinum forma minor (Wille) nob. ; H, from Shipley, W. Yorks. ; I, showing aplanospores (op), from near St Just, Cornwall ( x 450). J, Bumilleria pumila W. & G. S. West, from near Senens, Cornwall ( x 450). earliest such name in the present case is Tribonema Derbes & Solier (1856) l. This genus was based on a single species, Conferva bombycina, and in the diagnosis, for the first time in the history of the species, explicit mention was made of the most essential character, namely, the form of the chromatophores, although it had been previously suggested in the plates of Kutzing. The method of zoospore dispersal was also first described and illustrated by Derbes & Solier. There is, then, every reason for employing the name Tribonema as a memorial of the discernment of these authors." 1 Derbes & Solier, Me"m. sur quelques points de la physiologie des Algues, 1856. W. A. 17 258 Heterokontce T. bombycinum (Ag.) Derb. & Sol. ( = Conferva bombycina Ag.) is general throughout the British Islands; diam. of cells 8 — 15 p.; fig. 121 A — G. A small form of this species [forma minor (Wille) nob.J is also very common ; diam. of cells 5 — 6*5 p.: fig. 121 H and I. T. affine (Klitz.) nob. ( = Conferva ajfinis Kiitz.) is the thinnest species with the most elongate cells, and the chromatophores are few and irregular; diam. of cells 5 — 5'4 p.. T. obso- letum nob. ( = Conferva obsoleta West & G. S. West) is a much rarer species ; diam. of cells 19—21 p.. Genus Bumilleria Borzi, 1895. The cells of this genus are arranged in long filaments which differ from those of Conferva principally in the structure of the cell-wall. The latter is practically homogeneous and does not readily break into H -pieces. The pectose constituents instead of forming closely apposed layers may form a distinct mucous cylinder in which the cells appear to be embedded. The chromatophores are small, pulvinate and parietal. B. pumila West & G. S. West is the only known British species ; length of cells 5—6 ft; diam. 4-8— 5'7 p.; fig. 121 J. Family 3. BOTRYDIACEJE. This family is well marked off from the other groups of the Confer vales by the form of the plants alone. Each individual is a rounded coenocyte of macroscopic size and is attached to damp mud by well-developed ' rhizoids.' The chromatophores are very numerous and the methods of reproduction are somewhat diversified. Genus Botrydium Wallroth, 1815. The plants consist of green, pear-shaped or spherical coenocytes of considerable size, growing on damp mud into which they are rooted by a branched system of colourless rhizoids. The coenocytes are vesicular, with a lining layer of protoplasm in which are embedded numerous nuclei and chromatophores. The latter are irregular in form, more or less evenly scattered in one or more layers through the lining proto- plasm, and are generally in close contact with the nuclei. Bodies of the nature of pyrenoids have been observed in the younger stages of the plant, but starch is not formed. The rhizoids possess protoplasmic contents and many nuclei. Wager has observed mitotic division of the nuclei and states that the chromatic sub- stance appears to reside wholly in the nucleolus. This plant reproduces itself asexually in a great variety of ways, depending largely on the conditions .of environment, any Botrydiacece 259 j\A change of conditions usually resulting in a corresponding variation in the reproductive process. These different processes have been worked out by Rostafinski and Woronin1 and the final result is in each case either the production of zoogonidia or aplano- spores. The zoogonidia are small and ovoid in shape, with one or two chroraatophores and one long cilium. (Very pro- bably there is a second shorter cilium, but its presence has not yet been ascertained.) The whole plant frequently becomes a huge zoogonidangium, especially if it becomes submerged, and the zoo- gonidia escape through an apical opening. The aplanospores, which are globose or ellipsoid, often become hypnospores, and they are frequently produced in numbers in the rhizoids. On the green portion of the plant above ground becoming too dry, the contents migrate into the rhizoids and a large number of aplanospores are formed. The development of the young plants varies much, depending upon the external conditions. Rostafinski and Woronin described a sexual reproduction by the conjugation of isogamous gametes, but Klebs has given good reasons for doubting this. B. granulatum (L.) Grev. is a very local plant. It occurs widely distributed over the British Islands, but the conditions are not often suitable for its appearance above ground. It is found almost exclusively on drying-up mud, and sometimes occurs in countless numbers on mud turned out from a canal or on the drying bottom of a muddy pond. I have observed these plants so thick as to stand out in mulberry-like masses from the surface of the damp mud. The nature of the mud is immaterial and the Alga is not uncommonly found on chalk mud. The plants reach a diameter of 2'25 mm. Fig. 122. Fig. 122. Botrydium granulatum (L.) Grev., from Calverley, W. Yorks. A, nat. size; B and C, x45; D and E, x450; D, aplanospores; E, germinating aplanospore. 1 Rostafinski & Woronin in Botan. Zeitung, xxxv, 1877. 17—2 Class 5. BACILLARIE^:. THIS class of Algae includes a large number of minute plants known as the Diatoms. They are perhaps better known under the name of the Diatomaceae, but the earlier name ' Bacillariese ' has been in use for many years among systematists, particularly in continental Europe, and the name 'Diatomaceae' is here retained for one family only. The class is a very large one, with well- marked characters, and includes about 10,000 species. As would be expected among such a large number of species there is great variability of form, but at the same time the Diatoms always possess those salient features which mark them off from all other Algae. They are universally distributed in both fresh and salt water, and as the wonderful sculpture of their cell-walls renders them objects of great beauty, they have long been made the subject of special study by numerous students of natural history. Diatoms are unicellular plants, mostly of minute size, the cell- walls of which are composed of an organic matrix impregnated with silica. The silica can be removed by the action of hydro- fluoric acid, leaving the organic matrix behind ; or the organic matrix, which is allied in composition to cellulose, can be removed by calcination leaving behind the siliceous constituent. Each individual Diatom is termed a frustule, and the cell-wall consists of two more or less equal valves, joined together by two connecting -bands which overlap. Each half of the D.iatom is thus composed of two pieces, a valve and a connecting-band, and the connecting-band of the older half fits over that of the younger half like the lid of a cardboard-box. The connecting-bands, although closely fitted to their respective valves, are distinct from them, and the two bands together form what is termed the girdle. The latter does not usually consist of two closed hoops, but as Batittariece 261 Palmer and Keeley1 have pointed out, each band of the girdle is a two-ended band of silica with the ends overlapping without being joined. Each frustule possesses a thin coat of mucus which can be readily demonstrated by slight staining with aniline dyes. Diatoms often occur as solitary, free-floating individuals, but they may adhere to one another to form chains, either by their valve-faces to form ribbon-like or thread-like colonies (Eunotia, Melo- sira), or by mucous cushions at their angles to form zig-zag colonies (Tabellaria). Some adhere closely to larger plants by the whole of one valve-face (Cocconeis), or they are affixed to some larger object by simple or branched gelatinous stalks (Gomphonema); others occur in large colonies embedded in a common mucilaginous envelope, either as a compact mass or a simple or branch- ed tube. This condition is commoner in marine species than in freshwater ones, and is variable even in indi- vidual species. Marine Diatoms also reach a much larger size than freshwater ones. In referring to any individual Diatom, the aspect in which the girdle side is exposed to view is best termed the girdle-view (or zonal-view), and that in which the surface of the valve is exposed to view the valve-view. The valves are as a rule thin and transparent, slightly convex on the outside, and in almost all species they are ornamented with variously disposed striae. The best lenses, however, have shown that these striae consist of series of small cavities within the siliceous wall of the Diatom, and it is their close and regular arrangement that causes them to appear as striae. The striae are tv B Fig. 123. A, valve view of Navicula nobilis Ehrenb. var. Dac- tylus (Ehrenb.) V. H., from Dol- gelly, Wales (x250). B, girdle view of N. major Kiitz., from Shipley, W. Yorks. (x300). en, central nodule; iv, inner valve; ov, outer valve; pn, polar nodule; r, raphe. • 1 Palmer and Keeley in Proc. Acad. Nat. Sci. Philadelphia, 1900. 