EAST: INTERCROSSES BETWEEN SELF-STERILE PLANTS 143 
very last of the flowering season? self-sterile plants may sometimes 
become somewhat self-fertile. 
Darwin’s (1876, p. 346) general conclusions are as follows: 
‘Finally, the most interesting point in regard to self-sterile plants 
is the evidence which they afford of the advantage, or rather the 
necessity, of some degree or kind of differentiation in the sexual 
elements, in order that they should unite and give birth to a new being. 
It was ascertained that the five plants of Reseda odorata which were 
selected by chance could be perfectly fertilised by pollen taken from 
any one of them, but not by their own pollen; and a few additional 
trials were made with some other individuals, which I have not 
thought worth recording. So again, Hildebrand and Fritz Miiller 
frequently speak of self-sterile plants being fertile with the pollen of 
any other individual; and if there had been any exception to the 
rule, these could hardly have escaped their observation and my own. 
We may therefore confidently assert that a self-sterile plant can be 
fertilised by the pollen of any one out of a thousand or ten thousand 
individuals of the same species, but not by its own. Now it is obvi- 
ously impossible that the sexual organs and elements of every indi- 
vidual can have been specialised with respect to every other indi- 
vidual. But there is no difficulty in believing that the sexual elements 
of each differ slightly in the same diversified manner as do their 
external characters; and it has often been remarked that no two 
individuals are absolutely alike. Therefore we can hardly avoid the 
conclusion that differences of an analogous and indefinite nature in 
the reproductive system are sufficient to excite the mutual action of 
the sexual elements, and that unless there be such differentiation 
fertility fails.” 
One cannot but admire these inductions Darwin has so cleverly 
drawn from such meager data, nevertheless one cannot accept them 
today just as they stand. The reasons for this statement will be 
seen more clearly when our own data have been presented, but a brief 
can be submitted with only the support of the work known to Darwin. 
In the first place, the seemingly contradictory results that were 
obtained in the experiments on Reseda odorata are not necessarily con- 
fusing. As reported, self-sterile plants produced varying ratios of 
self-sterile and self-fertile plants. Unfortunately, the progeny of the 
self-fertile plants was not followed. If it has been, the problem might 
have been more easily solved, for, in all probability, the daughter 
plants would have been self-sterile. It is my own belief, however, 
that the answer can be read in the casual remarks dropped by Darwin 
in the midst of his careful descriptions, remarks to which he paid little 
attention. Darwin found that both Eschscholtzia california and 
Abutilon darwinti, though self-sterile in Brazil tended to become self- 
fertile in England,—especially late in the flowering season. Now 
2 Cf. Darwin’s observation on Abutilon darwinu. 
11 
