174 BOTANICAL GAZETTE [MARCH 
contradiction with the other hypotheses. If we accept these views, 
all reasons for supposing a correlation between the splitting phe- 
nomenon and the mutability would lose their value, and this 
latter process would come much nearer to the corresponding 
changes in O. biennis and allied species. The hypothesis, although 
resting on too large a number of suppositions, would in some sense 
be a support for the theory of mutation, since it is evidently impos- 
sible that these presumed qualities; which are incompatible with 
life, could have evolved slowly on the ground of their utility in the 
struggle for existence. Moreover, the hypothesis has no direct 
bearing on the observed phenomena of mutation, and the fact that 
in O. biennis such empty seeds are wholly or almost wholly absent 
proves beyond doubt that mutability may be independent of 
them. Thus the hypothesis of RENNER emphasizes the importance 
of a study of the mutation phenomena in O. biennis, in contra- 
distinction to those in O. Lamarckiana, at least for the present, 
until facts are available to appreciate the correctness of his views. 
Obviously the hypothesis that O. Lamarckiana might be a 
hybrid, whilst O. biennis is not, can in no way account for the 
phenomena of mutation which are common to both of these species. 
For this reason it seems important to describe the degree of muta- 
bility as it has been observed, up to this time, in O. biennis, which 
is, next to O. Lamarckiana, the most suitable species for this kind 
of research. The mutations in the other forms seem to be far 
more rare, and therefore require many more thousands of indi- 
viduals for a statistical study or for experiments upon their causes. 
Besides the assumption that O. Lamarckiana might be a hybrid, 
some authors have recently pointed out that hybridism may be one 
of the chief ways in which species are produced in nature, especially 
in the larger or so called polymorphous genera. LINNAEUS was 
the first to propose this hypothesis, at the time when the number of 
discovered forms was growing so fast as to make it almost impossible 
to assume a separate creation for every one of them. I have not 
the least doubt that Linnargus and his followers were right in this 
point, and that many wild species have been produced by the 
sexual combination of the characters of their allies. How great 
a réle this kind of hybridization or of the recombination of char- 