262 Bacillariece so extremely fine and constant in some species as to furnish splendid test-objects for the definition and angular aperture of the lenses of microscopes. The valves of some genera, particularly the marine ones, exhibit a beautiful areolated structure, due to the presence of chambers in the siliceous cell-wall. These chambers may be open to the exterior or covered by a thin membrane, and their inner walls are perforated by exceedingly minute apertures or pores which lead into the cell. . These pores are not present in all species of Diatoms, Miiller and Lauterborn having shown that in some species of Navicula (Pinnularia) they are probably absent. Schiitt affirms that there is no question of the existence of pores in many species of Diatoms, and their existence in a large number of others is extremely probable. He draws a distinction between pores and dots, and this has been further emphasized by Miiller. The latter1 has termed small circular dots which resemble pores 'poroids'; he gives O'l//. as the minimum diameter of pores, and 0'4 — 0*5 fj, as their maximum diameter, and all structures over 0'6/i he regards as ' poroids2.' Miiller3 recommends treatment with hot sodium carbonate and potassium hydrate in studying the structure of the cell-wall. Heribaud4 states that increased altitude and enfeebled light cause a diminution of the number of striae and of their strength, accompanied by an increase in the length and breadth of the valves. Many Diatoms exhibit a thickening of the cell-wall, visible in the valve-view, in the centre of the valve and very often at both extremities. These thickenings are known as nodules. The nodules are very frequently connected by a long median line known as the raphe. If the central nodule spreads out in a lateral direction it is known as a stauros. A portion of the valve on each side of the raphe and round the central nodule is often quite devoid of striae ; this plain or smooth portion of the valve is sometimes spoken of as a hyaline area. The raphe, for at least some part of its length, is a true cleft in the valve through which the protoplasmic contents of the cell are placed in communication with the surrounding medium. (Consult Fig. 124r.) 1 0. Miiller in Berichte Deutsch. Bot. Gesellsch. xvii, 1893. 2 O. Miiller, torn. cit. xviii, 1900. 3 0. Miiller, torn. cit. xix, 1901. 4 Heribaud in Comptes Bendus, cxviii, 1894. Bacillariece 263 Fig. 124. Transverse section of the frustule of a Navicula. (From Van Heurck, after W. Prinz.) cb and cb', the two connecting-bands forming the girdle; r, raphe; en, central nodule; c, costa of valve. (Very highly magni- fied.) Some Diatoms possess a pseudo-raphe, which is a simple line, central or sub-central, and without a central nodule. Often the raphe is conspicuous in both valves, but sometimes it is only present in one valve (Achnan- tties, Cocconeis, Rhoicosphenia). In many Diatoms the raphe is obscure and marginal or sub- marginal. In some species, such as Navicula nobil is Ehrenb., there is a smaller accessory raphe which lies alongside the primary one, and is united to it close to the central and terminal nodules. In Vanheurckia there is a sili- ceous rib on each side of the raphe and nodules, and in Am- phipleura the central nodule is greatly elongated. Some Diatoms (Fragilari- oideas, Mastogloia) possess longi- tudinal septa which are always more or less considerably perforated. These septa are parallel to the valve-faces and are usually situated between the girdle and the valves. Each individual Diatom contains a more or less centrally dis- posed nucleus, generally with a nucleolus. A very weak solution of methylene blue will bring out the nucleus in living Diatoms, staining it clearly before the rest of the protoplasm. The proto- plasmic mass surrounding the nucleus is connected with the primordial utricle either by two broad bands of protoplasm or by a number of radiating or anastomosing threads. One or several large vacnoles occupy the central portions of the cell. The chromatopkores of Diatoms are somewhat variable. One or many may be present in each cell ; they may be small and discoidal, large and plate-like, or extensive anastomosing masses occupying a large part of the lining protoplasm. In many species they are extremely irregular in form, being band-like, lobed, or even presenting the appearance of perforated plates. They are of a golden-yellow or brown colour, or very rarely green, as in some forms of Navicula viridis Kvitz. and N. cuspidata Kiitz. They contain chlorophyll, but this is masked by the presence of a brown 264 Bacillariece pigment known as diatomin, which resembles the phycophsein of the Phaeophyceae. The diatomin, which can be extracted by alcohol forming a yellow-brown solution, is itself a complex sub- stance containing, amongst other pigments, xanthophyll. An alcoholic solution of diatomin turns a beautiful blue-green colour on the addition of sulphuric acid. The chromatophores contain a variable number of pyrenoids which often project into the interior of the cell as rounded elevations. Mereschkowsky1 has observed pyrenoids which have partially or entirely emerged from the chromatophores, appearing as free colourless bodies on their inner surfaces. The nutrition of the vast majority of Diatoms is holophytic, but a few saprophytic forms are known'2. The latter are peculiar in the complete absence of pigment, and they apparently occur in water in which there is an abundance of decaying organic matter3. Karsten4 has found that Nitzschia palea (Kiitz.) W.Sm. when cultivated in favourable nutritive media will become saprophytic. Diatoms are incapable of growth in size owing to the siliceous nature of their cell-walls, but slight alterations of volume can take place by a sliding movement of the connecting-band of the older half of the cell over that of the younger half. In addition to the symmetrically arranged markings on the valves, the frustules of Diatoms possess an external symmetry in one or more planes. Some of them are zygomorphic in one plane only, some in three planes at right angles, and others exhibit a radial symmetry. The movements of Diatoms : — Most of the solitary, unattached species of Diatoms exhibit movements which have long been a puzzle to students of biology. This power of locomotion is especially marked in species of a naviculoid form, and various explanations have at different times been put forward to account for it. The movements of some forms are very slow, but others are capable of propelling themselves with considerable rapidity backwards and forwards in the direction of their longer axis. This spontaneous movement is sometimes creeping and steady, but at 1 Mereschkowsky in Flora, xcii, 1903, pp. 77 — 83. 2 The following are colourless saprophytic Diatoms : — Nitzschia putrida Benecke, N. leucosigma Benecke, and Synedra hyalina Provasck. 3 Benecke in Pringsheim's Jahrb. f. wissensch. Bot. xxxv, 1900. 4 Karsten in Flora, Ixxxix, 1901. Bacillariece 265 other times jerky, and is generally along a fixed substance with which the Diatom is in contact. It is not at all comparable to the free-swimming movements of many other Algae, and, as a rule, only takes place when one valve-face of the Diatom is in contact with the fixed object. Ehrenberg (1838) imagined the movement to be due to the protrusion of cilia or of a pseudopodium through the raphe of the valve, whereas Nageli (1849) attributed it to the passage of osmotic currents through the cell-wall. Max Schultze (1865)1, who observed the movements of minute foreign particles down the length of the raphe, attributed the locomotion to the contrac- tility of a small portion of the protoplasm which was protruded through the raphe. Hallier (1880) considered it to be due to a contractile layer of protoplasm, and Onderdonk (1885) also regarded it as due to an external movement of protoplasm, but Mereschkowsky (1880)2 concluded that the evidence was in favour of Nageli's theory of osmotic currents through the cell-wall. O. Miiller (1889)3 demonstrated the presence of a large number of minute pores and anastomosing fissures in the valves of certain of the large species of Navicula (Pinnuiaria), and showed that the central and terminal nodules are traversed by straight and curved canaliculi which run towards the raphe and are eventually merged with it. Owing to intracellular pressure the protoplasm emerges from the pores of 'the central or terminal nodules and passes down the whole length of the raphe, returning into the cell-cavity through the pores of the terminal or central nodules as the case may be. There are thus two sets of currents on each valve of the Diatom. The cause of the movement of the frustules was ascribed by Miiller to the reaction of the motive forces of this living stream of protoplasm upon the surrounding water. Schiberszky (1891)4, from observations on Synedra, agreed with Pfitzer that the move- ment was due to a coating of protoplasm which escapes from the raphe, and which is in a condition of vibratile motion. He believed that the currents along the raphe were usually interrupted jerking or pulsating movements. Cox (1890)5 revived the idea of a line of cilia along' the raphe, 1 Max Schultze in Archiv fiir Mikr. Anat. Bd i, 1865, p. 376. '2 Mereschkowsky in Bot. Zeitung, 1880, p. 529. 3 O. Muller in Berichte Deutsch. Bot. Gesellsch. Bd vii, 1889. 4 Schilberszky in Hedwigia, xxx, 1891. 5 J. D. Cox in The Microscope, July, 1890. 