Some Concepts in Mycology. Williaui B. Brierley. 221 



dysentery bacteria (Kriise and Flexner strains) so that they 

 were able to ferment saccharose : and he was able to train 

 B. typhosus to ferment lactose and dulcite, the power being 

 retained permanently. 



Revis(33) investigated certain coli-typhosus organisms which 

 produce both acid and gas when cultured in peptone-broth 

 plus certain sugars or polyhydric alcohols, and was able 

 gradually to acclimate these organisms to a medium containing 

 o-i per cent, of malachite green. When returned to the 

 original medium the organisms were found to have lost the 

 power of producing gas though they could still form acid. 



The best known case of fungal education is that described by 

 Massee(25). Following out certain indications given in one of 

 Miyoshi's(27) experiments Massee sowed spores of Tricothecium 

 candidum on leaves injected with sugar solution and from the 

 growths thus obtained re-inoculated other injected leaves. 

 This was done for several generations of the fungus, after 

 which spores from the last growth were sown on normal leaves 

 and infection obtained. "This means that after twelve genera- 

 tions of the fungus, educated to grow in living Begonia by 

 means of chemotactic substance — a solution of cane sugar — 

 the faculty of parasitism had been acquired for this particular 

 host plant." "The period of time required in this series of 

 experiments for the conversion of a saprophytic fungus into a 

 true parasite was twelve weeks, and the number of generations of 

 the fungus amounted to sixteen." " By similar means a parasitic 

 fungus can be induced to become parasitic on a new host." 



The changes illustrated in the foregoing paragraphs are 

 induced or educative changes of which the results were trans- 

 mitted to offspring. The change is therefore one of genetic 

 constitution. The difference between the two categories is 

 very clearly expressed by Dobell(8) as follows: "Let us suppose 

 that a given Bacillus is coloured red under normal conditions. 

 By growing it and its offspring upon a new medium they become 

 — let us suppose — colourless. If the organisms and their 

 descendants when transplanted again into the original medium 

 are again found to be red, then the change (loss of colour) is a 

 modification ; if, on the other hand, they are found to be now 

 permanently colourless, then the change is a mutation." It is 

 the induced mutation, the permanent change in genetic con- 

 stitution brought about under controlled conditions and at 

 will by certain educative treatment, which is the subject of 

 this consideration. 



The possibility of such facile genetic change carries certain 

 corollaries, which perhaps have not been envisaged with 

 sufficient clearness or reasoned to their logical conclusions, by 



