220 Transactions British Mycological Society. 



And in 1915 Massee(25) wrote "That parasitism on the part 

 of fungi is an acquired habit has been fully demonstrated and 

 is generally accepted," and earlier, "A saprophytic fungus 

 can be gradually educated to become an active parasite to a 

 given host plant. . ." 



In his recently published work on "Fungi and Disease in 

 Plants," Butler(.5) has written: "Certain saprophytes have 

 been found at times to become 'educated' into the parasitic 

 life; that is to say, it has been found possible to develop a 

 parasitic strain, or race, of a normally saprophytic species, 

 capable of living even on healthy individuals of the host plant." 



Pringsheim(34), Dobell(8), Eisenberg(io) and Vaughan(47) have 

 within recent years drawn up careful summaries of the evidence 

 relative to this question and references to the greater part of 

 the literature will be found in their compilations. 



At first sight the weight of evidence on which the concept 

 of the educability of micro-organisms is based appears so 

 overwhelming as almost to preclude doubt. But first-hand 

 acquaintance with certain of the described phenomena, and 

 a more critical examination of the literature of the subject, 

 raise disquieting suspicions that possibly investigators have 

 been too facile in their interpretations of the phenomena 

 observed and over hasty in drawing general conclusions. 



In the first place it is very necessary to have sharply in 

 focus what we mean when we speak of educating organisms 

 or of inducing permanent changes in their characteristics. The 

 changes which have been recorded in the lower organisms are 

 of two essentially different kinds. One consists of those 

 alterations which are impermanent, their expression depending 

 upon particular factors in the environmental conditions. This 

 category includes all the expressions of the plasticity of organ- 

 isms which have already been referred to as "modifications." 

 Such modifications are strictly comparable with the "ecads" 

 or growth variants of for example Polygonum amphihium or 

 other plastic phanerogams. If the individuals are returned 

 to their original environmental conditions they revert strictly 

 to type. 



The second category includes all those alterations — however 

 small they may be — which take place in an organism and are 

 then transmitted to subsequent generations even when these 

 are again grown under the original environmental conditions. 

 As illustrations of such changes the work of Twort(4(^) and of 

 Revis(35) may be noted. The former found that certain coli- 

 typhosus organisms were able to acquire the power of fermenting 

 certain sugars if grown in them for a sufficiently long time, the 

 change taking place slowly. In this manner he modified 