266 Bacillariece and suggested that the absence of silica along this line could be accounted for by the obstruction of the moving cilia. Biitschli (1892) also imagined that the presence of a cilium or a fine flagellum would explain the phenomenon, but no methods of staining have ever demonstrated the existence of such structures. The movements of some of the larger species of Navicula (Pinnularia) have been explained by Biitschli (1892)1 and by Lauterborn (1894)2 to be due to the production of a delicate filament which is protruded from the raphe at a point opposite the central nodule. The frustules of Navicula major Kiitz., N. nobilis Ehrenb., and N. viridis Ktitz. are surrounded by a distinct mucilaginous envelope, and the protruded filament is quite colourless and transparent, resisting all attempts to stain it with aniline dyes. It lies alongside the raphe, but not in contact with it, and it elongates by a series of jerks. Btitschli puts this forward as the explanation of the jerky movement of Diatoms, the frustule being pushed backward by the elongation of the filament, the distal end of which is fixed to the substratum. In 1893 0. Miiller3 again emphasized his previous explanation of the movements of Diatoms, affirming that they were dependent on the forces connected with the protoplasmic currents on the surface of the valve, and he denied that the movements could be the result of the filaments described by Biitschli and Lauterborn. He likewise stated that these filaments were composed of proto- plasm, and not of mucilage. Lauterborn (1894)4 contested that the production of motility by the streaming of protoplasmic currents, as suggested by Miiller, would be an isolated phenomenon in either the vegetable or animal kingdom, whereas movements are known to occur in the Desmidiaceae and Oscillatoriaceae as a result of the excretion of mucilage, and, according to Schewiakoff, in the creeping Gregarinidse also. Miiller (1894)5 replied again to the criticism of his hypothesis, and stated that the analogy which had been drawn between the movements of Diatoms and of Desmids was a false one. There is no doubt that in many of the smaller motile species there is a complete absence of gelatinous filaments such as those 1 Biitschli in Abhandl. naturh.-med. Ver. Heidelberg, 1892, Bd iv, Heft 5. 2 Lauterborn in Berichte Deutsch. Bot. Gesellsch. Bd xii, 1894, p. 73. 3 O. Miiller in Berichte Deutsch. Bot. Gesellsch. Bd xi, 1893. 4 Lauterborn, torn. cit. xii, 1894. 5 0. Miiller, torn. cit. xii, 1894. Bacillariece 267 occurring in the larger species of Navicula (Pinnularia), even though the movements of the frustules, the structure of the valves, the system of fissures and pores, and the arrangements of the protoplasmic currents are the same. In some of the small species of Navicula the movements are extremely active, comparing not unfavourably with the slow movements of certain of the Infusoria. If the movements of such Diatoms be due to the secretion of gelatinous material, then the amount secreted in a short space of time must be relatively enormous. After a careful consideration of the facts which have been brought forward with a view to the elucidation of this most interesting problem, there appears to be no doubt that the move- ments are connected with the raphe, and the balance of evidence indicates that in some Diatoms at least they are due to an exuda- tion of mucilage. The multiplication of Diatoms takes place by successive bipartitions, each division resulting in a gradual reduction in the size of the individuals. A slight increase in the volume of the frustule is the first appreciable change, after which the nucleus divides karyokinetically. A division of the cell-protoplasm now takes place, and a new siliceous valve is formed over each divided surface. These new valves are situated within the girdle of the original frustule, and the connecting-bands of the new valves are soon developed, sometimes making their appearance before and sometimes after the separation of the individuals. Thus, each individual consists of a new valve and an old one, the connecting- band of the old valve overlapping that of the new valve. Some- times the cells do not separate, but remain in contact after division, successive bipartitions resulting in a chain of individuals. Owing to the formation of a pair of new valves within the girdle of the old ones, and since the cells when once formed are incapable of growth, every succeeding generation becomes reduced in size by the double thickness of a connecting-band. This statement is not strictly true, however, in the case of some of the filamentous species, and possibly in many others. It has been shown that daughter-cells are often produced of larger size than the parent- cells, such daughter-cells being recognizable by the thickened rim of the" valves. This fact has a retarding influence on the diminu- tion o'f the size of the cells, the reduction in size not being in strict proportion to the number of bipartitions ; and, concerning 268 Bacillariece the multiplication in the filamentous genus Melosira, Miiller1 has drawn up a definite law of division. He has shown that the multiplication of the cells takes place in such a manner as to prevent as much as possible the division of the smallest daughter-cells. This law, although indicating the prevailing conditions of multiplication in Melosira, is not true of all Diatoms. On the greatest diminution of size having been reached for any one species, the maximum size of the species is regained by the formation of an auxospore, and there are five methods of reproduction by auxospores. (1) The protoplasm of a cell of the smallest size (sometimes termed a ' microfrustule ') swells up and forces apart the halves of the frustule, escaping to the exterior enveloped in a cellulose membrane. This is the auxospore, the wall of which rapidly becomes silicified and assumes the markings characteristic of the species, but the form of the cell is usually very different from that of the original frustule, and often most irregular. This large, newly-formed cell of irregular appearance almost immediately undergoes division, the individuals of each succeeding generation rapidly regaining their characteristic form and elegance. Miquel2, who has made a special study of the manner in which the maximum form of a Diatom is re-established, based upon experimental cultures of a number of species, states that such re-establishment of the maximum size is habitually brought about by the formation of this simple type of auxospore. It is merely the rejuvenescence of a single cell accompanied by an increase in size. (Fig. 125 C and D.) (2) Two auxospores may be produced by the division of the contents of a single frustule. Each of the two portions of the cell-contents emerges from the cell and develops as in the first method. This method has only been observed in Rhabdonema arcuatum (Ag.) Kiitz. and Achnanthes longipes C. Ag. (3) An auxospore may be formed by the conjugation of the contents of two frustules. The two Diatoms become enveloped in a common mucous covering, and the cell-contents emerge and fuse to form a single body, which then develops into an auxospore. 1 Miiller, ' Die Zellhaut und die Gesetze der Zelltheilungsfolge von Melosira arenaria Moore.' Berlin, 1883. 2 Miquel in Annal. de Micrographie, iv, 1892. Bacillariece 269 This is a true conjugation of aplanogametes with the formation of a zygospore. (Fig. 125 B.) (4) Sometimes two frustules approximate and the cell-contents throw off the old valves, but there is no conjugation. The two rounded masses of cell-contents lie close together or separated by some of the enveloping jelly, and each develops "independently into an auxospore. (5) A pair of Diatoms ap- proximate, but before conjugation the protoplasm of each cell divides into two daughter-cells. Two auxospores are then formed by the fusion of a daughter-cell from each mother-cell with a daughter- cell from the opposite mother- cell. This is known to occur in Amphora ovalis Kiitz., Epithemia Argus (Ehrenb.) Kiitz.1, and Na- vicula limosa Kiitz. (Fig. 125 A.) A normal auxospore can be regarded as one produced by the conjugation of two cells (or ga- metes), those produced without conjugation being parthenoge- netic. The first and the fourth methods are the ones most fre- quently observed. The most im- portant feature in the formation of an auxospore is the increase in size of the cell. Karsten2 considers that the majority of Diatoms exhibit undoubted sexuality. Castracane and other observers have recorded another method of reproduction by the formation of small spores within the frustules. Kitton3 and Lock wood4 have each stated that Diatoms may possess spores (" microspores ") so small as to pass through 1 Klebahn in Jahrb. fur wissensch. Bot. xxix, 1896. - Karsten in Biol. Centralbl. xx, 1900 ; Flora, Ixxvii, 1900. 3 Kitton in Journ. Quekett Micr. Club, ser. 2, ii, 1885, p. 178. 4 Lockwood in Journ. New York Micr. Soc. 1886, ii, p. 153; Fig. 125. A, Navicula limosa Kiitz., from the New Forest, Hants. ( x 450). B,Achnanthesflexella (Kiitz.) Breb. , from Craig-an-Lochan, Scot- land (x450). C, Navicula Amphis- b_ 15J- Ammatoidea Normanii J . . . W. & G. S. West, from Dartmoor, chomes exhibit a slight constric- Devonshire ( x 420). 