PLANT BREEDING 507 



sprouting from the eyes of the new kinds of tubers. In raising 

 seedless varieties of fruit, vegetative propagation is the only 

 possible procedure. The breeder may use grafting for trees, 

 and cuttings, tubers, bulbs, or layering for smaller plants. For 

 many of the common crop plants, such as grains, the bean 

 family, radishes, the cucumber family, and others, the preserva- 

 tion of hybrids through vegetative multiplication is impossible 

 because these plants are annuals and have no parts from which 

 new individuals can grow except the seeds. New varieties that 

 arise from hybridizing are thus likely to get lost. 



370. Heredity. How is it that the characters of organisms 

 are so regularly repeated in their offspring? And how is it that 

 in spite of the close resemblance between parents and offspring 

 these are never exactly alike in every point? All the specula- 

 tion on these questions led to nothing until some experiments 

 were undertaken. The results of some of these experiments 

 have helped to solve in part the practical problem of keeping de- 

 sirable variations that result from hybridizing. The first sys- 

 tematic experiments of. which we have any record were those of 

 Gregor Mendel (182 2-1884), an Austrian monk. Mendel had 

 long puzzled his mind over the great amount of variation among 

 his garden peas. There were tall plants and short ones, plants 

 with white flowers and plants with colored flowers, with yellow 

 seeds and with green seeds, with smooth seeds and with wrinkled 

 seeds. All in all he studied seven different pairs of contrasting 

 characters in the pea plants. He noticed further that a given 

 plant might have any combination of single members of these 

 seven pairs. Thus, a hairy plant might be tall or it might be 

 short ; a tall hairy plant might have white flowers or pink 

 flowers ; it might have yellow seeds or green seeds ; and so on. 



371. Menders experiments. Fixing his thought on a single 

 character at a time instead of trying to think of the variety as a 

 whole, Mendel crossed garden-pea plants that differed from each 

 other. He crossed green-seeded with yellow-seeded, tall ones 

 with short ones, hairy ones with bald ones, and so on for his 

 seven pairs of characters. Moreover, in all his experiment? he 



