EVOLUTION OF PAKASITIC FUNGI. 109 



woody stem, the fungus being in fact perennial in the imperfect 

 form. 



A number of the perfect fungi reproduce the ascosporous form 

 during numbers of successive generations without the inter- 

 vention of a conidial or pycnidial form. In the case of tlie 

 imperfect forms whicli are parasitic Avhile the perfect forms are 

 saprophytic, while I have not in mind now any species' in which 

 the ascosporous form reproduces itself successively as a saphro- 

 phyte without the intervention of the imperfect form, I do not 

 doubt that there are a number of instances of such behavior. 



This peculiarity of the imperfect forms developing from year 

 to year quite independently of the perfect form has probably led 

 to a differentiation of the conidial stages of many fungi to an 

 extent which has carried some forms quite beyond the jDossibility 

 of their ever passing into the perfect form again. By this I 

 mean it is qiiite possible that following the tendency to vary and 

 produce forms which are regarded as different species, combined 

 with the habit of reproducing their own form from year to year, 

 such physiological as Avell as structural peculiarities may be 

 evolved as to so change them that they could not develop an 

 ascosporous form without an abrupt reversion or the sudden 

 evolution of a new species of the perfect form. 



During this process of differentiation of the imjjerfect form 

 into a great number of species, the ascosporous form would 

 probably for a time serve as the bond connecting all the forms 

 through which they would now and then pass. But from the 

 quite independent life and development of the imperfect forms 

 some of them would probably become so far changed that the 

 bond would no longer serve to show that they were all of one 

 stock, and we should have species of the imperfect fungi evolved, 

 which become entities in themselves. In such cases we could not 

 hypothetically say that there existed some other stage in which 

 the fungus passed the winter, or some perfect stage which carried 

 it over unfavorable periods, and that the discovery of this perfect 

 form was indispensable to the complete understanding of the 

 relation of the fungus to the particular disease in question and 

 to its etiology. 



Such is prol)ably the case in many of the parasitic species 

 belonging to the form genera Glwosporium, and Collet otrhhuvi, 



1 Certain speciea of Teichospora and Ceratertoma do iu artificial mudia. 



