(a) selection.
(b) hybridizing.
(c) budding and grafting.
Laboratory demonstration.—From charts to illustrate how human characteristics may be inherited.
heredity and eugenics
Heredity and what it Means.—As I look over the faces of the boys in my class I notice that each boy seems to be more or less like each other boy in the class; he has a head, body, arms, and legs, and even in minor ways he resembles each of the other boys in the room. Moreover, if I should ask him I have no doubt but that he would tell me that he resembled in many respects his mother or father. Likewise if I should ask his parents whom he resembled, they would say, "I can see his grandmother or his grandfather in him."
This wonderful force which causes the likeness of the child to its parents and to their parents we call heredity. Heredity causes the plants as well as animals to be like their parents. If we trace the workings of heredity in our own individual case, we will probably find that we are molded like our ancestors not only in physical characteristics but in mental qualities as well. The ability to play the piano or to paint is probably as much a case of inheritance as the color of our eyes or the shape of our nose. We are a complex of physical and mental characters, received in part from all our ancestors.
Variations in the Catalpa caterpillar. (Photographed, natural size, by Davison.)
Variation.—But I notice another thing; no boy in the class before me is exactly like any other boy, even twins having minute differences. In this wonderful mold of nature each one of us tends to be slightly different from his or her parents. Each plant, each animal, varies to a greater or lesser degree from its immediate ancestors and may vary to a very great degree. This factor in the lives of plants and animals is called variation. Heredity and variation are the cornerstones on which all the work in the improvement of plants and animals, including man himself, are built.