SEXUAL REPRODUCTION. 



293 



Loss of sexuality. 



396. Among fungi. — Though descended from ancestors 

 possessing sexual organs, certain groups of plants have lost this 

 mode of reproduction and rely wholly upon non-sexual 

 methods. Such are the higher 

 fungi. The lower forms only 

 have sexual organs. These fungi 

 show their relation to algae by 

 retaining in part or wholly aqua- 

 tic habits. In Cys/opus, for ex- 

 ample, at a certain stage zo- 

 ospores are produced ; and these 

 are generally characteristic of 

 aquatic plants, though Cys/opus 

 has become a parasite upon land 

 plants. Many aquatic fungi are 

 known, most of which grow 

 upon dead plants or animals 

 (especially insects) which have 

 fallen into the water. Not only 

 do many 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 algae. Com- 

 pare, for example, the sex- organs 

 in Vaucheria (fig. 308) and those of Achlya (fig. 336). 



Some fungi possess sex-organs which are functionless, 

 although the egg develops 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- 



Fig. 336. — A. Functionless sex-organs 

 of a fungus (Achlya lignicola). 

 Ovaries globular, with 2-4 eggs; 

 spermaries from branches of same 

 hypha form fertilizing tube which re- 

 mains closed. B, eggs which have 

 become resting spores without ferti- 

 lization. Magnified 265 diam. — After 

 Sachs. 



