190 INTRODUCTION TO BOTANY 



habit of growth, and form of root, stem, or leaf (fig. 161). 

 They may show much variation in the flowers or in the fruit 

 (fig. 160). The physiological characters of the seedlings may 

 vary greatly ; that is, they may have very different periods 

 of maturity and of hardiness in resisting drought, frost, or 

 disease. If any of the characters of the hybrid are highly de- 

 sirable, the breeder will try to perpetuate the type. If he is 

 dealing with a plant like the potato or the bulb-bearing plants, 

 which can be propagated by planting the tubers, bulbs, or simi- 

 lar parts, the effort to introduce the new variety will probably 

 succeed ; and it is not difficult to propagate new varieties of 

 grapes by cuttings, and apples, pears, quinces, peaches, plums, 

 and cherries by grafting or budding ; but in the case of plants 

 which must be grown from the seed the perpetuation of hybrid 

 varieties is often difficult or impossible. Sometimes the 'seed 

 of the hybrid seedling cannot be made to grow, and some- 

 times the plants will not come true from the seed, so that 

 the promising hybrid variety is represented only by one plant, 

 which leaves no descendants like itself. Professor L. H. Bailey, 

 one of the highest authorities on plant breeding, has by cross- 

 ing obtained about a thousand wholly new types of pumpkins 

 and squashes, and never succeeded in perpetuating a single one. 



179. Instances of successful hybrids. A few successful varie- 

 ties of wheat and corn are the result of hybridization, and more 

 may be expected in the future. Many good grapes are known 

 to be hybrids, and so are probably a few of the best, like the 

 Delaware and Catawba. Some good blackberries and many 

 excellent plums have been obtained by hybridization. Citrous 

 fruits have been successfully hybridized. 1 Many of our most 

 ornamental flowers, especially varieties of Canna, Amaryllis, and 

 Grladiolus, together with great numbers of orchids, are hybrids. 



180. Some rules for plant breeding. 2 Neither the science 

 nor the art of plant breeding can be taught wholly from 



1 See Yearbook of the Department of Agriculture, 1904. 



2 See L. H. Bailey, Plant-Breeding, Lecture III. The Macmillan Company, 

 New York. 



