Prop′aga′tion, as a natural process among wild plants, is accomplished by the various methods of scattering spores (q. v.) and seeds (see Seed-Dispersal), through parts of plants, as buds and twigs, breaking off and taking root or even by the entire plant being carried by the wind, as such “tumble-weeds” as the Russian thistle and pigweed. Other means of propagation are runners and branches that take root at their joints or tips, as the strawberry and raspberry. Many plants spread only too effectively through shoots sent up by their roots and underground stems, as the silver-leaf poplar and Canadian thistle. But in the horticultural sense propagation refers to a group of artificial processes, as budding, grafting and layering (see these headings), the planting of seeds, bulbs, tubers, cuttings etc. or the transplanting of young plants (see Hotbed). The reproduction of plants by other means than from the seed is spoken of as vegetative propagation, and is used to keep some desirable characteristic that will not breed “true” in seedlings, as in fruit-trees. (See Grafting.) For the manner in which new varieties are produced see Plant-Breeding.