342 Myxophycece tion between their median cells, and the apical cells are about six times longer than their diameter. A. Normanii W. & G. S. West is known from Devonshire as an epiphyte on Batrachospermum moniliforme. Thickness of filaments 5'5 — 12'5 ^ of trichomes 3'5 — 5 '5 p. ; fig. 158. Order II. COCCOGONE^. In this order the plants are unicellular or colonial, commonly occurring as colonies of unicells enveloped in a copious gelatinous investment. The colonies vary much in size and shape, being spherical, ellipsoidal, or expanded gelatinous masses. The cells are of varied form and are disposed in a variety of ways within the mucous envelope. The latter is sometimes conspicuously lamellose, but more often it is hyaline and structureless. The Coccogoneae constitute the lowest group of the Myxophycese, and indeed they are the most primitive of all the Algae. They occur free-floating, or more rarely as epiphytes, and some' of them form gelatinous masses on wet rocks. Not a few are regular and abundant constituents of the freshwater plankton. The normal method of multiplication is by simple cell-fission, the larger colonies ultimately breaking up to form smaller ones. Sometimes young colonies arise at the sides of the older ones by a process of budding. Rounded asexual spores or gonidia have been observed in some species, being formed within the wall of a mother-cell. Zoogonidia are unknown. There are two well-marked families. Family 1. Chamcesiphoniacece. Cells epiphytic, with a distinct base and apex ; reproduction only by the formation of gonidia. Family 2. Ckroococcacece. Cells or colonies free-floating or form- ing a gelatinous stratum, very rarely epiphytic, not differentiated into base and apex ; multiplication by simple cell-division (very rarely by gonidia). Family 1. CHAMJESIPHONIACE^l. The plants of this family are epiphytes, generally occurring in clusters around the filaments of larger Algae. They are in all cases differentiated so as to present a distinction between base and apex, and reproduction occurs by the formation of a number Chroococcacece 343 of non-motile spores or gonidia from the contents of a mother-cell. Most Algge of this family are marine, the only British freshwater genus being Chamcesiphon. Genus Chamaesiphon A. Br. & Grun., 1864. [Indus. Sphcero- gonium Rostaf., 1883.] The cells are small, ovoidal, pyriform, or cylindrical, with very thin cell-walls. The cell-contents are homo- geneous and of a blue-green, violet, or yellow colour. The cells are attached by their base and generally widen upwards to their free apex. The gonidia are successively cut off from the upper part of the cell which has become a gonidangium, gradually escaping from the open apex. Fig. 159. Chamcesiphon incrustans Grun., on a filament of Rhizoclonium, from Heaton, W. Yorks. ( x 416). Ch. confervicola A. Br. is found as an epiphyte on Chcetomorpha, Rhizoclo- nium, Vaucheria, etc., and Ch. incrustans Grun. (diam. of cells 3'5 — fig. 159) often thickly covers filaments of Rhizoclonium and (Edogonium. Family 2. CHROOCOCCACEJE. This is the largest family of the Coccogoneae, and includes a great variety of unicellular and colonial blue-green Algae. They are abundant in all kinds of damp and wet situations, frequently forming a gelatinous stratum on the damp surfaces of dripping rocks. The cells vary much in shape in the different genera, and the colonies assume different forms according to the direction of division of the cells. In some the cells divide in every direction of space within a gelatinous envelope, producing an irregular colony, often of large size. In others the cells divide only in two directions in the same plane, giving rise to a tabular colony ; and in others cell-division takes place in one direction only. In one genus (Tetrapedia) the cells are flattened and they possess a striking symmetry of form. Synechococcus and Tetrapedia are the only genera which are commonly destitute of a mucous envelope. In all others the cells are invariably embedded in a mass of mucus, 344 Myxophycece which varies much in its consistency. It may be firm and lamellose, or very hyaline and diffluent. The cells often contain red, orange, or violet pigments. Reproduction has been observed in a few species to take place by the formation of non-motile spores or gonidia within a goni- dangium. There are two sub-families : — Sub-family I. Chroocystece. Epiphytes on larger Algae, with a well-defined dorsiventrality. Sub-family II. Chroococcece. Free-floating or forming a gelatinous stratum, with no dorsiventrality. Sub-family I. CHROOCYSTE^. This sub-family includes only a single genus, the plants of which .differ from the rest of the Chroococcacese in being epiphytic, and in the possession of distinct upper and lower surfaces. They are likewise characterized by the possession of prominent bristles. Genus Gloeochsete Lagerh., 1883. [Schrammia Dangeard, 1889.] The cells are globose or sub-globose, enveloped in a wide Fig. 160. Glceochcete Wittrockiana Lagerh. A, from Cray Moss, W. Yorks. ; B, from Pilmoor, N. Yorks. ( x 416). mucous coat, and they occur singly, or in twos or fours, attached to larger filamentous Algae. More rarely they are attached to the Chroococcacece 345 leaves and stems of submerged Mosses or Phanerogams. Each cell is furnished at its upper pole with one or two long, thin bristles, which sometimes give off small branches or spurs near their apices. The primitive chromatophore is bell-shaped, of a brilliant blue-green colour, and there is a clear space in the centre of the cell. Lagerheim in his original description of the genus1 says " nucleus singulus." The mother-cells give rise to two or four daughter-cells on division. Many authors have placed this Alga in the Chlorophyceae, or have recorded a chlorophyceous Alga under the name of ' Gloeochcete,' The genus as I have often found it, and as here figured, most certainly belongs to the Chroococcaceae. Gl. WittrocJciana Lagerh. is known from several parts of the British Islands, occurring as an epiphyte on Vaucheria, Cladophora, or the leaves of Sphagnum. Diam. of cells 6—21 p ; length of bristles 96—260 p ; fig. 160. Gl. bicornis Kirchn. has a pair of bristles attached to each cell. Sub-family II. CHROOCOCCE^. The sub-family Chroococceae embraces almost all the unicellular and colonial Myxophyceae. They are unquestionably of a lower type than any other of the Algse, and some of them bear resemblance to certain of the Bacteria. The cells display considerable variety of form, and with the exception of the genera Synechococcus, Tetrapedia, and to a certain extent Merismopedia, they are enveloped in a copious covering of mucus. The mucous coat is sometimes firm and lamellose, as in some species of Chroococcus and Glceocapsa, but more often it is an ample, homogeneous covering, very hyaline in character. It often happens that the coverings of numerous cells have fused together, thus forming gelatinous colonies of various sizes. Some of these colonies are large macro- scopic masses, containing many thousands of cells, and possessing a tough exterior. In some genera, such as Merismopedia and Ccelospkcerium, the colonies are of limited size and of definite shape. Multiplication takes place by the repeated division of the cells and the final fragmentation of the original colony, each fragment growing in size and repeating the processes. In the spherical colonies of Ccelosphcerium a kind of budding takes place by means 1 Lagerheim in Nuova Notarisia, 1890, p. 231. 346 Myxophycece of which a new colony is developed from the side of the old one, ultimately becoming separated from it. Cell-division may be in one direction only, in two directions in one plane, or in every direction of space. Reproduction occurs in Gomphosphceria by non-motile spores or gonidia1. There are thirteen British freshwater genera, which can be arranged as follows :— A. Cell-division in one direction only. * Cell-division transverse. t Cells enveloped in a wide mucous coat. J Cells elongated, each with a mucous coat Glceothece. |J Cells little longer than broad, enveloped in a common mucous investment . . . Aphanothece. tt Cells destitute of mucus Synechococcus. ** Cell-division oblique ; cells enveloped in mucus Dactylococcopsis. B. Cell-division in two directions in one plane. * Cells globular or rounded-quadrate ; colonies often large Merismopedia. ** Cells of a definite symmetrical form, solitary, or forming small colonies Tetrapedia. C. Cell-division in all directions of space ; cells enveloped in mucus. * Cells forming large colonies. t Cells arranged at or towards the periphery of spherical colonies. | Cells closely and regularly arranged . . . Ccelosphcerium. H Cells geminate and sparsely scattered, markedly py riform in shape Gomphosphceria. tt Cells densely aggregated in globose, elon- gated, or clathrate colonies Microcystis. +tt Cells aggregated to form irregular gelatinous colonies. J Individual mucous coats clearly evident round each cell Gloeocapsa. J| Cells enveloped in a common mucous covering Aphanocapsa. \\\ Cells arranged in a compact gelatinous stratum Porphyridium. ** Cells more or less solitary, or forming very small colonies Chroococcus. Genus Gloeothece Nag., 1849. The cells are cylindrical and elongated, each one being surrounded by a thick mucous coat, which sometimes shows indications of lamellation. Cell-division 1 Schmidle in Berichte Deutsch. Botan. Gesellsch. 