No. 381.] THE CONCEPTION OF SPECIES. 683 
On the other hand, no one has yet succeeded beyond a doubt 
in making the Saccharomycetes proper revert to a higher ances- 
tral form. I say beyond a doubt, because the observations of 
Juhler, Joergensen, and Johan-Olsen, on the relation of Asper- 
gillus, Sterigmatocystis, and Dematium, to Saccharomycetes, 
have not been confirmed by other equally good observers, as 
Kloecker and Schioenning ; and, for the present at least, we 
must regard the observations of Joergensen and Johan-Olsen 
as affording still other instances of the fact that under proper 
conditions the germinating spores of many fungi produce bodies 
like Saccharomycetes, while they do not show conclusively that 
forms recognized by specialists as genuine Saccharomycetes can 
be transformed into fungi of other orders. They do, however, 
show that the views of Brefeld that the Saccharomycetes are 
derived from Ustilaginaceze could, at the best, be only partially 
true. 
Let us return to the question as to whether or not species of 
the Saccharomycetes, as defined by Hansen for instance, should 
be allowed to be called species in the proper sense of the word. 
Of course no one supposes that they have always existed in 
their present form, and, although we have no exact knowledge 
of the ancestors of the present species, we naturally suppose 
that they were derived from some other higher fungi, as the 
expression goes. Whether derived from one particular order 
of fungi or from several different orders, the species as we now 
see them seem to be constant in the sense that that word must 
be used in speaking of species of any group of plants. The 
shape of the cells in any given species, although variable to’ 
some extent, is constant within definable limits, and, although 
they have periods of rest and periods of activity, their physio- 
logical action seems to be the same under similar conditions. 
We might be justified, it seems to me, in regarding as races 
the Saccharomycetes-like forms which result from the germina- 
tion of spores of higher fungi, provided they continued to live 
an independent existence for a time and were not, as is more 
likely to be the case, merely accidental conditions depending on 
unusual or unfavorable conditions of germination, but the 
Saccharomycetes in the limited sense are constant, as far as 
