CHAPTER II 



PHYSIOLOGY OF FUNGI WITH SPECIAL REFERENCE 

 TO REPRODUCTION 



The life of a fungus may be divided into three periods: (1) vegetative 

 growth, (2) multiplication by asexual means, and (3) the development of sex- 

 ual organs usually resulting in a spore able to resist unfavorable factors of 

 the environment. Since studies of classification and evolution of the various 

 groups of fungi are usually based on this last stage which presents the great- 

 est diversity of phenomena, much of laboratory work in the last half century 

 has been directed toward securing the production of sexual stages. After 

 Bary, Brefeld, Hansen and Zopf had developed the technic of cultivation, 

 Klebs in the years from 1896 to 1904 laid the foundations of much of our pres- 

 ent knowledge by detailed studies of the conditions necessary for vegetative 

 growth and reproduction in a few organisms. Subsequent work of C. H. 

 Kauffman and his students has done much to extend Klebs' generalizations to 

 further groups of fungi and to confirm his well-known dicta. These may be 

 summarized as follows : 



1. Among all organisms, growth and reproduction are life processes, 

 Avhich depend upon different conditions : among lower organisms, probably 

 environment determines whether growth or reproduction will occur. 



2. As long as the environment is favorable for growth, reproduction will 

 not occur. An environment favoring the latter is usually more or less un- 

 favorable to further growth. 



3. The limits of each factor of the environment are narrower for reproduc- 

 tion than for growth. Therefore growth can still take place, although repro- 

 duction is limited by a too weak or too strong influence of some factor. 



4. Before reproduction can occur growth must have been sufficient to 

 have stored the products necessary for the reproductive processes. 



As a consequence of these dicta, most specialized methods for securing 

 sexual or even asexual reproduction in a given group consist essentially in 

 growing the organism for a time as nearly at optimum conditions as possible, 

 then suddenly changing one or more factors of the environment to a condition 

 less favorable for growth but still within the limit for reproduction. Exam- 

 ples of this will be given in the following analysis of some of the chief factors 

 of the environment. 



Water. — The water requirement and transpiration have been little studied 

 in fungi. While spores often have mechanisms for resisting desiccation over 

 long periods and some very complex specialized structures are developed 

 among the higher fungi for preventing the reproductive organs from drying 

 out, in general the fungi both grow and reproduce in relatively high humidi- 



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