306 PHYSIOLOGY OF THE FUNGI 



that certain helpful generalizations concerning sporulation cannot be 

 drawn. It does, however, imply that the only sure way of understanding 

 the conditions governing reproduction in a specific fungus lies in the 

 experimental approach. 



Again it must be emphasized that all the physical and chemical condi- 

 tions may be at the optima, but no reproduction can occur without the 

 presence of favorable genetic factors. Too often we may fail to realize 

 the genetic requirements. The appropriate steps should be taken to 

 determine whether the fungi under study are homothallic or heterothallic. 

 It may be difficult, indeed, to determine whether failure of a fungus to 

 reproduce in culture is due to unfavorable environmental conditions or 

 to unfavorable genetic factors. There is much yet to be learned regard- 

 ing the physiology of reproduction, but each new investigation is certain 

 to add to our knowledge of this interesting and important phase of fungus 

 physiology. 



Vegetative growth must precede reproduction. The length of the 

 vegetative phase varies from organism to organism, and the same organ- 

 ism may remain in the vegetative phase for a longer or shorter period of 

 time depending upon the external environment. One of the functions 

 of the vegetative phase is concerned with the building up of protoplasm 

 and the storage of energy reserves. Reproduction is a process that draws 

 heavily on the reserve food. The spore is usually well stocked with these 

 materials. Asexual reproduction differs less from vegetative growth than 

 does sexual reproduction. We shall find that the conditions limiting- 

 sexual reproduction are usually more narrow than conditions which allow 

 asexual reproduction and growth. 



Klebs (1900) summarized his views on reproduction in the fungi in the 

 form of four laws or principles as follows: (1) Growth and reproduction 

 are life processes, which, in all organisms, depend upon different condi- 

 tions. In the lower organisms the external conditions mainly determine 

 whether growth or reproduction takes place. (2) Reproduction in the 

 lower organisms does not occur as long as characteristic external condi- 

 tions are favorable for growth. The conditions which are favorable for 

 reproduction are always more or less unfavorable for growth. (3) The 

 processes of growth and reproduction differ, in that growth may take 

 place under a wider range of environmental conditions than reproduction. 

 Growth may take place, therefore, under conditions which inhibit repro- 

 duction. (4) Vegetative growth appears to be mostly a preliminary step 

 for reproduction in that it creates a suitable internal environment for it. 

 To a certain degree it is not growth in itself but the prolonged period of 

 assimilation accompanying growth that is decisive for reproduction. 



These generalizations were published in 1900 and were based upon 

 Klebs's own work, as well as that of others. Many more fungi have been 



