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Nov 18/62/ The fact proved by such a mass of evidence that crossing two individuals long distinct, & probably longer kept distinct the better, adds to vigour & fertility of offspring, shows that there must be some excessively slight difference in pollen of every individual of same species. — Under unnatural conditions we find that the pollen gets so wonderfully altered (though effectual in itself) that as in Lobelia, Potato, Passiflora — Crinum &c the flower is quite sterile with its own pollen & requires that of another.

This throws flood of light on dimorphism & makes it not improbable (seeing the individual difference of pollen) that sterility may be selected to keep vars. distinct.