This process of self-fertilization is the usual method, and no doubt keeps the variety true or unmixed; but the occasional presence of varieties in a wheat-field shows that cross-fertilization is sometimes secured.
It is obvious that hybridization differs more in degree than in kind from cross-fertilization.
Modern experiments in cross-fertilization in Lancashire by the Garton Brothers have evolved the most extraordinary "sports," showing, it is claimed, that the plant has probably passed through stages of which until the present day there had been no conception.
This coronet forms the most conspicuous and beautiful part of the flower of many species, and consists of outgrowths from the tube formed subsequently to the other parts, and having little morphological significance, but being physiologically useful in favouring the cross-fertilization of the flower by means of insects.
The easiest to cultivate, and experiments have consequently been made in cross-fertilization and grafting with the view of giving vigour of growth to delicate trees yielding a large amount of alkaloid or of increasing the yield in strong-growing trees affording but little quinine.
Thus the species' of wheat are usually selffertilized, but cross-fertilization is possible since the glumes are open above, the stigmas project laterally, and the anthers empty only about one-third of their pollen in their own flower and the rest into the air.
In 1799 an Englishman, Thomas Andrew Knight, after experiments on the cross-fertilization of cultivated plants, formulated the conclusion that no plant fertilizes itself through many generations.
The stamens of the wheat plant may frequently be seen protruding beyond the glumes, and their position might lead to the inference that cross-fertilization was the rule; but on closer examination it will be found that the anthers are empty or nearly so, and that they are not protruded till after they have deposited the pollen upon the stigma.
18, and Paniceae), and in these the male flower of a spikelet always blooms later than the hermaphrodite, so that its pollen can only effect cross-fertilization upon other spikelets in the same or another plant.
The greatest difference of opinion exists among botanists as to their number and the bounds to be assigned to each; and the cross-fertilization that takes place between the species intensifies the difficulty.