253 



BOTANY. 



•directly into new 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 

 \ibratile 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 to germinate by 

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

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

 ly from the zoogonidiuin (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 (pg, og, Ti, Fig. 168). They 

 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 

 into female organs. The male organ is long 

 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 (D, 

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

 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 E, 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 

 the surface of a zo- 

 ospore of Vaui^- 

 •HasessUis. a. ecto- 

 plasm bearing the 

 <:ilia ; b, endoplaem. 

 X 600.— Osmio acid 

 preparation, after 

 Strattburger. 



