A large number of horticultural varieties have been developed by hybridization, some of which have a variegated foliage.
The tobacco flower is fortunately perfectly self-fertile, and by enclosing the flowers of selected plants in paper bags, so as to exclude all possibility of hybridization, progeny true to the type of the mother plant can be obtained.
From these, or rather from some of these, by cultivation and hybridization, have arisen the very numerous modern varieties.
Some of the most interesting results and many of the gardener's greatest triumphs have been obtained by hybridization, i.e.
The occurrence of hybrids in nature explains the difficulty experienced by botanists in deciding on what is a species, and the widely different limitations of the term adopted by different observers in the case of willows, roses, brambles, &c. The artificial process is practically the same in hybridization as in cross-fertilization, but usually requires more care.