1901, xix. Chroococcacece 347 is only in one direction, and a number of cells are usually associ- ated to form a small colony. Species of this genus occur on wet rocks, among wet mosses, and in bog- pools. Gl, linearis Nag. (length of cells 1O5 — 18 p; breadth 1'3 — 2'3/ij fig. 161 A) and Gl. confluens Nag. (length of cells 57 — 7'5 p. ; breadth 2'6— 3 p ; fig. 161 B) are the most frequent British species. Rhabdoderma linear e Schmidle1 seems very closely allied to Glceothece linearis Nag., if not actually identical with it. Genus Aphanothece Nag., 1849. This genus only differs from Glceothece in the ag- gregation of large numbers of cells within a common mass of mucus. The cells are cylindrical and longer than their diameter. A. microscopica Nag. (length of cells 5—8 p, breadth 3'5— 4 p ; fig. 161 C) and A. saxicola Nag. are the most frequent species. They are found in bog-pools, at the margins of lakes, and on wet rocks. Genus Synechococcus Nag., 1849. The cells, which are cylindrical with hemispherical apices, are larger than in the preced- ing genera, and are desti- tute of the outer mucous coat. They occur free- floating in ponds, ditches, and bog-pools, often in considerable quantity. The cell-contents are usually of a brilliant blue-green, rarely of a rose-purple colour, and contain numerous large granules. S. ceruginosus Nag. and S. major Schroeter (length of cells 26 — 29 p; breadth 15'5 — 17'5 p ; fig. 161 D and E) are the most abundant British species, the latter often occurring in quantity in bogs. Genus Dactylococcopsis Hansg., 1888. The cells are generally associated to form small colonies, rarely solitary, and in many 1 Schmidle in Berichte Deutsch. Botan. Gesellsch. 1900, xviii, p. 149, t. vi, f. 8—11. Fig. 161. A, Glceothece linearis Nag., from Old Cote Moor, W. Yorks. B, Gl. confluens Nag., from near Settle, W. Yorks. C, Aphano- thece microscopica Nag., from Withiel, Corn- wall. D and E, Synechococcus major Schroet., from Adel Bog, W. Yorks. (All x 450.) 348 cases the colonies are embedded in a copious mucus. The cells are elongated, fusiform or lanceolate, with attenuated extremities, or sometimes sigmoidal in form. The chromatophore is almost homogeneous, of a pale blue-green colour, and somewhat lateral in position. Division of the cells occurs much as in Dactylococcus, by oblique septation. D. montana W. & G. S. West (length of cells 8'6— 11 '5 p., breadth 3'5— 4 p ; fig. 162 A) occurs in bog-pools amongst Sphagnum. D. rhaphidioides Hansg. is known from the plankton of Lough Neagh. Genus Merismopedia Meyen, 1839. This is one of the most striking genera of the Chroococcacese, consist- ing of a flat rectangular colony, the cells of which are arranged in rectilinear series. Cell-division takes place in two directions and the cells appear to be usually arranged in groups of four. The cells are globose, ellipsoidal, or oblong, sometimes slightly angular by compression, and the cell-contents are homogeneous. Fig. 162. A, Dactylococcopsis montana W. & G. S. West, from Widdale Fell, W. Yorks. B, Merismopedia glauca (Ehrenb.) Nag., from Thursley Common, Surrey. C, M, elegans A. Br., part of a large colony from Wicken Fen, Cambridge. D, Tetrapedia Reinschiana Arch., from near Goring, Oxford. (All x 450.) M. glauca (Ehrenb.) Nag. is the commonest British species, occurring in ponds, ditches, bogs and lakes; diam. of cells 3'3 — 3'8/n; fig. 162 B. M. punctata Meyen and M. ceruginea Breb. are not infrequent in stagnant water. M, elegans A. Br. is the largest species of the genus and is known from few localities in the British Islands; diam. of cells 6'5 — 9-5 p.; fig. 162 C. The colonies of M. gloMca and M. elegans often reach a large size (diam. up to 220 /i) and may contain as many as 1856 cells. Genus Tetrapedia Reinsch, 1867. In this genus the cells are of some definite and symmetrical shape, often constricted into two equal half-cells. The cell-wall is firm and the cell-contents are homogeneous. In some species the cells are almost invariably solitary, but in others they are grouped in flat colonies similar to those of Merismopedia. Chroococcacece 349 All the species are rare, but T. Reinschiana Arch. (diam. of cells 5'5 — 6 /i ; fig. 162 D) and T. glaucescens (Wittr.) Boldt occur in lakes and bog-pools. T. setigera Arch, is a beautiful little species known from N. W. Scotland and W. Ireland, and which has been erroneously referred by some authors to the chlorophyceous genus Tetraedron. The cell-contents of Tetrapedia setigera are homogeneous and of a pale blue-green colour. Genus Coelosphserium Nag., 1849. The cells are more or less closely grouped to form a hollow, spherical colony. They are em- bedded in a mass of mucus and are arranged just within the periphery of the spherical mass. In form they are globose, ellip- soidal, or ovoidal, and the cell-contents are granular, with so-called gas-vacuoles. The genus is a common constituent of the freshwater plankton, and is also found frequently in large ponds. C. Kiitzingianum Nag. (diam. of colony 48 — 90 p. ; diam. of cells 3 — 3'8 p ; fig. 163 A) is the most abundant species, although C. Niigelianum Unger and C. minutissimum Lemm. both occur in quantity in the British freshwater plankton. Fig. 163. A, Ccelosphcerium Kiitzingianum Nag., from the plankton of Lough Neagh, Ireland. B, Gomphospharia aponina Kiitz., from Keston Common, Kent (x350). Genus Gomphosphseria Kiitz., 1836. In this genus the colonies contain fewer and more scattered cells, which are disposed chiefly towards the periphery of a globular or ellipsoid mass of mucus. The cells are grouped in pairs and are distinctly pyriform in shape. Schmidle has observed the formation of ' microgonidia.' The entire colony is solid and the cells divide alternately in three directions. G. aponina Kiitz. (diam. of colonies 64 — 78 /*; length of cells 8'5 — 11'5/x; fig. 163 B) is not uncommon in ponds, lakes, and stagnant ditches. Genus Microcystis Kiitz., 1833. [Polycystis Kiitz., 1845 ; Clathrocystis Henfrey, 1856.] The cells are small, mostly globose, 350 Myxophycece and are densely aggregated to form solid colonies of variable shape. In some species the colonies are globose, ellipsoidal, or oblong ; in others they are much elongated ; and in others they become ela- thrate and almost anasto- mosing. The cell-contents are blue-green, olive-green, or rose-purple in colour, and often contain gas- B vacuoles. Fig. 164. A, Microcystis stagnalis Lemm., M. marginata Menegh. from the plankton of Lough Neagh Ireland. (diftm< of cells 2-6— 2'8/i; fig. B, M. marginata Menegh., from Old Cote Moor, W. Yorks. ( x 450). 164 B)> M- flos-aquce (Wittr.) Kirchn., N. elabens (Breb.) Kiitz., and M. stagnalis Lemm. (diam. of cells 1 — 1'5 p. ; fig. 164 A) are all more or less common in bogs and lakes. M. roseo-persicinus (Kiitz.) often occurs in quantity in ponds and ditches which contain much decaying vegetation. M. ceruginosa (Kiitz.) [ = Clathrocystis ceruginosa (Kiitz.) Henfrey] often occurs in prodigious quantity in ponds and in the plankton of lakes. The three genera Microcystis, Polycystis and Clathrocystis are not suffi- ciently distinct to warrant their separation. The differences between them are only differences of degree. Genus Gloeocapsa Ktitz., 1843 ; em. Nag. 1849. The cells are globose and furnished with a thick integument, which is frequently lamellose. The daughter-cells which arise by the division of the mother-cells are generally retained as part of the colony, a larger integument surrounding the individual envelopes of the cells. In this manner the colonies become of large size and frequently form a gelatinous stratum. The integuments of the cells are sometimes colourless, but they may be yellow, brown, blue, violet, or red. Cell-division takes place in all directions and the colonies are most irregular. Thick-walled resting-spores have been observed in some species. Kuntze and, following him, certain other authors, have identi- fied Gloeocapsa Kiitz. with Bichatia Turp. (1827), but to my mind this identification is uncertain. There are about 20 British species, some of which are of doubtful specific distinctness. Gl. punctata Nag. (diam. of cells 1'5 — 2/x) is the smallest species. Gl. polydermatica Kiitz. is remarkable for the larnellatiou of the integuments (fig. 165 C — E). Gl. Magma (Breb.) Kiitz. with golden-yellow or Chroococcacece 351 brown integuments (fig. 165 B), and Gl. Ralfsiana (Hass.) Kiitz. with bright red or purple integuments, are two of the best-defined species. Most of the species occur on wet or dripping rocks, generally in association with other Myxophycese. J» Genus Aphanocapsa Nag., 1849. aggregated to form small colonies within a com- mon homogeneous in- tegument. The genus only differs from Apha- nothece in its globose cells. The integument may be colourless or tinted brown or blue- green, and the cells are of a blue-green or olive- green colour. There are four British species occurring both in stagnant water and on wet rocks. A. Grevillei (Hass.) Rabenh. is the most fre- quent ; diam. of cells 3'4 — 4-5 p; fig. 165 A. The cells are globose and C D Fig. 165. A, Aphanocapsa Grevillei (Hass.) Eabenh., from Helln Pot, W. Yorks. B, Glceo- capsa Magma (Breb.) Kiitz., from Boston Spa, W. Yorks. C — E, Gl. polydermatica Kiitz., from Boston Spa, W. Yorks. (All x 450.) Genus Porphyri- dium Nag, 1849. The cells, which are closely arranged to form a thin gelatinous stratum, are globose or angular by compression. The stratum consists of many layers of cells, and the cell-contents are of a reddish-purple colour. Cell-division takes place in all directions. P. cruentum (Ag.) Nag. is a common Alga, forming a thin slimy stratum of a dark red colour on damp ground and near the base of damp walls. The cells are 7 — 9 /A in diameter. This Alga was at one time placed in the Chlorophycese and has since been relegated to the Rhodophyceae. I agree with Hansgirg, however, in thinking it much better placed in the Myxophycese. There are many of the Myxo- phyceae which possess