212 



Transactions British Mycological Society. 



a tomato fruit which has been attacked by Botrytis cinerea 

 and of which a large portion of the surface is covered by the 

 smoke-grey conidiophores of the fungus. The following 

 possibilities are present: 



(i) The growth may consist of a single "chemical species." 



(ii) The growth may consist of two or more "chemical 

 species" growing mixed together. These would present no 

 morphological distinctions but would be separable on culture 

 media by their chemical reactions. 



(iii) The growth may consist of a single elementary species. 



(iv) The growth may consist of two or more elementary 

 species. 



[a) The species may be such as diverge on the medium. 

 An examination of the morphological characters of the growth 

 would shew considerable variations and the curves might be 

 multimodal or the separate curves might associate to form 

 one regular variation curve. With suitable cultural and 

 mechanical technique the different elementary species could 

 be isolated. Such a growth would correspond to a mixture, 

 for example of "a" and "m," representing organisms i and 2 

 developing under environment B. 



[h) The species may be such as converge on the medium. 

 The morphological variation would be comparatively small 

 and the curves would be unimodal. By transplanting the 

 growth to a series of media the components would diverge and 

 could then be isolated. Such a growth would correspond to 

 a mixture of for example " k" and "k," representing organisms 

 I and 2 developing under environment A. 



Accepting morphological comparison as a criterion of specific 

 purity, the growth would, in all the above cases, have been 

 regarded as a single species. 



Finally there is the case not illustrated in the foregoing 

 summary where the same morphological facies is presented by 

 two different elementary species growing under different condi- 

 tions — for example, " n" and " n" representing organism 2 

 under conditions C, and 3 under conditions D. 



It does not necessarily follow therefore that two fungal 

 organisms presenting identical morphological characters and 

 growing under either like or unlike conditions necessarily belong 

 to the same fungal "species" — that a Stysanus growing upon 

 a potato tuber is necessarily the same "species" as a morpho- 

 logically identical Stysanus also growing upon the tuber or 

 upon a decaying tree stump. 



This being so it must be obvious that the morphological 

 species concept — the total of individuals possessing essentially 

 similar morphological facies — is a false concept; and not only 



