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 

 j genetically self-sterile needed conditions conducive to a fine healthy 

 1 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 danvinii, viz., 

 they "became moderately self-fertile Jlate in__thej.r Jioi^ering 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 difificulty 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 d i fference s in the re^j roductoeL systems of two s e lf-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 reachtd his con- 



