How Trees Are Multiplied — Part 4

To bear the Medlar and the Pear

He bids the rustic Plum to rear

A noble Trunk and be a Peach."

The modern rule of "seed on seed and pit on pit' is embodied in this account. The species named are all in the same botanical family at least. Plums are budded upon peach stocks in the South. Peach-rooted trees thrive better in the hot, sandy soil than plum-rooted trees do. In the Northern States peaches are budded on plum stocks which are hardier in the native kinds. Crab apples, native to various regions, prove good stocks for introduced varieties of apples.

The limits of grafting are not very well defined yet. The safest and most practicable method is to inter-graft varieties of one species. Remoter relationships admit of union sometimes, as the peach and plum, which are of different species; by some authorities these are considered of different genera. The mountain ash has served as a stock for apples--again, two different genera. But these instances are plainly beyond safe limits.

The origination of new varieties by hybridisation is an entirely different subject. Its variations come through the seeds. Here the pollen, scattered in various ways when plants blossom, falls on the pistils of flowers somewhat indiscriminately. Especially is this true of wind-fertilised flowers which produce pollen in abundance and of a dry, powdery sort. The pollen lies inert on the stigmas of alien species. It fertilises those of its own kind. There are intermediate varietal relationship and very closely related species in certain families. In these cases natural crosses occur, flowers being fertilised by pollen of another species. Seeds thus set produce hybrid plants, new kinds having characters of their two parents. Thus the species of willows are hopelessly intermixed. Natural crosses between oaks are frequently discernible in the woods. The white oak crosses with several species in its own (annual) group. The biennial or black oaks also intercross among themselves. But black and white oaks do not cross.

Artificial crosses are frequently made by plant breeders for scientific and economic reasons. Some of the best horticultural varieties of fruits and flowers are artificial hybrids. Among these are the Kieffer pear, the wild goose plum, and various roses, grapes, begonias, cannas and pelargoniums. Hybrids are propagated by division.