Of eight pairs of Lupinus luteus, all but two of the crossed were taller; of eight pairs of Beta vulgaris all but one; and of fifteen pairs of Zea mays all but two were taller.  Of fifteen pairs of Limnanthes douglasii, and of seven pairs of Lactuca sativa, every single crossed plant was taller than its self-fertilised opponent.  It should also be observed that in these experiments no particular care was taken to cross-fertilise the flowers immediately after their expansion; it is therefore almost certain that in many of these cases some pollen from the same flower will have already fallen on and acted on the stigma.

There can hardly be a doubt that several other species of which the crossed seedlings are more vigorous than the self-fertilised, as shown in Tables 7/A, 7/B and 7/C, besides the above fifteen, must have received their own pollen and that from another plant at nearly the same time; and if so, the same remarks as those just given are applicable to them.  Scarcely any result from my experiments has surprised me so much as this of the prepotency of pollen from a distinct individual over each plant’s own pollen, as proved by the greater constitutional vigour of the crossed seedlings.  The evidence of prepotency is here deduced from the comparative growth of the two lots of seedlings; but we have similar evidence in many cases from the much greater fertility of the non-castrated flowers on the mother-plant, when these received at the same time their own pollen and that from a distinct plant, in comparison with the flowers which received only their own pollen.

From the various facts now given on the spontaneous intercrossing of varieties growing near together, and on the effects of cross-fertilising flowers which are self-fertile and have not been castrated, we may conclude that pollen brought by insects or by the wind from a distinct plant will generally prevent the action of pollen from the same flower, even though it may have been applied some time before; and thus the intercrossing of plants in a state of nature will be greatly favoured or ensured.

The case of a great tree covered with innumerable hermaphrodite flowers seems at first sight strongly opposed to the belief in the frequency of intercrosses between distinct individuals.  The flowers which grow on the opposite sides of such a tree will have been exposed to somewhat different conditions, and a cross between them may perhaps be in some degree beneficial; but it is not probable that it would be nearly so beneficial as a cross between flowers on distinct trees, as we may infer from the inefficiency of pollen taken from plants which have been propagated from the same stock, though growing on separate roots.  The number of bees which frequent certain kinds of trees when in full flower is very great, and they may be seen flying from tree to tree more frequently than might have been expected.  Nevertheless, if we consider how numerous are the flowers, for instance,