CHAPTEE XXIII 



SUMMARY OF THE LIFE HISTORIES AND EVOLUTION 



OF THE FUNGI 



280. The life histories of the fungi. To understand the 

 types of life histories in the different groups of the fungi one 

 must bear in mind the life histories of the most nearly related 

 groups of algas (Sec. 247), for those of the fungi are based, of 

 course, on the life histories of their algal ancestors. But there 

 have been some very important modifications as the result of 

 the parasitic and saprophytic modes of life of the fungi, and 

 especially because the highest groups of fungi present much 

 sexual degeneration, or apogamy, which of course in some 

 respects simplifies the life histories. 



The life history of the bacteria is essentially as simple as 

 that of the blue-green alg;e. The alga-like fungi (Pliycomycdes) 

 is a group, however, whose highest members (the molds, water 

 molds, and blights) have reproductive organs with many points 

 of similarity to the siphon algae, and more especially to Vau- 

 cheria (Sec. 228). The sexually formed spores generally develop 

 directly into plants like the parents, 1 so that the formula for the 

 life history is 



P <C > sex. s. P<^y^> sex. s. P. etc., 

 ff" "0- 



the abbreviations g and sex. s. standing for gamete and sexually 

 formed spore, respectively. There is often extensive reproduc- 

 tion through various forms of asexual spores between succes- 

 sive sexual generations. And indeed sexual organs may only 

 be formed at rare intervals, as in the bread mold, or they may 



1 They form zoospores, however, in some of the blights. 



272 



