346 BOTANY. 



cells, wHch contain the oospheres ; upon coming in contact 

 with an oosphere they bury themselves in its substance, after 

 which the oosphere secretes a thick wall, and thus becomes 

 an oospore {D, Fig. 165). In gerniination (which takes place 

 after a period of rest) the protoplasmic contents of the 

 oospore become broken up into a large number of bi-ciliated 

 zoospores having nearly the shape and general appearance 

 of the spermatozoids ; these, after swimming about for a 

 time, become gradually elongated into narrowly fusiform 

 filaments, which are the young Sphceroplea individuals ; by 

 growth these take on the form and size of the adult indi- 

 viduals. 



§ II. Class OEdogonie^. 



327. — The plants constituting this well-marked class are 

 composed of articulated, simple, or branched filaments, 

 which are attached to sticks, stones, earth, or other objects 

 by root-like projections of the basal cells. The chlorophyll 

 hx the cells is always dense and uniform. They inhabit 

 ponds and slow streams, and form green masses, which fringe 

 the sticks and other objects in the water. 



328. — The CEdogonieEe are interesting for the well-marked 

 examples they afford of the intercalary growth of cells. It 

 is commonly the case that in any filament at one or two 

 points there may be seen near one end of a cell a number 

 of transverse parallel lines, which in profile have the appear- 

 ance of as many caps slipped into one another (C, Pig. 10, 

 page 32) ; these are the results of several extensions of the 

 filaments by intercalary growth. The process is as follows : 

 in a cell, a little below its upper wall, a growtn inward from 

 the surface of the wall takes place in such a way as to form 

 & cylindrical ring {A, f, Fig. 10); after a time the cell-wall 

 isplits circularly from the outside to the centre of the circu- 

 lar cylinder (/), and the two parts of the cell then retreat 

 irom each other, united only by the straightened out cylin- 

 der {B, z, Fig. 10) ; this new part elongates and the proces? 

 is repeated, finally giving rise to the series of caps first men- 

 tioned {G, c, Fig. 10), and, in conjunction with cell-division, 

 tesulting in a considerable elongation of the filaments. 