as much red or purple pigment as Porphyridium, and moreover, the latter genus is generally found in association with blue-green Algae. It is more nearly allied to Aphanocapsa than any other genus of 352 Myxophyceaz Genus Chroococcus Nag., 1849. In this genus the cells are globose or more or less angular, solitary or associated in simple families. They are free- floating or mixed with other blue-green Algae to form a stratum on wet rocks. The integuments are firm and often wide, homogeneous or lamel- lose, generally colourless, but sometimesof a yellow- ish-brown tint. The cell- contents are granulose, of a brilliant blue-green colour, or more rarely violet, olive-green, or yellow-green. Fig. 166. A, Chroococcus giganteus West, from Bowness, Westmoreland. B, Ch. turgidus (Kiitz.) Nag., from Slieve Donard, Down, Ireland. C and D, Ch. schizodermaticus West, from near Windermere, Westmoreland. (All x 450.) Ch. turgidus (Kiitz.) Nag. is the most widely distributed species, often occurring in quantity in Sphagnum-bogs ; diam. of cells 13 — 25 p.; fig. 166 B. Ch. cohcerens (Breb.) Nag., Ch. giganteus West (fig. 166 A), Ch. minor (Kiitz.) Nag. and Ch. pallidus Nag. are not infrequent in ponds, lakes, and bog-pools. Ch. schizodermaticus West (fig. 166 C and D) is remarkable for its tough lamellose integuments, the layers of which are gradually split off and shed. Ch. lim- neticus Lemm. is confined to the freshwater plankton. INDEX. [Synonyms are printed in italics, and the numbers in strong type refer to the descriptions of the genera, families, orders, etc.] Acanthococcus Lagerh., 203. Achnanthacese, 289, 290. Achnanthes Bory, 263, 289. coarctata Breb., 290. exilis Kiitz., 290. flexella (Kiltz.) Breb., 269 (fig. 125 B), 290. Hungarica Grun., 290 (fig. 135 A— C). linearis W. Sm., 290. longipes C. Ag., 268. microcephala Kiltz., 290. Achnanthidium Kiitz. (sect, of Achnan- thes), 289, 290. Achnanthoideas, 280, 289—291. Actinastrum Lagerh., 218, 224. Hantzschii Lagerh., 225. Ajuga, 199. Akinetes, 15. Akontce, 32. Alocasia, 55. Alternation of generations, 18. Amblystegium exannulatum, 4. falcatum, 4. glaucum, 4. scorpioides, 4. Ammatoidea W. & G. S. West, 38, 337, 341. Normanii W. & G. S. West, 341 (fig. 158), 342. Amoeba, 4, 145, 230. Amphicampa Ehrenb. (1849), 288. Amphicampa Kabenh. (1864), 296. Amphipleura Kiitz., 263, 292, 295. pellucida Kiitz., 295 (fig. 137 C). Amphiprora Ehrenb., 291, 292, 296. ornata Bail., 296. paludosa W. Sm., 296 (fig. 138 B and C). Amphithrix Kiitz., 338. janthina (Mont.) Born. &Flah.,338. W. A. Amphora Ehrenb., 298, 299. ovalis Kiitz., 269, 299 (fig. 141 B and C), 300. ovalis var. pediculus Kiitz., 300. Anabana Bory., 311, 312, 314, 317, 325, 327. circinalis Rabenh., 328. Flos-aquas Breb., 328. intequalis (Kiitz.) Born. <£ Flah., 328 (fig. 150 A— D). oscillarioides Bory, 328. Ancylonema Berggr., 144, 149. Nordenskioldii Berggr., 5, 51. Androgonidia, 191. Androsporangium, 61. Androspore, 61. Ankistrodesmus Corda, 159, 218, 221, 222—225. acutissimus Arch., 222, 223. biplex (Reinsch) nob., 224. convolntus (Rabenh.) nob., 224. falcatus (Corda) Ralfs, 53, 223 (fig. 94 A), falcatus var. acicularis (A. Br.) nob., 223 (fig. 94 B and C). falcatus var. duplex (Kiitz.) nob., 223. falcatus var. mirabilis nob., 223 (fig. 94 E), 224. falcatus var. spiralis (Turn.) nob., 224. falcatus var. spirilliformis nob., 224. falcatus var. tumidus nob., 223 (fig. 94 D), 224. fusiformis Corda, 222, 223. Pfitzeri (Schroder) nob., 223 (tig. 94 G and H), 224. setigerus (Schroder) nob., 223 (fig. 94 F), 224. Anodonta, 4. Anorthoneis Grun., 290. 23 354 Index Antheridium, 17. Antherozoids (or spermatozoids), 17. Anthoceros, 325. Aphanizomenon Morren, 308, 311, 326, 328. Flos-aquae (L.) Ealfs, 328. Aphanocapsa Nag., 346, 351. Grevillei (Hass.) Rabenh., 351 (fig. 165 A). Aphanochcete A. Br. ; Berth. ; Huber, 71, 72, 89, 182. globosa var. minor Hansg. , 182. pilosissima Schmidle, 72. repens A. Br., 72. Aphanothece Nag., 13, 346, 347, 351. microscopica Nag., 347 (tig. 161 C). saxicola Nag., 347. Apiocystis Nag., 51, 239, 244. Brauniana Nag., 244 (fig. 112). Aplanogametes, 16. Aplanospores, 15. Aptogonum Ealfs, 177. Archegoniatae, 30. Archer, 1, 141, 142, 223. Archiplast, 317. Archiplastidese, 309, 316, 317—352. Areschoug, 75. Arisarum, 55. vulgare, 54. Arthrodesmus Ehrenb., 137, 144, 151, 169, 170. bifidus Breb. var* truncatus West, 170 (fig. 64 H— J). convergens Ehrenb., 171. Incus (Breb.) Hass., 170 (fig. 64 A— C), 171. Incus var. Ealfsii W. <& G. S. West, 170 (fig. 64 D). Incus var. validus W. & G. S. West, 170 (fig. 64 E). octocornis Ehrenb., 170 (fig. 64 F and G), 171. Arthrodia Kafiuesque, 159. Arthrodieas, 148. Arthrosiphon Kiitz., 323. Arthrospira Stizenb., 315, 330, 332, 333, 336. Jenneri (Hass.) Stizenb., 336. Asexual reproduction, 14, 15. Askenasy, 210. Asterionella Hass., 287. formosa Hass., 287 (fig. 133). gracillima Heib., 287. Autocolony, 25, 212. Autospores, 14, 25, 212. Auxospores, 268, 269. Azolla, 4, 325. Bacillaria Gmelin, 301, 302. paradoxa Gmelin, 302. Bacillarieffi, 5, 6, 8, 11, 15, 16, 31, 32, 260—305. Bacteria, 3, 316, 332, 345. Bangia, 36. Bangiaceae, 35, 98. Batrachospermum Roth, 18, 20, 36, 38, 39, 339. atrum (Dillw.) Harv., 38. Boryanum, 35. moniliforme Roth, 37 (fig. 1 A), 38, 342. vagum (Roth) Ag., 37 (fig. 1 B and C), 38. Benecke, 264. Bennett, 1. Bennett & Murray, 111, 125. Berggren, 5. Bessey, 148. Beyerinck, 230. Bichatia Turp. , 350. Biddulphoideae, 273. Binuclearia Wittr., 75, 80. tatrana Wittr., 80 (fig. 25), 81. Blackman, 2, 21, 22, 24, 27. Blackman & Tansley, 32, 33, 102, 188, 248. Blasia, 4. Boergesen, 1, 99, 143. Bohlin, 21, 26—29, 32, 100, 108, 248,' 253, 254, 256. Boldt, 143. Borge, 1, 12, 125, 147. Bornet, 1. Borzi, 2, 21, 28, 48, 78, 92, 182, 199, 248, 311, 314, 326, 339. Botrydiacese, 29, 30, 249, 258, 259. Botrydina Breb., 247. vulgaris Breb., 247. Botrydiopsis Borzi, 28, 29, 254. Botrydium Wall., 12, 18, 28, 29, 51, 258. granulatum(L.) Grev., 259 (fig. 122). Botryococcus Kiitz., 235, 237. Braunii Kiitz., 237 (fig. 106), 242. calcareus West, 237. sudeticus Lemm., 237, 242. Boubier, 114. Bradypus (Three-toed Sloth), 55. Brand, 93, 104, 106. Brandt, 5, 311—313. Breaking pf the Meres, 315, 341. Brewer, 6, 307. Bulbochsete Ag., 52, 57, 58, 65. gigantea Pringsh., 65. nana Wittr., 64 (fig. 15 C), 65. Nordstedtii Wittr., 64 (fig. 15 B). subintermedia Elfv., 64 (fig. 15 A). Bumilleria Borzi, 29,' 253, 258. pumila W. & G. S. West, 257 (fig. 121 J), 258. Biitschli, 266. 355 Callitriche, 205. Catocylindrus (Nag.) Kirchn., 166, 167. Calothrix Ag., 38, 312, 338. epiphytica W. & G. S. West, 339. fusca (Kiitz.) Born. & Flah., 339. parietina (Nag.) Thur., 339 (fig. 156 A and B). Campbell, 21. Camptothrix W. & G. S. West, 341. Camptotriehaceffi, 337, 341, 342. Campylodiscus Ehrenb., 303, 305. Echineis Ehrenb., 305. Hibernicus Ehrenb., 305 (fig. 145 D and E). Capsulococcus Bennett, 246. crateriformis Bennett, 246. Carotin, 308. Carpogamous heterogamy, 16. Carpogonium, 16, 17, 34. Carpospores, 16. Carteria Dieting, 187. multifilis (Fresen.) Dill, 187, 188 (fig. 73 A— G). Castracane, 269, 270, 272. Caulerpa, 25, 109. Cellulose, 51. Central body (of Myxophyceae), 309, 310. Centricse, 273 — 279. Centrosphaera Borzi, 199. Faeciolase Borzi, 198 (fig. 79 B and D), 199. Cephaleuros, 4, 13. Cerasterias Reinsch, 231. longispina (Perty) W. <& G. S. West, 232. rhaphidioides Reinsch, 232. Ceratodus, 7. Ceratoueis Ehrenb., 288. Arcus (Ehrenb.) Kiitz., 288 (fig. 134 D). Arcus var. Amphioxys (Rabenh.). I)e Toni, 288. Cercidium elongatum Dang., 189. Chaatomorpha Kiitz., 102, 103, 343. sutoria (Berk.) Rabenh., 103 (fig. 38). Chaetonella Schmidle, 106. Goetzei Schmidle, 106. Chsetopeltis Berth., 180, 181. orbicularis Berth., 181. Chaetopeltideas, 30, 52, 179, 180—184. Chsetophora Schrank., 19, 52 , 67, 84, 85. calcarea Tilden, 85. Cornu Damce (Roth) Ag., 85. elegans (Roth) Ag., 84 (fig. 27 C), 85. endivcefolia Ag., 85. incrassata (Hudson) Hazen., 84 (fig. 27 A and B), 85. Chaetophora pisiformis (Roth) Ag., 85. tuberculosa (Roth) Ag., 85. Chsetophoracese, 19, 26, 30, 52, 66, 67, 70, 83—89, 93, 179. Chaetophorales, 11, 15, 16, 19, 25, 30, 50, 54, 56, 66—95, 98, 180. Chsetospbasridiuin Klebahn, 52, 180, 181, 182. globosum (Nordst.) Kleb., 182 (fig. 70 A and B), 183. globosum var. depressum W. & G. S. West, 182 (fig. 70 C). minus Hansg., 182. Pringsheimii Klebahn, 182. Chamassiphon A. Br. & Grun., 343. confervicola, A. Br., 343. incrustans Grun., 343 (fig. 159). Charnaesiphoniaceae, 313, 342. Chantransia Fries, 20, 38, 39, 42. corymbifera Thur., 39. pygmaea Kiitz., 39 (fig. 2 A— C). Scotica Kiltz., 39 (fig. 2 D). Chara, 340. Characieas, 30, 179, 199—200. Characiopsis Borzi, 28, 29, 250, 251. minuta (A. Br.) Borzi, 251 (fig. 117 A). turgida W. & G. S. West, 251 (fig. 117 B— D). Charaeium A. Br., 197, 200, 219, 251. ambiguum A. Br., 200. ensiforme Herm., 200 (fig. 80 D). ornithocephalum A. Br., 200. Pringsheimii A. Br., 200 (fig. 80 A and B). Sieboldii A. Br., 200. subulatum A. Br., 200 (fig. 80 C). Chlamydococcus A. Br., 189. pluvialis (Flot.) A. Br., 189. Chlamydomonadeae, 186 — 189. Chlamydomonas Ehrenb., 3, 22, 23, 50, 51, 187, 189, 193, 202. Debaryana Gorosch., 188 (fig. 73 H and I). Ehrenbergii Gorosch., 188. hyalina, 23. Kleinii Schmidle, 188 (fig. 73 J and K). pulvisculus Ehrenb., 188. Chlorarnceba Bqhlin, 29, 30. Chlorella Beyerinck, 4, 226, 230. vulgaris Beyerinck, 230. Chlorobotrys Bohlin, 29, 249, 253. regularis (West) Bohlin, 254 (fig. 119). Chlorochytrium Cohn, 197, 198. Knyanum Szymanski, 198. Lemnae Cohn, 198 (fig. 79 A). Chlorococcum Fries, 202, 245. gigas (Kiitz.) Grun., 246. 