292 



PART IV. VEGETABLE TAXONOMY. 



It not infrequently happens, also, that soon after the germi- 

 nation of the spore, rejuvenescence takes place ; that is, the wall 

 ruptures and the protoplasm escapes to 

 form a new cell, which sooner or later 

 again germinates. See Fig. 488. 



In the sexual reproduction, one or 

 more of the cells of the filament become 

 greatly enlarged to form oOgonia. When 

 mature, an opening or pore is formed in 

 their walls and antherozoids, produced 

 either on another filament or in other 

 cells of the same filament, find their way 

 through the openings and fertilize them. 

 This is the common mode ; in other cases, 

 however, small ciliated cells, called andro- 

 spores, are produced either in a male fila- 

 ment, or in other 

 cells of the same 

 filament that pro- 

 duces the oogo- 

 nia ; but these, instead of directly fer- 

 tilizing the latter, become 

 attached by a root -like 

 process to it or near it, lose 

 their cilia, grow into a short 

 filament, and finally the ter- 

 minal cell of the latter 

 ruptures, setting free a mi- 

 nute antherozoid, which 

 penetrates the aperture of 

 the oogonium and fertilizes 

 the oosphore. See Figure 

 489. 



Fig. 489. — Oedogonium ciliatum, showing mode of sexual reproduction. A, portion of 

 male filament producing androspores b and c. B, portion of female filament producing 

 oogonia e, e, e ; _/, /, male plants produced from androspores, which have germinated on 

 the sides of two of the oogonia, and are each discharging a minute antherozoid. The fila- 

 ment has partially broken apart, leaving an opening in the top of the lower oogonium, so 

 that the antherozoid may enter. This end of the oogonium is filled with mucilage, which 

 slightly protrudes from the opening. C, a ripe oogonium, which has separated from the 

 filament. D, represents the production of four ciliated spores from the protoplasm of the 

 germinating oospore. 



Fig. 488. — a, young plant 

 of Oedogonium reproducing 

 itself by rejuvenescence ; b, 

 the escaped protoplasm after 

 it has acquired cilia. Mag- 

 nified about 250 diameters. 



