Classijicatioti of Green Algc?. 89 A REVISION OF THE CLASSIFICATION OF THE GREEN ALG^ BY F. F. BLACKMAN, U/weisily Lecdiirer in liutitiiy, Cambridge. AND A. G. TANSLEV, Assistant Pn/iissor of liotany. University College, London, (continued from page 72.) ^'-'Selemistnicea. Body either unicellular or an indefinite colony or a tiue ccenobium. Cell of very various shape, rarely spherical or oval, often pointed at one or both ends, very frequently reniform or seviilunar, sometimes flattened. Cell-wall typically of an inner, thin, closely-adherent membrane, and an outer, mucilaginous coat, which is sometimes produced into processes, and by which the single cells often adhere together. Chroinatopliore single, parietal, often basin-shaped, but frequently occupying nearly the whole of the cell, usually with a single pyrenoid. Reproduction by vegetative division, typically into four cells enclosed within the mother cell-wall. The four daughter cells may either separate at once by diffluence of the mother wall, or remain together, typically adhering by their mucila- ginous coats, often to form definite coenobia. Zoospores and gametes entirely unknown. [This group includes the majority of the typical Pleurococcaceae of Klebs, and seems a very natural one. The general features of the cell-type are remarkably constant and the group can be theoretically derived from a Chlamydomonadiiie ancestor in which the formation of flagella has been suppressed, and the cell has become elongated and often curved. In the simplest genera the cells live singly but shew a tendency to remain connected after division. From this type more or less definite colonies seem to have been evolved in various directions. The prevalence of the crescentic form of cell is a marked feature of the group. The name we have adopted is taken from a fairly typical genus and has the advantage of calling attention to the prevalent crescentic cell-type, as well as to the radiating structure often exhibited by the colonies.] Series A. Cells rounded or pointed and sometimes curved; floating freely, either singly, or slightly adherent to form indefinite colonies. 7. Dactylococcus.^ Na,geli, 1849. Cells oval or pyriform, often aplculate, single or loosely coherent by their pointed ends. 'This genus has generally been placed among the Tetrasporacesej and we followed tradition in including it among the genera of doubtful affinity belonging to that artificially defined family, but the most careful existing account denies the existence of zoospores, and assigns it characters which clearly give it a natural position among the lower members of our Selenas- trace<e. We have therefore introduced it again in this placet go Blackman and Tansley. 8, Raph'uVmm. Kiitzing, 1845. Cells acicular or fusiform, curved or straight, with pointed or rounded ends ; usually (ree but sometimes united in indefinite colonies. Pyrenoid usually absent. 9. Coccoiiiyxa. Schmidle, 1901. Cells oval, often slightly curved, sometimes with narrowed ends, isolated, or in pairs or fours, embedded in mucilage. Chloroplast parietal without a pyrenoid. Reproduction by vegetative division into two or four. [This appears to be a genus closaiy allied to Raphnlium and Ddclylocucciis, but adapted to aerial life.] Series B. Cells crescentic, embedded in thin mucilage, 10. NepJirocytium. Niigeli, 1849. Cells reniform, occuring in ovoid groups of 2-16, the individual cells separated from one another by mucilage and the whole group surrounded by the distended mother-cell-wall, which retains a sharp contour. 11. Kirchneriella. Schmidle, 1893. Cells semilunar or vermiform, occurring as a cluster within a mucilaginous investment, which soon becomes diffuse. C2. Selenodeniia. Bohlin, 1897. Cells semilunar, more or less widely scattered in a flat indefinite mucilaginous matrix. Serie.s C. Cells crescentic to spherical, united to form a cceiwhiuin radially symmetrical in three dimensions. 13. Selenastriuii. Reinsch, 1867. Coenobium of 4-16 crescentic cells, cohering by their convex surfaces to form an approximately centric group. 14. Sorastruin. Kiitzing, 1845. Coenobium centric, the cells being united at the centre by short stalks. Cells rounded to crescentic, with short spines exteriorly. 