51 



The results show that the infestation is sligfhtly less on some 

 varieties than on others. These varieties are, however, too closely 

 related racially, to give striking- differences, and the experiments 

 are beingf continued with other varieties of Beans. 



Further investij^^ations are in hand dealing with the effect of 

 the nianurial treatment of crops on the degree of the infestation of 

 j:)lants by aphids; the relations between the varying constitution of 

 the cell sap of plants, the food of aphids, and the infestation c»f 

 plants by them, and the working of the stylets in relation to the 

 cells of plant tissues. 



XXX II. W. B. Brieklev. " Some Concepts in Mycology 



— an attempt at Synthesis/' Trans. British 

 Mycological Societv, 1919. Vol. VI. (part ii.). 

 204-235. 



The paper is divided into two parts which, however, are 

 mutually dependent — the species concept and the concept of the 

 educability of fungi. In the former the thesis is maintained that 

 the morphological characters of an organism are a function of the 

 particular genotype and the environmental conditions, and that the 

 phenotypes of different organisms converge or diverge in constant 

 and definite relation to the physico-chemical factors of the environ- 

 ment. Thus morphological characters are no true criterion of 

 specificity. It is further maintained that the only exact method of 

 species creation and specific determination is by means of quantita- 

 tive physiological data derived from pure cultural treatment under 

 standardised physico-chemical conditions. In the second part 

 the thesis is put forward that the genotypes of ** pure lines " of 

 bacteria and fungi are constant and ineducable, and that genotype 

 changes whi(^h ha\e been described are better interpreted in terms 

 of modification, of the selection of strains from a population, cf 

 stages in a complex life-cycle, or of segregation from a genetically 

 impure ancestor. 



XXXIII. W. B. Brierlev. " On a Form of Botrytis 



cinerea, with Colourless Sclerotia." Phil. 

 Trans. Roval Societv of London, 1920. Series 

 B. Vol. 210. 83-114. 



The fungus, Botrytis cinerea, produces black sclerotia, but in 

 a single spore pedigree culture a colourless sclerotium was formed, 

 which gave rise to a strain having colourless sclerotia. This 

 character proved to be constant. The origin and relationships of 

 this new strain are examined and a comparison made of the mor- 

 phology and physiology of the colourless derivative with the 

 parent. It is shown that the only apparent character in w^hich the 

 two strains differ is in the absence of pigment in the sclerotial skin. 



The nature of the loss of colour is considered in relation to the 

 biochemistry and genetics of albinism. The significance of the 

 colourless form is discussed and the hypothesis brought forward 

 that this and other genotypic changes among fungi are better inter- 

 preted in terms of segregation from a genetically impure parent 

 than as true mutations. The possibilities of genetic contamina- 

 tion in sexual and asexual fungi are considered. 