23—2 356 Index Chlorococcum infusionum (Schrank) Menegh., 246. regulare West, 254. Chlorogonium Ehrenb., 23, 187, 188. euchlorum Ehrenb., 189. Chloromonadina (or Chloromonadales), 29, 248, 249, 253. Chlorophycese, 10, 15, 18, 19, 21, 22, 26—30, 32, 33, 50—247, 248, 270, 345, 351. Chloroplastids (or Chloroplasts), 12, 52. Chlorosaccus Luther, 29, 30. Chlorosphcera Henfrey (1858), 229. Chlorosphara Klebs (1883), 202. ChlorotheciaceaR, 29, 30, 249, 250—252. Chlorothecium Borzi, 28, 29. Chlor-zinc-iodine, 51. Choaspis S. F. Gray, 134. stictica (Eng. Bot.) O. K., 134 (fig. 50), 135. Chodat, 1, 2, 5, 21, 22, 26, 49, 90, 98, 99, 195, 201, 216, 225, 228— 230, 232, 233, 242, 308, 311. Chodat & Boubier, 50. Chodat & Cretier, 237. Chodat & Grintzesco, 9. Chodatella Lemm., 25, 232, 234. breviseta W. d- G. S. West, 234 (fig. 102 F and G). ciliata Lagerh. var. amphitricha (Lagerh.) Chod., 234 (fig. 103 H and I). radians (West) Lemm., 234. Choristocarpaceae, 45. Chromatophores, 12. Chromoplastids (or Chromoplasts), 12. Chromulina Cienk., 31. Chroococcaceue, 2, 14, 314,342, 343—352. Chroococceae, 344, 345 — 352. Chroococcus Nag., 345, 346, 352. cohaerens (Breb.) Nag., 352. giganteus West, 352 '(fig. 166 A), limueticus Lemm., 352. macrococcus Eabenh., 206. minor (Kiitz.) Nag., 352. pallidus AVV//., 352. schizodermaticus West, 352 (fig. 166 C and D). turgidus (Kiitz.) Nag., 352 (fig. 166 B). Chroocysteae, 344, 345. Chroolepm A<:., 95. Chroomonas II tiling., 32. Chroothece Hamg., 317. Richterianum Hansg., 317- Chrysomonadinaceffi, 31, 45, 46. Cieiikowski, 29, 77, 82, 84. Cladophora Kiitz., 2fi, 55, 72, 102, 104, 106, 291, 298. crispata (Eoth.) Kiitz., 105. Cladophora flavescens Ag., 105. fracta Kiitz., 106. glomerata (L.) Kiitz., 105 (fig. 40), 106. Cladophoracese, 26, 30, 33, 50, 102— 106, 107, 252. Cladophorales, 11, 16, 26, 27, 30, 56, 101—108. Cladothrix, 335. Clathrocystis Henfrey, 349, 350. teruginosa (Kiitz.) Henfrey, 350. Cleve, 293. Climacidium Ehrenb., 288. Climacosphenia Ehrenb., 283. Clonothrix qracillima W. & G. S. West, 335. Closterieee, 144, 150, 158. Closteriopsis Lemm., 218, 224. longissima Lemm., 224. Closterium Nitztch., 51, 136, 137, 140, 144, 150, 158, 159, 162. acerosum (Schrank) Ehrenb., 160 (fig. 56 A), 161. aciculare T. West, 161. acutum Breb., 160 (fig. 56 E), 161. calosporum Wittr., 161. Ehrenbergii Menegh., 139 (fig. 51 A), 161. gracile Breb., 161. Kiitzingii Breb., 161. Leibleinii Kiitz., 139 (fig. 51 B), 161. lineatum Ehrenb., 141 (fig. 52 F), 142. moniliferum (Boi~y) Ehrenb., 161. parvulum Nfig., 160 (fig. 56 F), 161. pronum Breb., 161. pusillum Hantzsch var. mono- lithum Wittr., 161. Balfsii Breb. var. hybridum Rabenh. , 142. rostratum Ehrenb., 161. rostratum var. brevirostratum West, 160 (fig. 56 G). striolatum Ehrenb., 160 (fig. 56 B— D), 161. subtile Breb., 223. turgidum Ehrenb., 161. Venus Kiitz., 161. Cocci (of Myxophycese), 313. Coccogonese, 318, 342-352. Coccomyxa Schmidle, 218. Cocconeidaceffi, 289, 290, 291. Cocconeis Ehrenb., 103. 2ttl, H>3, 290. Pediculus Ehrenb., 291. Placeutula Ehrenb., 290 (fig. 135 D— F), 291. Cocconema Ehrenb., 298, 299. cffispitosum (Kiitz.) nob., ~2(M. Cistula Ehrenb., 299. Index 357 Cocconema cuspidatum (Kiitz.) nob., 299. cymbiforme Ehrenb., 299. Ehrenbergii (Kiitz.) nob., 299. gracile (Rabenh.) nob., 299. lanceolatum Ehrenb., 299 (fig. 141 A). prostratum (Berk) nob., 299. Cocconernaceae, 291, 298 — 301. Coelastreas, 212, 213—215. Ccelastrum Nlig., 12, 25, 30, 212, 213. cambricum Arch., 213 (fig. 87 A), 214. cubicum Nfig., 214. distans Turn., 214. microporum Nfig., 214. proboscideum Bohlin, 214. pulchrum Schmidle, 214. reticulatum (Dang.) Senn, 214 (fig- 88). sphaericum Nag., 213 (fig. 87 B— D), 214, 220. subpulchrum Lagerh., 214. verrucosum Reinsch, 214. Ccelosphaerium Nfig., 311, 345, 346, 349. Kiitzingianum Nfig., 349 (fig. 163 A). minutissimum Lemm., 349. Nagelianum Unger, 349. Cohn, 3, 197, 307, 315. Cohniella Schroder, 217. Coleochaetaceaa, 17, 30, 52, 66, 67—70, 181. Coleochaete Breb., 12, 13, 54, 69, 181. irregularis Pringsh., 70. orbicularis Pringsh., 69, 205. pulvinata A. Br., 68 (fig. 17), 69. scutata Breb., 67 (fig. 16), 69. soluta Pringsh., 69. Coleospermum Kirchner, 322. Collection of Freshwater Algae, 7. Collemaceae, 325. Colletonema Breb., 292. Comere, 55. Conferva Lagerh. (and other authors), 81, 255, 256. affinis Kiitz., 258. bombycina Ag., 257, 258. fontinalis Berk., 103. obsoleta W. & G. S. West, 258. penicilliformis Roth, 75. Plinii Dillen., 256. rivularis Linn., 256. Wormskioldii Flor. Dan., 75. Confervales, 15, 28, 29, 30, 248, 249—259. Confervoidece, 21, 27. Conjugata Vauch., 159. Conjugatse, 6, 15, 17, 21, 27, 30, 32, 33, 50, 52, 54, 56, 114—178, 272. Conjugating-tube, 119. Connecting-band (of Diatom), 260. Conochsete Klebahn, 52, 180, 181, 183. comosa Klebahn, 183 (fig. 71). polytricha (Nordst.) Klebahn, 183. Cooke, 1, 2, 91. Copepoda, 4. Copeland, 126. Corbiera Dang., 187. Corda, 223. Correns, 244, 315. Coscinodiscaceae, 274, 276, 277. Coscinodiscus Ehrenb., 277. lacustris Grun., 277 (fig. 127 D). Cosmaridium Gay, 166. Cosmarieae, 144, 148, 150, 161. Cosmarium Corda, 137, 138, 144, 151, 166, 168, 169, 173. abbreviatum Eacib., 168. anceps Lund., 168. bioculatum Breb., 167 (fig. 62 I and J). Botrytis (Bory) Menegh., 168. Cucurbita Breb., 168. Dovrense Nordst., 168. granatum Breb., 167 (fig. 62 B). granatum var. subgranatum Nordst. , 167 (fig. 62 C and D), 168. Holmiense Lund., 168. humile Gay, 168. isthmium Weft, 167 (fig. 62 M). Klebsii Gutw., 139 (fig. 51 F). melanosporum Arch., 168. Meneghinii Breb., 167 (fig. 62 E— G), 168. microsphinctum Nordst., 168. moniliforme (Turp.) Ralfs, 143. obliquum Nordst., 143. ovale Ralfs, 168. Pokornyanum (Grun.) W. & G. S. West, 168. prasmorsum Breb., 167 (fig. 62 H), 168. pseudoconnatum Nordst., 167 (fig. 62 N). pygmaeum Arch., 168. pyramidatum Breb., 168. Ealfsii Breb., 168. Eegnellii Wille, 143. Eegnesii Reinsch, 167 (fig. 62 K and L). reniforme (Ralfs) Arch., 167 (fig. 62 A). subcostatum Nordst., 168. subretusiforme W.&G. S. West, 168. subspeciosum Nordst., 168. subtumidum Nordst., 168. CosmocladiumBrefi., 138, 144, 151, 173. constrictum Arch., 173 (fig. 66 A), 174. perissum Roy & Biss., 173 (fig. 66 C). 358 Cosmocladium pulchellum Breb., 173 (fig. 66 B), 174. saxonicum De Bary, 174. Cox, 265. Craterospermum Braun, 121. Craticular state (of Diatoms), 270. Crucigenia Morren, 215, 216, 217. irregularis Wille, 217. quadrata Morren, 216 (fig. 90 D and E). rectangularis (Nag.) Gay, 216 (fig. 90 A— C), 217. Tetrapedia (Kirchn.) W. <& G. S. West, 216 (fig. 90 F). triangularis Chodat, 216. Crucigenieae, 212, 215—217. Crustacea, 7, 145, 219, 270. Cryoplankton, 5. Cryptoglena Ehrenb., 32. CryptomonadinaceEe, 45. Cryptomonas Ehrenb., 45. Cryptonemiaceae, 35, 43. Cthonoblastus Ku'tz. , 332. Cultivation of Algas, 9. CyanophycecB, 3, 306 — 352. Cyanophycin, 311. Cyanoplast, 308, 309. Cycas, 325. Cyclops, 219. Cyclotella Kiitz., 276. comta (Ehrenb.) Kiitz., 276. Kutzingiana Chauvin, 276. Meneghiniana Kiitz., 276. operculata Kiitz., 276, 277 (fig. 127 B and C). Cylindrocapsa Reinsch, 54, 81, 82. conferta West, 82 (fig. 26 E and F), 83. geminella Wolle var. minor Hansg., 83. involuta Reinsch, 82 (fig. 26 A— D), 83. nuda Reinsoh, 83. Cylindrccapsaceae, 30, 66, 81 — 83. Cylindrocystis Menegh., 143, 144, 148, 149, 152, 155, 159. Brebissonii Menegh., 155 (fig. 54 H and I), 156. crassa De Bary, 156. diplospora Lund., 142, 155 (fig. 54 J), 156. diplospora var. major West, 156. Cylindrospermum Kiitz., 325, 326, 329. catenatum Ralfs, 329. macrospermum Rabenh., 329. majus Kiitz., 329. stagnale (Kiitz.) Born. t& Flah., 328 (fig. 150 E— G), 329. Cylindrotheca Rabenh., 278. gracilis (Breb.) Grun., 279. Cystocarp, 16, 35. Cystococcus Nag., 202. Cysts, 14, 102, 111, 121. Dactylococcopsis Hansg., 346, 347. montana W. & G. S. West, 348 (fig. 162 A). rhaphidioides Hansg., 348. Dactylococcus Nag., 218, 223, 348. bicaudatus A. Br., 219 (fig. 91 A), 223. bicaudatus var. subramosus W. & G. S. IFes«,219(fig. 91 B and C). Debaryanns Ileinsch, 219. dispar W. <& G. S. West, 219 (fig. 91 D). infusioniim Nag,, 219, 220. Dactylothece Lager li., 30, 33, 246. Braunii Lagerh., 206, 246 (fig. 114). Dangeard, 51, 193, 214, 310. Dasyglosa Thwaites, 330, 332. amorpha Thwaites, 331 (fig. 151 C), 332. De Bary, 142. DJybarya Wittr., 123, 124, 127. calospora (Palla) W. & G. S. West, 53, 128 (fig. 46 B). Desmidioides W. & G. S. West, 128 (fig. 46 F— I), 129, 143, 144. glyptosperma (De Bary) Wittr., 128 (fig. 46 A). Iffivis (Kiitz.) W. <& G. S. West, 128 (fig. 46 C— E). Deiniga, 308. Denticula Kiitz., 283, 285. elegans Kiitz., 283. tenuis Kiitz., 283, 284 (fig. 130 C and D). Derbes & Solier, 257. Desmagonium Ehrenb., 288. Desmidiaceffi, 5, 6, 8, 11, 14, 16, 27, 28, 30, 33, 50, 52—54, 114—116, 129, 135—178, 266, 309. Desmidieffi, 148. Desmidium Ag., 143, 144, 151, 177. aptogonum Breb., Ill (fig. 69 D). cylindricum Grev., 140, 143, 177 (fig. 69 C), 178. graciliceps (Nordst.) Lagerh., 178. quadratum Nordst.. 