Some Concepts in Mycology. William B. Brierley. 223 



But it is perhaps not sufficiently realised that our culture 

 media, our test tubes and flasks are but microcosms, and that 

 the little experiments devised in laboratories have been carried 

 out on an infinite scale by Nature for aeons of centuries. That 

 whereas in laboratories we merely change a medium from 

 saccharose to dulcite and back again, or raise the temperature 

 by ten degrees or perform some other equally trivial operation, 

 Nature offers to micro-organisms infinite permutations and 

 combinations of all the physico-chemical factors operative on 

 this earth. If therefore the little endeavours of human 

 investigators may so easily change one species into another 

 species, Nature nmst surely be doing this on an infinite scale. 

 But to admit that species in Nature are unstable and labile, 

 one instant moving in this direction, the next instant moving 

 in that as the world adjusts itself is surely a reductio ad absurdum. 

 Were it true a science of biology would be but a Utopian dream ; 

 more, we should not exist for evolution had been impossible. 



On a priori grounds therefore such quick and facile changes 

 in the ultimate physiological constitutions of organisms are 

 not only inconceivable but frankly impossible, and some other 

 interpretation of the observed phenomena must be found. 

 Such interpretations are not far to seek for they can only lie 

 in two directions. 



(i) Either the environmental factors are inconstant in 

 which case the apparently induced mutation is, as already 

 stated, merely a modification, or 



(ii) The change must exist in the organism but in some 

 other form than a change of physiological constitution. 



Recent investigations throw much light on the possible 

 nature of this change, and attention may briefly be drawn to 

 a few of the main lines of research which bear on this question. 



The crux of the problem lies principally in the initial purity 

 of the organism which is the subject of experiment, and in 

 perhaps the majority of those investigations, the results of 

 which are generally accepted as phenomena of induced mutation, 

 it is here that the interfering factor is operative. 



In the higher vegetable organisms, as in the fungi, there are 

 "physiological species" — the "species" of Lotsy(23) — within 

 the elementary species or " Jordanon"; and elementary species 

 within the Linnean species or "Linneon." In bacterial 

 categorisation morphological characters are but of little help 

 and recourse is had to the physiological reactions of the 

 organisms under standardised conditions, the bacterial species 

 being diagnosed by means of cultural data. During the last 

 few years it has been found that within the bacterial species 

 there are, frequently, very nearly allied races, often only 



