1885.] 



MICROSCOPICAL JOURNAL. 



109 



Cells like CJiaraccum. contents con- 

 tracted into a ball. 



Hydrianuviy 35. 

 Cells stiptate, in tufts. ,CodioIum^ 36. 

 Cells cylindrical, cuived, free. 



Ophiocytium^ 37. 

 b. Individual cells united in a coeno- 

 bium-liketamilv, which, however, dif- 

 fers from a true caMiobium, in that their 

 cells are not all of one and the same 

 <2^eneration. Zoospores by simulta- 

 neous division. (Pseudoccenobi.e.) 



Syuopsis of Genera. 

 Elongate cells, spreading from end of 

 mother-cell, forming tree-like fami- 

 lies. Sciadhim^ 38. 

 r. Individual cells united in coeno- 

 bia. or femilies of definite form, pro- 

 duced by the growth of daughter-cells 

 of one and the same mother-cell. 

 These plants differ from the multi- 

 cellular alga^ in that the single cells 

 show no vegetative division. (Cceno- 



Synopsis of Genera. 

 Elongate cells in series of 2-8 side bv 

 side. Scenedesmus., 39. 



Coenobium globose, solid ; cells angu- 

 lar, two spines at angles. 



Sorastruni^ 40. 

 Cells half-moon shaped, convex mar- 

 gins joined in coenobia of 4-8. 



Se/enastrzim, 41. 



Coenobium spherical, hollow, cells in 



a single reticulate layer near the 



surface. Coelastriim^ 43. 



Coenobium flat, round or oval. 



Pediastrum ^ 43. 

 Coenobium a net, formed of cylindri- 

 cal cells placed end to end forming ' 

 the meshes. Hydrodictyon^ z|4. I 

 Genus of doubtful value omitted 

 (combined with Characeum .■x,'^'- — 

 Hydrocytium . 

 a. Eremobi.'E. 

 31. Genus Polyedrium Nageli. 

 Cells single, angular, free swim- 

 ming, three or more angled, the cor- 

 ners lying in one plane, or tetrahe- 

 dral ; contents chlorophyll - green , 

 often with red spots. 



Propagation by gonidia, 3-4 form- 



ing of the contents of one mother-cell, 

 which pass out through an opening 

 in the wall, covered w^ith a delicate 

 envelope and grow separately. 



Apparently some of the species 

 here placed belong in the develop- 

 ment-cycle of coenobian protococca- 

 cCcE, and correspond to the so-named 

 polyedern of Hydrodictyon obser\'ed 

 bv Pringsheim, from which, by free 

 cell formation, new hydrodictyon- 

 nets develop. 



[Some of the forms bear close re- 

 semblance to certain desmids, especi- 

 ally to members of the large genus 

 Staurastrnm. Their mode of pro- 

 pagation is quite different.] 



32. Genus Protococcus Agardh. 



Cells spherical, not attached, sin- 

 gle or in irregular masses, with green 

 or red contents, a starch granule and 

 vacuole. Zoospores formed by suc- 

 cessive binary division. 



[The appearance of Protococcus is 

 so very much dependent upon condi- 

 tions, that it is not possible here to 

 describe its many transformations. 

 When in the water the cells may be 

 actively swimming about, but most 

 frequently it will be recognized as a 

 thin, powdery layer of cells, or, in 

 the presence of abundant moisture, 

 the cells may be surrounded by gela- 

 tinous envelopes. It occurs on bark 

 of trees, damp walls, etc., and seems 

 to be not unfrequently confounded 

 with Pleurococcus., which is found in 

 similar places. It is, indeed, doubt- 

 ful if the two genera are distinct, al- 

 though PIet(rococcus is seldom ob- 

 served except in the vegetative con- 

 dition, while Protococcus is more 

 ready to pass into the motile condi- 

 tion in the presence of water. 



It is more than probable that many 

 of the plants included in this genus 

 belong to the life-cycles of higher 

 algs.] 



33. Genus Chlorockytrium Cohn. 

 Endophytic plant. Cells spheincal, 



oval, kidney-shape, or 2- 3- multi- 

 lobed, single or in groups in the in- 

 tercellular space of the parenchyma 

 of w^ater-plants. Numerous zoospores 



