252 BOTANY. 



directly into now plants. In still other species the spore 

 forms us in the lust case, but there is a dehiscence of the sur- 

 rounding wall which permits the spore to slip out ; it begins 

 to germinate soon. In some species, instead of forming a 

 spore, the naked protoplasm in the swollen branches, after 

 condensing somewhat, escapes into the water through a 

 fissure in the cell-wall, and becomes a zoospore (A, Fig. 

 168) ; it is covered throughout its whole surface with delicate 

 vibrutile cilia, by means of which it moves through the 

 Avater (Fig. 169). After a short period of activity the zoo- 

 spores come to rest, their cilia disappear, and a wall of cellu- 

 lose is formed (B, Fig. 168) ; in this condi- 

 tion (the zoogonidium) they remain for some 

 hours, when they begin to germinate by 

 sending out one or two tubes (C, D, Fig. 

 168) ; the root-like organs grow either direct- 

 ly from the zoogonidium (F, Fig. 168), or 

 from one of the tubes (E, Fig. 168). 



336. Sexual reproduction takes place in 

 lateral branches also. Both antheridia and 

 oogonia develop as lateral protuberances upon 

 the main stem (og, og, h, Fig. 168). They 

 vwKhe- ori g inate as diverticula of the principal cavity 

 a, ecto- (4 oq, h, Fig. 170) ; these develop on the one 



plasm bearing the v ,* 



cilia ;&, endophism. hand into male organs, and on the other 



X eOO.-Osmic acid . , , . mi i 



preparation, after mto female organs. The male organ is long 

 and rather narrow, and soon much curved 

 (B, 0, Fig. 170) ; its upper portion becomes cut off by a 

 partition, and in it very small bi-ciliate spermatozoids (I), 

 Fig. 170) are developed in great numbers. The female or- 

 pin is short and ovoid in outline, and usually stands near 

 the male organs. In it a partition forms near its point of 

 union with the main stem ; the upper portion becomes an 

 oogonium, and its protoplasm condenses into a rounded 

 body, the oosphere (6 v and E, Fig. 170) ; at this time the 

 wall of the oogon in m opens, and permits the entrance of the 

 spermatozoids which were set free by the rupture of the 

 antheridium-wall. Upon coming into contact with ^he 

 oosphere the spermatozoids mingle with it and disappotir ; the 



