STROPHARIA EPIMYCES 169 



piperatus ^ for the species of Hypomyces are usually saprophytes 

 on dead agarics. However, it does not seem suited to explain the 

 origin of the parasitism of our Stropharia on Coprinus ; for, at the 

 present day, Strophariae saprophytic on dead agarics are unknown. 



(2) The second possibility is that originally the Stropharia 

 and a Coprinus came into contact as saprophytic competitors for 

 the same nutrient substratum and that, subsequently, the Stro- 

 pharia gave up its saprophytic mode of existence and became 

 directly parasitic upon the living Coprinus. A parallel for this 

 second supposition is to be found in the probable origin of the para- 

 sitism of Rhinanthus, Bartsia, Euphrasia, etc. These green root- 

 parasites, at first, were doubtless holophytic like the other Scroph- 

 ulariaceae ; and then, in all probability, they became directly 

 parasitic on the living grass plants and other herbs with which they 

 at first competed on equal terms. It is also probable that Cuscuta 

 changed directly from being a holophyte, like its near relative 

 Convolvulus, to being a parasite. 



(3) The third possibility is that originally there was a Stropharia 

 which lived saprophytically on dung or some other dead organic 

 substratum, and that the spores of this fungus underwent an internal 

 physiological change which enabled them to germinate successfully 

 and produce a mycelium, not only on their customary dead organic 

 substratum , but also on a living Coprinus. Thus, owing to a relatively 

 slight, although important, evolutionary saltation, the Stropharia 

 suddenly became a successful parasite. Later on, we may suppose, 

 it became specialised for its parasitic mode of life and ceased to live 

 saprophytically. 



It seems almost impossible to explain the manner in which the 

 highly specialised parasitism of the Uredineae came into existence 

 unless one supposes that, from time to time in the course of evolution, 

 the spores of certain species suddenly acquired new powers which 

 enabled them successfully to attack previously immune phanero- 

 gamic host-plants. Thus the evolution of parasitism in our Stro- 

 pharia epimyces and in the Rust Fungi may well have been due to 

 the same fundamental factor. 



Whatever may have been the exact origin of the parasitism of 

 1 Cf. vol. ii, 1922, pp. 58-69, Figs. 17-19. 