15. Coclastnini, Nageli, 1849. Ccenobium a hollow sphere, unually with intercellular gaps, composed of few or many cells which are spherical or polygonal. The cells are known to live singly in media rich in oxygen. Series D. Cells round to crescentic, united to form a nuiseriate colony or ccenobinjn. Classification of Green Alga. 91 iC. Dnctylotliece. Lagerheim, 1883. Cells oval, straight, or curved, grouped 1-4 in a linear series often embedded in mucilage. Division in one direction only. 17. DiniorphococcHS. A. Braun, 1849. Cells 2-8 in the coenobium, all similar and reniform, or the internal ones oval and the external semi-lunar j usually arranged in a zigzag line. 18. Scenedesmns. Meyen, 1829. Ccjenobium of 2-8 (usually 4) cells in one or rarely two rows, with rounded or pointed ends. Some or all of the cells may bear mucilaginous processes, often curved, Chromatophore filling most of the cell. Cells known to be capnble of living singly in media rich in oxygen. Series E. Cells more various in form, but often flattened, and always united in fours to form plate-like ccenobia or synccenobia. 19. Tctrastniin. Chodat, 1895. Cells flattened pyramidal with rounded corners, grouped in fours, with apices inwards and spines on the external face. 20. Ho/iiiaiiia. Chodat, 1900. Cells oval, each with a tapering hract-like mucilaginous appendage derived from the mother-cell-wall. 21. LeiiiiiiernKviiiin. Chodat, 1899. Cells flat, triangular, united by their edges in fours to form a square plate. On multiplication the daughter- ccEHobia remain closely united. 22. Actiiiasti'Uin. Lagerheim, 1882. Cells elongiited-oval or cylindrical, usually cohering by their ends to form flat radiating groups of four. Arrangement often irregular. 23. Ci'ucigcnia. Morren, 1830. Cells of various flattened forms, united directly or by processes to form a flat plate with a central perfora- tion. The coenobia are usually grouped into syncoenobia with some regularity. Daughter-ccenobia arise by division of the cell contents cross-wise. 24. Willed. Schmidle, 1900. Characters of Crucigenia, but forming an irregular plate of several hundred cells. No pyrenoid. 25. Cnicigeiiiclln. Lemmermann, 1900. Cells in fours as in Cnicigettin, but without pyrenoids. The cells divide only in the plane of the colony and the two apposed four-celled colonies thus produced soon separate. c)2 Blackmail and Ta?isley. --•"•'Pliytlieliiwcic. Plant Ijody always floating freely, unicellular or a more or less definite coenobium. Cells very »«/«(//(;,spliericalor nearly so, sometimes with a mucilaginous envelope, the walls bearing radiating bristles several times as long as the diameter of the cell. Reproduction by simple division or by the division of the cell contents into several zoospores or into aplanospore6 {"autospores") which may acquire the characters of the adult cell before or after their escape. [We have veiilureii provisionally to give the above name to a well- thanicterised aiul apparently natural group of fresh-water plankton-algae, most of which have been recently brought to liglit, mainly by the researclies of Chodat and Lemmermann, See especially lieitrilge zur Kenntniss der Planklonalgen, Hedwigia, 18!)8.] Genera, 26. Golenkiiiia. Chodat, 1894. Cells usually single, each with a single parietal cliromatophore containing one pyrenoid. Cell-wall surrounded by a layer of mucilage and bearing numerous radiating bristles. Repioduction by simple vegetative division, by quadri-flagellate zoospores or by autospores. 27. Richteriella. Lemmermann, 1896. Cells of the Goleiikinia-typs, but always united in ccenobia of 16 or 64 cells (smaller numbers may occur by some of the cells failing to divide) Cell-wall not surrounded by mucilage. Bristles only on the sides of the cells facing outwards, thick at the base, tapering. Vegetative division alone observed. 2S. Franeeia. Lemmermann, 1898. Cells oval, single or united in colonies. Cell containing 2-3 parietal chromatophores and a single vacuole; wall surrounded with mucilage. Bristles long and of uniform thickness. Vegetative division longitudinal. 29. Phythelios, Frenzel, 1891. Cells spherical, single, with radiating bristles of unifoim thickness, a single chromatophore and no pyrenoid. Reproduction unknown. [This genus was originally described by Frenzel as a Heliozoan. His species has not been seen again, but the genus has been adopted by several algologists as an alga, P'renzel's pseudopodia being interpreted as bristles. Recently another species has been described.] 30. Acanthosphaera, Lemmermann, 1899. Cells spherical, single, with a pyrenoid cell-wall very thin, usually without mulcilage, bearing numerous radiating bristles. Lower third of each bristle thick and refractive, upper two-thirds very delicate and hyaline. Reproduction unknown. Classification of Green Algce. 93 3T. Bohlinia, Lemmermann, 1899. Cells oval, single, with many radiating bristles which are thickened at their bases. Chromatophores 1-2, parietal, without pyrenoids. Reproduction by auto- spores, bristles developed while within the mother-cell. 32. Lngerhcimin. Chodat, 1895. Cells single or in coenobia of 2-8, enclosed in the mother cell-wall, ellipsoidal or cylindrical with rounded ends. Chromatophore single with one pyrenoid. Cell wall solid, bearing bristles. Bristles tapering,