OOSPORES. 



%n 



so that these pieces, forming small projections, give to the upper end of the cell the 



1^^ appearance of consisting of caps placed one over another, while the lower end of the 

 I^B cells appears to be enclosed in a long sheath (the lower old piece of cell- wall). This 

 ^* lower part of an elongated cell is always separated by a septum from the upper cap- 

 bearing piece (see Fig. 17, p. 22). In Bulbochgete the growth of all the shoots, even of 

 the first which proceed from the spores, as far as it depends on cell-multiplication, 

 is limited to the division of their basal cell ; it follows therefore that the cells of each 

 shoot must be considered to be the basal cells of the lateral branches which stand upon 



FIG. 182. — Development of -the zoogonidia of FIG. 183.— ^ CEdogonium ciliatum (X 250) middle part of a sexual filament 



(Edogonhitn (after Pringsheim). A, B their origin with an antheridium (tn) at the upper end, and two fertilised oogonia (og) and 

 from an older filament ; C free zoogonidium in a dwarf male plant m ; B oogonium at the moment of fertilisation ; o the 

 motion ; D commencement of its germination ; oosphere, z the antherozoid in the act of forcing its way in, nt dwarf male 

 E a zoogonidium formed out of the entire contents plant ; C ripe oospore ; D piece of the male filament of O. gemelliparttni, 

 of a germinating plant (X350). z antherozoids. £ branch of a hybernated plant of Bulbochate intermedia, 



with one oogonium still containing a spore, another in the act of allowing it to 

 escape ; in the lower part an empty oogonium. F the four zoospores result- 

 ing from an oospore; G zopspores from an oospore come to rest (after 

 Pringsheim). 



them. The cells contain chlorophyll-grains and a nucleus in a parietal layer of proto- 

 plasm. The zoogonidia, as well as the oogonia and antheridia, are formed from cells of the 

 filaments, which only become enlarged and assume a more or less spherical form when 

 they give rise to oogonia. From the oospores which have remained at rest for a con- 

 siderable period several (usually four) zoospores are immediately formed, which produce 

 asexual, i. e. zoogonidia-forming plants, from which again similar ones proceed, until the 

 series of them is closed by a sexual generation (with formation of oospores) ; but the 

 sexual plants produce zoogonidia as well. The sexual plants are either monoecious or 

 dioecious ; in many species the female plant produces peculiar zoogonidia (Androgonidia), 



