416 PHYSIOLOGY OF THE FUNGI 



The basis for permanent variation in imperfect fungi (as well as in other 

 groups) is believed by many to be true mutation. There is circumstantial 

 evidence that many such sudden changes are mutations, but the inherit- 

 ance of such a change in the imperfect fungi cannot be proved. Other 

 variations in the imperfect fungi are explained on the basis of hetero- 

 caryosis. Separation of such nuclei into different spores would result in 

 the segregation into different mycelial or sporulating types. Thus, the 

 dual phenomenon would explain many of the variations in the imperfect 

 fungi. 



The type of variation known as physiological specialization is of prac- 

 tical interest and importance among the pathogenic fungi. Pathogenicity 

 on a number of varieties of hosts offers a rigorous test to distinguish races 

 which differ perhaps only slightly in their physiology. The future of the 

 work dealing with physiology and genetics of the fungi lies principally 

 in the hands of competent, well-trained investigators who may be inter- 

 ested enough to spend much time and effort in this narrow field of investi- 

 gation. Many problems in this field are waiting to be solved. 



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