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! Many of our most 
ornamental flowers, especially varieties of Canna, Ameryllis, and 
Gladiolus, 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 
1S8ee Yearbook of the Department of Agriculture, 1904. 
2 See L, H. Bailey, Plant-Breeding, Lecture III. The Macmillan Company, 
New York, 
