No. 381.] THE CONCEPTION OF SPECIES. 681 
he calls his species on physiological characters, including in that 
term zymotic and pathological action. By botanists, who are 
not specially bacteriologists, the so-called species of bacteria 
are not admitted to be species in the proper sense. Whether 
scientifically considered they are not as legitimately species as 
what are called species in speaking of the higher plants, is a 
very pertinent question. Any definition of species, to be scien- 
tifically accurate, must in its essential points apply to all plants 
and all animals; and if a species of flowering plant is a peren- 
nial succession of like individuals, it is hard to see why in 
bacteria a perennial succession of like individuals does not 
also constitute a species. That the individuals in bacteria are 
very different from the individuals in flowering plants is cer- 
tainly true, but that does not affect the question of the validity 
of the species in the former. As far as the perpetuation of 
morphological likeness of the individuals is concerned, there is 
no doubt that it is, to say the least, as complete in bacteria as 
in flowering plants, and the physiological constancy has been 
shown by competent observers to persist in some cases for 
hundreds of generations. That these many generations have 
been produced in months rather than in hundreds of years does 
not, it seems to me, affect the case. 
When, therefore, the botanist denies that physiological 
species are properly species, he is practically admitting that 
his own definition, the perennial succession of like individuals, 
is used by him in a special sense, and he does not seem to be 
aware that species as he limits them are artificial and not natu- 
ral. The belief that species should be based on morphological 
rather than physiological characters rests on the assumption 
that the former are more likely to be inherited, and thus show 
the ancestry, while the latter are more likely to be the result of 
the temporary attempts of the organism to adapt itself to the 
environment. It is perhaps a question whether the grounds for 
this belief are as valid as has been supposed. We readily see 
morphological characters which have been inherited, but it is 
usually only by accident or experiment that we recognize the 
Physiological or pathological qualities. 
Let us turn for a moment from bacteria to Saccharomycetes, 
