144 BROOKLYN BOTANIC GARDEN MEMOIRS 
these facts together with that mentioned above regarding the in- 
constancy of the results obtained from planting the seed of self-sterile 
plants, may be interpreted by the assumption that he was dealing 
entirely with fluctuations in all of the five species investigated. These 
species genetically were wholly self-sterile. The tendency toward 
self-fertility was due to conditions. In other words, these plants 
genetically self-sterile needed conditions conducive to a fine healthy 
growth to bring out their self-sterility. In the lower temperature of 
England, at a time of decline (the last of the flowering season), they 
became phenotypically somewhat self-fertile. In the light of my own 
experiences, I believe we can reconstruct a picture of Darwin’s experi- 
ments on Reseda odorata with considerable confidence. He isolated 
the plants that he desired to test under nets; then came pressure of 
other work, and the data were not collected until the plants had ceased 
flowering. At that time capsules were found beneath the nets, and 
this seemed to prove at least a partial self-fertility. But instead of 
this procedure, suppose that successive self-pollinations had been 
made throughout the season. The presumption is that the plants 
would have been declared to be self-sterile with the same remark 
added which he jotted down in the case of Abutilon darwint, viz., 
they ‘‘became moderately self-fertile late in their flowering season.” 
Again, Darwin found no cross-sterility in the plants tested, and 
concluded that a self-sterile plant can be fertilized with the pollen 
of any one of a thousand or ten thousand individuals of the same spe- 
cies. Such a conclusion was less cautious than was Darwin’s wont for 
it was made from a total personal experience of some twenty-odd cross- 
matings only, unless his records are extremely incomplete. Indeed 
this conclusion must have been somewhat of a surprise to himself 
since he states that ‘“‘it is obvious impossible that the sexual organs 
and elements of every individual can have been specialized with respect 
to every other individual.’’ He surmounted this difficulty by assum- 
ing that the sexual elements of each plant differ slightly in the same 
manner as their external characteristics, and that this slight difference 
is sufficient to excite the mutual action of the sex elements necessary 
in order to have fertilization ensue. The kernel in this conclusion, 
that differences in the reproductive systems of two self-sterile plants 
are necessary in order to promote cross-fertilization, is so similar to 
that to which the writer has been forced after seven years of rather 
intensive work as to be uncanny, for it seems to have been reached 
in spite of rather than because of the data at hand. This feeling of 
surprise at Darwin’s clairvoyancy may seem affected, since he was 
usually in advance of his time, but it is a fact perhaps worth men- 
tioning as a confession of omission that the writer reached his con- 
