We are reminded by this latter fact of the extraordinary cases of Hippeastrum, Passiflora, etc.

, which seed much more freely when fertilised with the pollen of a distinct species than when fertilised with pollen from the same plant.

We thus see that, although there is a clear and great difference between the mere adhesion of grafted stocks and the union of the male and female elements in the act of reproduction, yet that there is a rude degree of parallelism in the results of grafting and of crossing distinct species.