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. 



