It is only when plants of two distinct kinds are crossed that the result is called a hybrid; for example, a blackjack oak on a white oak, an apple on a pear. If the parent plants are closely related, for example, two kinds of apples, the resulting plant is known simply as a cross.
Hybrids and crosses are valuable in that they usually differ from both parents and yet combine some qualities of each.
Fig. 38. Orange Blossom prepared for crossing
First, bud; second, anthers unremoved; third, anthers removed
Fig. 39. Tomato Blossom ready to cross
First, bud; second, anthers unremoved; third, anthers removed
Fig. 40.
First, blossom bagged to keep out stray pollen; second, fruit bagged for protection
They often leave off some of the qualities of the parent plants and at other times have such qualities more markedly than did their parents. Thus they often produce an interesting new kind of plant. Sometimes we are able by hybridization to combine in one plant the good qualities of two other plants and thus make a great advance in agriculture. The new forms brought about by hybridization may be fixed, or made permanent, by such selection as is mentioned in Section XVIII. Hybridization is of great aid in originating new plants.
It often happens that a plant will be more fruitful when pollinated by one variety than by some other variety. This is well illustrated in Fig. 41. A fruit-grower or farmer should know much about these subjects before selecting varieties for his orchard, vineyard, etc.