263 



BOTANY. 



directly into now plants. In still other species the spore 

 forms as in the last 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 

 ■vibratile cilia, by means of which it moves through the 

 water (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 tp germinate by 

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

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

 ly from the zoogonidium (i^. 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, Ji, Fig. 168). They 

 oroore "^^iT %uaS^ originate as diverticula of the principal cavity 

 (A, og, h, Fig. 170) ; these develop on the one 

 hand into male organs, and on the other 

 prepaiationr'''aner into female organs. The male organ is long 



Strasburger. j j.i j i j 



and rather narrow, and soon much curved 

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

 partition, and in it very small bi-ciliate spermatozoids {B, 

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

 gan 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 (Cand B, Fig. 170) ; at this time the 

 wall of the oogonium opens, and permits the entrance of the 

 spermatozoids which were set free by the rupture of the 

 antheridium-wall. Upon coming into contact with the 

 oosphere the spermatozoids mingle with it and disappear ; the 



Fig. 169.— Section 

 at right angles to 



oppore of Vauohe- 

 riaitessitis, a, ecto- 

 plasm bearing the 

 cilia ; b, endoplasm. 

 X 600.— Osmic acid 



