178 BOTANICAL GAZETTE [ARCH 
are sterile. Aneztffia, Xylopleurum, and Lavauxia have some rudi- 
mentary ovules as well as sterile pollen grains (10-50 per cent). 
In the genus Oenothera, with the subgenera Onagra, Euoenothera, 
and Anogra, the percentage of sterility is about 50 per cent in the 
ovary as well as in the anthers. In the first group about 40 species 
were studied, in the second 30, in the third 1o, and in the last 
40, making together about 120 species. If in the last three groups 
some species were pure, and devoid of sterile sexual cells, they 
would no doubt have been discovered, and the supposition that 
the remainder might be considered as their hybrids would have 
found support. But this was not the case, and if we wish to ascribe 
the presence of all these sterile sexual cells to ancestral crosses, the 
crosses must be supposed to have taken place, or at least to have 
begun, among the ancestors of the whole family, with the exception 
of the Lopezieae, the Jussieueae, and the Epilobieae. It seems 
hard to have to suppose that the whole pedigree of the Xylo- 
pleurinae, the Clarkiinae, and the Oenotherinae should have had to 
go through the development of partial sterility in order to produce 
the present mutability of Oenothera Lamarckiana and half a dozen 
or perhaps even a dozen of its nearest allies. 
The second main supposition, namely that hybridian might 
be a cause of mutability, is dealt with by JeFrREy in a particular _ 
way. He assumes “that there is every reason to suppose that it 
has been an agency of great importance in multiplying species, 
although it is logically inconceivable in the present state of our 
biological knowledge that it could have presided at their origin.” 
The first of these two alternatives represents, so far as I can see, 
a conviction which is at least very widely spread among biologists 
ever since the time of LinnaEvus. It by no means contradicts the 
theory of natural selection,. nor that of mutation, nor any other 
evolutionary principle. It has no obvious reference to the phe- 
nomena observed in the evening primroses, since with them the 
production of new forms takes place in pure lines of a species which 
has come down to us unchanged during at least a century, since 
the time MicHavx discovered it in the United States and sent it to 
Europe. At least there is no direct recombination of characters 
6 The probable origin of Oenothera Lamarckiana. Bor. Gaz. §7:345-360- 1914; 
see pl. rg. 
