684 THE AMERICAN NATURALIST. [Vou XXXIIL. 
constancy is to be expected in living organisms in general; they 
cannot be made to revert. as far as we know, and I therefore 
fail to see why they should not be admitted to be scientific 
species. The same is true of the physiological species of 
bacteria, meaning, of course, those which have been well studied, 
and excluding the mass of ill-described and ill-known forms 
which abound in bacteriological writings. When a race has 
become so constant that it no longer reverts, and we cannot tell 
from what species it came, it is no longer a race, but a species. 
It may be objected, however, that both bacteria and Saccha- 
romycetes differ from ordinary plants in a most important 
respect, víz., that there is a complete absence of sexuality and 
the reproduction is purely vegetative. There are a few bota- 
nists, to be sure, who think that there is a form of sexuality in 
Saccharomycetes, but botanical opinion at present is so over- 
whelmingly on the other side that to call the question an open 
one would require an explanation which time will not permit. 
It may be urged that in plants in which sexuality is wanting 
we have no right to speak of a perennial succession of like 
individuals, for, it may be claimed, succession means by sexual 
generation only. This interpretation is very convenient if one 
wishes to ignore forms like bacteria and Saccharomycetes in 
the consideration of the question of species, but to exclude 
them on this ground is somewhat dangerous unless we are 
prepared to admit, offhand, that species are purely artificial. 
It is the custom to speak of bacteria and Saccharomycetes 
as degenerate forms. What is meant by this expression is not 
plain, unless it means that, arising presumably from plants in 
which sexuality was present, they have become non-sexual. 
Undoubtedly sexuality is the rule in nature, but it should be 
borne in mind that it is not universal. I do not refer here to 
fungi like Ascomycetes and Basidiomycetes, which, accepting 
the hasty conclusions of the Brefeld school, have been, even by 
a good many of our own botanists, included in the limbo of 
non-sexual degenerate forms, from which more recent observers 
are gradually rescuing them. I refer rather to species like 
Rhodymenia palmata, one of the commonest red seaweeds of 
the. North Atlantic, in which, so far, nothing has been discov- 
