54 Transactions British Mycological Society. 



organismal characters is a purely relative term and the apparent 

 stability of some characters, generic and familial characters for 

 instance, is accounted for, in the first place, by their more 

 fundamental nature and the consequently greater length of 

 time during which the organism has been in the habit of pro- 

 ducing them, and secondly, by the restricted experimental 

 possibilities, chiefly from the point of view of the required time, 

 which limit us in attacking these primordial habits. Given 

 sufficient time to produce acclimatization to fundamentally 

 different conditions it would be difficult to set a theoretical limit 

 to the extent to which we could mould the habit of our species. 



It helps us likewise to emphasize the fallacy of the hunt for 

 a wholly objective definition of the term species; a wild-goose 

 chase after that illusion the pure species, which, apparently 

 alone in the universe, maintains an aristocratic reserve of con- 

 stitution, chemical or otherwise, relative to no basis but itself. 



Chemical analogies, indeed, of the reaction of organism and 

 environment are somewhat dangerous. Even if it be true that 

 each species has a particular chemical composition, a specific 

 protein, it is impossible to imagine that this modern version of 

 the idioplasm undergoes no tautomeric changes in relation to 

 its environment. The very elements are no longer the immutable 

 constants that they once seemed. If such analogies really 

 illustrate anything it is that both parties to the reaction, 

 i.e. both protoplasm and environment, in our terminology, enter 

 in greater or less degree into the actual constitution of the final 

 product — the visible organism. 



Nor is there any particular stage in its life-history at which 

 a species may be considered as having withdrawn its constitution 

 entirely from contact with the environment. There is no goni- 

 dium so dormant that it is wholly unresponsive to such funda- 

 mental factors as light and temperature : some indeed are quite 

 remarkably sensitive. Moreover it is needless to labour the 

 fact that the form of the mature individual is never wholly pre- 

 determined by the constitution of the antecedent gonidium. 



Over against all such considerations we have to recognize the 

 very high degree of constancy exhibited by many species in 

 nature, a constancy to which the systematist is justified in 

 pointing as a vindication of his general morphological usage in 

 dealing with species. 



There is no necessary contradiction between this observed 

 fact and the foregoing ideas about the specific form as an en- 

 vironmental reflex. Many species are accurate environmental 

 indicators; the given organism is never found apart from the 

 given conditions, so that the recognition and description of the 

 species are immediately possible without recourse to physio- 