177 (fig. 69 B), 178. Swartzii Ag., Ill (fig. 69 A), 178. Desmonema Berk. & Thwaites, 322, 324. Wrangelii (Ag.) Born. & Flah. , 324. De Toni, 72. Diadesmis Kiitz., 292. Diatoma D. C., 284. elongatum Ag., 285 (fig. 131 A— D). hiemale (Lyngb.) Heib., 285 (fig. 131 E— F). Index 359 Diatoma hiemale var. mesodon (Kiitz.) V. H., 285 (fig. 131 G). vulgare Bory, 285. Diatomacese, 260, 281, 284, 285. Diatomaceous Earths, 271. Diatomella Grev., 282. Balfouriana Grev., 283. Diatomin, 264. Diatoms, 5, 260—305. Dichothrix Zanard., 337, 338, 339. interrupta W. & G. S. West, 339 (fig. 156 C), 340. Nordstedtii Born. & Flah., 340. Orsiniana (Kiitz.) Born. <& Flah. 339 (fig. 156 D), 340. Dictyocystis Lagerh., 235, 236. Hitchcockii (W.olle) Lagerh., 236. Dictyoneis Cleve, 293. DictyosphaerieaB, 213, 235 — 238. Dictyosphaerium Nag., 212, 235. Ehrenbergianum Nag., 236. oviforme Lagerh., 236. pulchellum Wood, 235 (fig. 104), 236. reniforme Buln., 236. Didymoprium Kiitz., 144, 177. Dill, 22, 186. Dillwyn, 1, 256. Dimorphococcus A. Br., 33, 218, 221. lunatus A. Br., 221 (fig. 93). Dinobryaceffi, 31, 45, 47. Dinobryon Ehrenb., 45, 47. cylindricum Imhof, 48. cylindricura var. divergens Lemm., 47 (fig. 7 A and B). elongatum Imhof, 48. protuberans Lemm., 48. Sertularia Ehrenb., 47 (fig. 7 C), 48. sociale Ehrenb., 48. Diplocolon Nag., 322, 324. Heppii Nag., 324. Discoideae, 273,' 274—277. Docidium Breb., 144, 150, 159, 162. asperum Breb., 153. Baculum Breb., 162 (fig. 57 A— C). undulatum Bail., 162 (fig. 57 D and E). Dolichospermum Thwaites, 327. Draparnaldia Bory, 87. glomerata (Vauch.) Ag., 87 (fig. 29), 88. plumosa (Vauch.) Ag., 88. Drosera, 129. Dwarf-male, 61. Dysphinctium Nag., 166 — 168. Edwards, 272. Ehrenberg, 265, 271. Elodea, 72, 205. Encyonema Kiitz., 299. Endoderma gracile De Toni, 205. Endosphcera Klebs, 199. Endosphaeraceae, 24, 30, 179, 197—199. Engelmann, 315. Enteromorpha Link, 30, 95, 96, 97. intestinalis (I/.) Link, 97 (fig. 35 L). Entocladia gracilis Hansg., 205. Entodesmis Borzi, 31. Epithemia Breb., 298, 300. Argus (Ehrenb.) Kiitz., 269, 300 (fig. 142 D), 301. Argus var. alpestris (W. Sm.) Rabenh., 301. gibba Kiitz., 300 (fig. 142 A), 301. gibberula Kiitz. var. producta Grun., 301. turgida (Ehrenb.) Kiitz., 300 (fig. 142 B and C), 301. Zebra (Ehrenb.} Kiitz., 301. Eremosphsra De Bary, 226, 227, 229. viridis De Bary, 229 (fig. 99). Etard & Bonilhac, 311. Euachnanthes Schiitt (sect, of Ach- nanthes), 289. Euastropsis Lagerh., 20, 206, 209, 211. Eichteri (Schmidle) Lagerh., 211 (fig. 86), 212. Euastrum Ehrenb., 137, 138, 144, 150, 164, 211. ansatum Ralfs, 165. binale (Turp.) Ehrenb., 143, 164 (fig. 60 C), 165. crassum (Breb.) Kiitz., 165. Didelta (Turp.) Ralfs, 142, 165. elegans (Breb.) Kiitz., 164 (fig. 60 A and B), 165. gemmatum Breb., 165. humerosum Ralfs, 142. insigne Hass., 165. oblongum (Grev.) Ralfs, 164 (fig. 60 D), 165. pectinatum Breb., 165. verrucosum Ehrenb., 165. Eudorina Ehrenb., 23, 30, 53, 194. elegans Ehrenb., 194 (fig. 77), 195. Eudorinella Lemm., 194, 195. Eufragilaria Ealfs (section of Fragi- laria), 286. Euglena, 23. Eumelosira Schiitt (sect, of Melosira), 275. Eunavicula Schiitt (sect, of Navicula), 293. Eunotia Ehrenb., 261, 288. Arcus W. Sm., 288. biceps (W. Sm.) nob., 289. fiexuosa var. bicapitata Grun., 289. gracilis (Ehrenb.) Rabenh., 288 (fig. 134 C), 289, 295 (fig. 137 F). lunaris (Ehrenb.) Grim., 289. 360 Index Eunotia pectinalis (Kiltz.) Rabenh., 289. pectinalis var. undulata Ralfs, 288 (fig. 134 A). robusta Ealfs, 288 (fig. 134 B). tetraodon Ehrenb., 289. Veneris Kiitz., 289. Eunotiaceae, 281, 287—289. Famintzin, 84. Fischer, 308, 309. Fischerella (Born. & Flah.) Gom., 321. Fishes, 270. Flagellata, 23, 27, 33, 185, 248. Fleissig, 109. Floridete, 34—43. Fontinalis antipyretica, 4. Foreliella Chodat, 4. Fossil Algae, 11. Fragilaria Lyngb., 285. capucina Desmaz., 286 (fig. 132 C and D). construens (Ehrenb.) Grun., 286. Crotonensis (A. M. Edw.) Kitton, 286. mutabilis (W. Sm.) Grun., 286. virescens Ralfs, 286. Fragilariaeeae, 281, 285—287. Fragilarioideaa, 263, 280—289. France, 22. Freeman, 198. Frenzel, 232. Fries, 75. Fritsch, 84, 86, 312, 313. Frustule (of Diatom), 260. Frustulia Babenh., 294. Fucoidece, 44 — 49. Fungi, 10, 314. Gaillionella Bory (sect, of Melosira), 275. Gametangia, 16. Gametophyte, 18. Gay, 20, 79, 89,. 99, 103. Geddes, 96. Geminella Turp., 26, 30, 75, 78. interrupta Turp., 78 (fig. 23 A— C). Genicularia De Bary, 53, 144, 148, 149, 153. elegans W. <& G. S. West, 153. Spirotaenia De Bary, 152 (fig. 53 I and J), 153. Gerassimoff, 123, 126, 132. Gigartinaceas, 35. Girdle (of Diatom), 260. Girdle- view (of Diatom), 261. Glaucocystaceffi, 308, 309, 317. Glaucocystidete, 3, 316, 317. Glaucocystis Itzigsohn, 317. Nostochinearum Itzigsohn, 317. Glochiococcus De Toni, 203. Glceocapsa Kiitz., 13, 246, 345, 346, 350. Magma (Breb.) Kiitz., 350, 351 (fig. 165 B). polydermatica Kiitz., 350 (fig. 165 C— E). punctata Nap., 350. Balfsiana (Hass.) Kiitz., 351. Gloeochaete Lagerh., 344, 345. bicornis Kirchn., 345. Wittrockiana Lagerh., 344 (fig. 160), 345. Gloaocystidese, 240, 244—247. Glceocystis Nag., 13, 19, 30, 242, 245, 246. ampla (Kiitz.) Babenh., 246. gigas (Kiitz.) Lagerh., 245 (fig. 113 F— H), 246. infusionum (Schrank) W. & G. S. West, 245 (fig. 113 A— E). vesiculosa Nag., 246. Gloaothece Nag., 13, 346, 347. confluens 'Nag., 347 (fig. 161 B). linearis Nitg., 347 (fig. 161 A). Gkeotila Kiitz., 20, 26, 30, 33, 75, 77, 78. protogenita Kiitz., 77 (fig. 22 C — E), 78. Glosotrichia J. Ag., 311, 337, 338, 340. natans (Hedic.) Rabenh., 89, 341. Pisum (Ag.) Thur., 341. Glycogen, 311. Gobi, 251. Golenkinia Chodat, 232, 233. paucispinosa W. <£ G. S. West, 233 (fig. 102 F). radiata Chodat, 233 (fig. 102 D and E). Gomont, 335. Gomphoneis Cleve, 297. Gomphonella Babenh., 297. Gomphonema Ag., 103, 261, 297, 298. acuminatum Ehrenb., 298. constrictum Ehrenb., 297 (fig. 140 C), 298. geminatum (Lyngb.) Ag., 297 (fig. 140 A and B), 298. parvulum Kiitz., 298. Gomphonemaceae, 291, 297, 298. Gomphosphffiria Kiltz., 346, 349. aponina Kiitz., 349 (fig. 163 B). Gonatonema Wittr., 54, 118, 122. Boodlei W. & G. S. West, 118, 122 (fig. 45 A— F), 123. notabile (Hass.) Wittr., 123. tropicum W. d- G. S. West, 118. ventricosum Wittr., 118, 122 (fig. 45 G— J), 123. Gonatozygse, 144, 149, 152. Gonatozygon De Bary, 137, 138, 144, 148, 149, 153! Index 361 Gonatozygon Brebissonii De Bary, 152 (fig. 53 A and B), 153. Brebissonii var. lawe (Hilse) W. <& G. S. West, 152 (fig. 53 C -E). Brebissonii var. minutum W. d~ G. S. West, 152 (fig. 53 F and G), 153. Kinahani (Arch.) Rabenh., 153. monotsenium De Bary, 152 (fig. 53 H), 153. Ralfsii De Bary, 153. Gongrosira Kiitz., 91, 111. stagnalis (West) Schmidle, 91, 92 (fig. 33 D— F). viridis Kiitz., 91, 92 (fig. 33 A— C). Gonidangia 15. Gonidia, 15. Gonimoblasts, 35. Goniurn Muller, 23, 30, 190, 191. lacustre G. S. West, 191 (fig. 75 B— F). pectorale Miitt., 191 (fig. 75 A), 192. sociale (Duj.) Warm., 192. Goroschankin, 22. Grammatonema Kiitz., 285. Gray (S. F.), 135. Gregarinidffi, 266. Grintzesco, 220, 230. Grunow, 270. Grunowia Eabenh., 302. Guano, 270. Gyges Ehrenb., 159. Gymnozyga Ehrenb., 144, 151, 178. moniliformis Ehrenb., 177 (fig. 69 E and F), 178. moniliformis var. gracilescens Nordst., 177 (fig. 69 G). Gynogonidia, 191. Gyrosigma Hass., 291, 292, 295. attenuatum (Kiitz.) Rabenh., 296 (fig. 138 A). Spencerii (Queck.) O.K., 296. Hcejiiatococcus Ag., 189, 206. insignis Hass., 206. Hallier, 265. Hansgirg, 1, 2, 18, 32, 126, 147, 205, 314, 315, 327. Hantzschia Grun., 301, 302. Amphioxys (Ehrenb.) Grun., 303. Hapalosiphon Nag., 38, 320, 321. Hibernicus W. <& G. S. West, 321 (fig. 147), 322. intricatus West, 322. Haptera, 12, 52. Hariotina Dang., 213, 214. Hassall, 1, 206. Hassallia Berk., 324. Hauptfleisch, 12. Hazen, 86, 189, 256. Hedgcock & Hunter, 40. Hegler, 307—311, 313. Helierella Bory, 159, 222. Helminthocladieae, 36 — 40. Henfrey, 1. Heribaud, 262. Herposteiraceffi, 30, 52, 66, 70—72, 180. Herposteiron Nag., 52, 54, 70, 71, 72, 86, 89, 180. confervicola Nag., 70 (fig. 18), 71 (fig. 19 B— D), 72. globosa Nordst., 182. pilosissima (Schmidle) nob., 71 (fig. 19 A), 72. polychsete Hansg., 72. Heterocysts, 312, 313. Heterogamous gametes (or heteroga- metes), 16. Heterokontse, 11, 29, 30, 33, 248—259. Hicks, 1. Hieronymus, 308, 310, 312, 317. Hildenbrandtia Nardo, 43. rivularis (Liebin.) J. Ag., 43 (fig. 4). Himantidium auct. var., 288. Hirn, 57, 63. Holacanthum (sub-gen, of Xanthidium), 169. Holocystis Hass., 165. Holophytes, 13. Hormidium Kiitz., 18, 98. murale Kiitz., 99. parietinum Kiitz., 99. Hormiscia Fries, 75, 76. Hormiscia Rabenh.; Hansg.; De Toni, 75, 76. Hormococcus Chodat, 79. Hormogones, 15, 313. Hormogonese, 313, 318 — 342. Hormospora Breb., 26, 30, 33, 73, 75, 77, 78, 81. mutabilis Breb., 77 (fig. 22 A). ordinata W. & G. S. West, 77 (fig. 22 B). plena Breb., 77. Hormotila Borzi, 52, 184, 201, 205, 206. mucigena Borzi, 205 (fig. 83 D). Huber, 72. Hyalotheca Ehrenb., 144, 151, 176. dissiliens (Sm.) Breb., 143, 176 (fig. 68 A— D). mucosa (Dillw.) Ehrenb., 176. neglecta Racib., 140, 176 (fig. 68 E— H). undulata Nordst., 176. Hyams & Richards, 307. Hydra viridis, 4, 230. Hydrianum Rabenh., 200. Hydrocoryne, 322. Hydrocytium A. Br., 200. 23—5 302 Index Hydrodictyaceas, 30, 180, 206—209. Hydrodictyea?, 25, 207. Hydrodictyon Roth, 11, 17, 25, 26, 30, 206, 207. reticulatum (L.) Lagerh., 208 (fig. 84), 209. Hydruraceae, 31, 45. Hydrurus Ag., 45, 46. fcetidus (Vill.) Kirchn., 46 (fig. 5). Hyphceothrix Kiitz., 330, 335. Hypnocysts, 15. Hypnaspores, 15. Ichthyocercus W. & G. S. West, 144, 149, 150. Inactis Kiitz., 330. Ineflfigiata W. & G. S. West, 235, 237, 238. neglecta W. & G. S. West, 238 (fig. 107). Infusoria, 267. Isoetes, 4. Isogamous gametes (or Isogametes), 16. Isokontas, 32. Itzigsohn, 314. Iwanoft, 86. Jackson