232 Transactions British Mycological Society. 



It will be evident from this very brief summary* of certain 

 of the principal positive contributions to this subject, that 

 the condition of knowledge and the available evidence is not 

 such as to warrant the deducing of any, even minor, conclusions; 

 much less the elaborating of a hypothesis so subversive of the 

 foundations of biological science. 



On the other hand there is a very great deal of evidence 

 which shews that the properties of numerous organisms which 

 have been investigated have remained constant under all 

 treatment. This constancy of reaction to particular environ- 

 mental conditions has been referred to in the first portion of 

 this paper, and is the normal expectation. Conclusions such 

 as those reached by Doxig) from an intensive study of the 

 intracellular enzymes of Penicillium and Aspergillus, and which 

 are quoted below, could be multiplied almost indefinitely: 

 "There is no evidence that enzyms not normally formed by 

 the organism in demonstrable quantities can be developed by 

 special methods of nutrition. The influence of adding a 

 particular substratum to the medium is, therefore, not to 

 develop any entirely new enzym, but to stimulate the produc- 

 tion of the corresponding enzym, which is normally formed 

 under all conditions." 



In my own studies of Botrytis cinerea I have only been able 

 to educate this fungus when the initial culture has represented 

 a mixed population, and the extent of possible educability is 

 equal to that of the particular component possessing the 

 required property in the highest degree. When this strain 

 has been selected out from the population, and is dominant, 

 the organism or culture shews no further capacity for educa- 

 tion. A culture of Botrytis cinerea which contains a single 

 strain onl}^ i.e., an organism which is of specific purity, cannot 

 in my experience be educated or permanently modified in any 

 direction. 



When one considers this concept of the educability of micro- 

 organisms, and realises how pregnant with significance it is for 

 all aspects of biological science, how implicit is the allegiance 

 paid to it almost universally by students of microbiology and 

 how its far-reaching ramifications permeate all thought and 

 influence all technique in these studies, one feels that surely 

 its roots must lie deep in fact, and its truth be unimpeachable. 



* Reference should also be made to the work of Miss E. Schiemann on 

 mutations in Aspergillus niger (Zeit. f. indukt. Abstamm. v. Vererbungslehre 

 viii. 191 2). Colour modifications in this fungus may readily be produced but 

 Miss Schiemann's work stands alone in that the induced changes were per- 

 manent. Until the circumstances obscuring the genetic constitution of this 

 fungus are made more clear, and the results are confirmed under more rigidly 

 controlled conditions, one must hesitate in accepting this unique work. My 

 own repetition of these experiments has given absolutely negative results. 



