226 Transactions British Mycological Society. 



case the action may not be reversed for there is now no sub- 

 ordinate strain to select out. This explanation is probably 

 common to many of those results where the change is permanent 

 — that is the property once acquired by the race is never lost. 

 This is well illustrated by an experiment of Horiuchi(i6), who 

 relates that he had in his possession a highly virulent, densely 

 capsulated strain of the micrococcus tetragenus, which resisted 

 phagocytosis almost entirely and killed guinea pigs in a dose 

 of 100 organisms. When this was grown for a number of days 

 on rather dry agar it lost its capsule-forming power permanently, 

 became readily subject to phagocytosis, and did not affect 

 guinea pigs even in doses of 1,000,000,000 organisms. 



In Case III the non-fermenting organism is found to be abso- 

 lutely ineducable by any treatment whatsoever. This is due to 

 the fact that it is really a pure species, and not a population 

 out of which a particular subordinate strain may be selected. 



Case IV is the reversal of Case II. In the latter a character 

 is developed by the selection from a population of a subordinate 

 component possessing that character. Iri the former the 

 population is originally fermentative but loses that capacity 

 because the subordinate species which finally becomes dominant 

 cannot form the necessary enzymes. As no individuals of 

 the originally dominant species remain, the population becomes 

 a pure line which is constant. 



Case V corresponds to Case III, but the fermenting power 

 is retained under all treatments. 



In these five conditions and multiples of them, all possible 

 educative phenomena may be included; and except in those 

 investigations where the organism has been initially derived 

 from a single individual, and subsequently the most rigid 

 precautions adopted to eliminate possibility of contamination, 

 it is more consonant with principles of scientific methodology 

 to adopt a hypothesis stated in terms of the selection of existing 

 species from a population, than a hypothesis which requires 

 the introduction of such a new and fundamentally destructive 

 idea as that of the fluidity of species. 



That two or more fungal or bacterial species may grow 

 together so harmoniously that the mixed nature of the culture 

 cannot be detected save by the most scrupulous attention to 

 a special technique is a fact that as yet is hardly receiving due 

 recognition. Under most environmental conditions the two 

 or more organisms "harmonise" perfectly in their growth 

 but under the influence of certain other environmental factors 

 they may "disharmonise" or shew characteristic divergencies, 

 when the mixed character of the population becomes evident. 

 This is the case with certain species of the "Linneon" Botrytis 



