OOSPORES 



133 



1 66. As a representative of the Oosporese, the filament- 

 ous fresh-water Alga, (Edo- 

 gonium, may be mentioned. 

 It grows in ponds and 

 streams, and forms green 

 masses attached to sticks or 

 other objects. When ex- 

 amined under the micro- 

 scope, a number of transverse parallel lines near one end 

 of the cell will be seen, and in section they appear as so 

 many cups slipped over each other (Fig. 249). This results 

 from its peculiar mode of intercalary growth, as follows : 

 an inward growth from the wall takes place in such a way 

 as to form a cylindrical ring (Fig. 249, J). After a time, 

 the cell-wall splits circularly through the exterior portion 

 of the ring, and the two portions of the cell-wall recede 

 from each other, connected by the unfolded cylinder (Fig. 

 249, II). The cell elongates again by the formation of a 

 new ring below the previous one, and so on. The non- 

 sexual reproduction takes place by the formation of 

 ciliated, motile zoospores (Fig. 248) ; when the spore 

 (zoospore) comes to rest, and forms a cell-wall, it sends out 

 root-like projections for attachment, then 

 elongates, forms cross-partitions, and takes 

 on the form of the adult filament. The 

 sexual reproduction takes place by the for- 

 mation of an oosphere in an enlarged cell of 

 the filament, the oogonium ; this then opens, 

 and allows the entrance of the sperma- 

 249 tozoids, which have a crown of cilia, like 



Fig. 248. Non-sexual reproduction of OEdogonium, Fig. 249. Diagrammatic 

 representation of intercalary growth of the (Edogonlum. 



