SEXUAL REPRODUCTJON'. 



293 



Loss of sexuality. 



396. Among fungi. — 'I'hmigh desc ended from ancestors 

 ])Ossessing sexual organs, certain groujis of" plants ha\e lost this 

 mode of reproduction and rely wholly upon non-sexual 

 methods. Such are the higher 

 fungi. The lo^'er forms only 

 have sexual organs. These fungi 

 show their relation to alga; by 

 retaining in part or wholly a(|ua- 

 tic habits. In Cvs/opus, for ex- 

 ample, at a certain stage zo- 

 os[)ores are produced ; and these / " 

 are generally characteristic of 

 aquatic plants, though Cxstttptis ~>C 



has become a parasite upon land 

 plants. Many aquatic fungi are 

 known, most of which grow 

 upon dead plants or animals 

 (especially insects) which ha\e r"^ X 

 fallen into the water. Not only 

 do man\' of these lower forms 

 produce zoospores, but the form 

 of their sex-organs and mode 

 of union remind one immedi- 

 ately of similar structure and 

 action in common alg;e. Com- 

 liare, for example, the sex-organs 

 in Vaucheii'a (fig. 308) and those oi Achlvo (fig. 336). 



Some fungi possess sex-organs which are functionless 

 although the egg de\-elops as though it had been fertilized (fig 

 336). But in most, all trace of sexual organs has disappeared, 

 though many produce spore-bearing structures, the fructifica- 



/ -I 



Fui. 330. — A. 1' uinjtionlt^s stx-urgans 

 of a fungus {A^slilya /r^iiiciUa). 

 IJvaries globular, with 2-4 egg.s ; 

 sperniaries from branches of same 

 liypha form fertilizing tube which re- 

 mains closed. />', eggs which ha\-e 

 become resting spores without ferti- 

 lization. Magnified 365 diaiu. — .After 

 .■^ach-s. 



