50 Transactions British Mycological Society. 



plastic and interacts with a given en\dronment to produce a given 

 result; but whether any part of the interacting force-system 

 "Organism" remains unmodified by its successive contacts with a 

 series of other force-systems "Environment i," "Environment 2," 

 and so forth, is unproven and perhaps unprovable. It is more- 

 over antecedently improbable. The only factor possessing any 

 demonstrable rigidity is the standardised environment and it is 

 much more economical of hypothesis to suppose that constancy 

 of reaction is assured by the conformation of the plastic living 

 constitution to it. The possibility of such conformation will 

 naturally govern the viability of the organism in that environ- 

 ment and the act of conformation moulds it into the appropriate 

 form, but neither form nor conformation have any individuality 

 apart from the environment which elicits them from the 

 organism; while the latter, primordially amorphous, responds 

 in a series of symmetrical fashions to every external impress 

 within the limits of its inherent plasticity. Each fashion of 

 response represents one of the despised "evanescent morpho- 

 logical facies," which however exist and which alone have been 

 demonstrated to exist. 



The unproven assumption of a permanent physiological con- 

 stitution (impl3dng of course genetic constitution) underlying 

 all phenotypic changes, permeates and vitiates the whole con- 

 cept of the ideally pure species. The generations of a pure line 

 are supposedly linked together by some character or characters 

 which do not change and are therefore the true " specific indices," 

 but it is logically impossible to prove that any such characters 

 are altogether inaccessible to external influences. Experimental 

 evidence, be it never so searching, is necessarily inconclusive, 

 since whatever character we select for test the negative cannot 

 be proved. Yet even \^dthin the limits of available experimental 

 evidence there is material enough to support the positive, that 

 every unit character, or, to confine ourselves strictly to de- 

 monstrabilities, the degree of expression of every unit character, 

 is thus amenable to environmental control. Whether there is 

 any absolute constant behind this "degree of expression" is 

 exactly what has been called into question as unproven. The 

 morphological facies is indeed the outward and visible sign of 

 the metabolic rhythm, but is not this in its turn largely the 

 reflection of its circumstances and neither the form of the one 

 nor the other wholly self-existent? That the protoplasm does 

 indeed maintain throughout all the situations in which it may 

 find itself, some elements of continuity, relatively stable over 

 moderate periods of time, is obvious; but these elements are, 

 in general, much more fundamental than the unit distinctions 

 of species, involving the degree of complexity of the plasma 



