(3) rtility.—ilybridity has great practical utility in agriculture. Many varieties of our domesticated plants have arisen from artificial hybrids. The first generation of hybrids usually gives few results, but great. variations continue to appear in subsequent generations. Thu., when two species of hybrid foliaceous; plants are crossed, the leaves of the second or third genera tion are often highly variable. This great varia bility. on the other hand, renders any favorable variation liable to he lost unless great pains are taken to fix the desired quality by in and-in breeding. or unless the quality can he reproduced vegetatively—i.e. by cuttings and grafts. The diminished fertility of sonic hybrids is agricul turally advantageous in the ease of plants that tan be reproduced vegetatively. Sonic of the advantageous results of hybridization are as fol lows: (a) lnereas•d Size and Vigor. The hybrid between the walnut and the California black walnut is of exceptional value, "for it grows twice as fast as the combined growth of both parents. The wood is very compact, with lustrous silky grain," etc. Another hybrid of the black walnut and the California black walnut produces fruit of much larger size than that of either parent. These are illustrations of a com mon result of hybridization—increased size and (b) Increased llardiness. The production of hardy races of plants is very important, be cause it carries farther north the limits of ngri culture and increase-, the area of eultivation. Every Jew years the orange and lemon trees of the Gulf States and California are greatly dam aged by freezing weather. The Japanese trifoli ate orange is hardy, but has fruit of small size. It is hoped that a hybrid may be obtained be tween it and the ordinary orange which shall have increased hardiness without loss of size or flavor in the fruit. (c) Adaptation to Warmer Climate. The Kieffer and L•Conte pears. which have revolutionized pear agriculture by extend ing the range of pnditable pear-growing hundreds of miles southward, are said to be hybrids be tween the common pear and the Chinese sand pear. (d) Increased Resistance to Disease. When the vast grape industry of France was threatened with destruction on account of the ravages of the Phylloxera. immune American species were erossed with the French species and im munity was gained by them. Similarly, the blaek-rot disease in grapes has been fought by introdneine. the blood of immune races. (e) ln ereased Percentage of Starch. Sugar, etc. By- hy bridization the production per acre of the potato has been doubled. and the starch percentage in ereased from 15 to 20. While the percentage of
sugar in the sugar-beet has been hitherto chiefly increased by selection, there seems to he a ehanee for improvement by hybridization. A hybrid cinchona produce: three to four times the ordi Lary percentage of quinine. (f) Change of Sea son and Duration of Life. By hybridization plants have arisen fruiting at unusual times. like Bur bank's blackberry and raspberry hybrids. A fair ly successful attempt to make the pansy peren nial resulted from crossing the garden pansy with the perennial Viola cornuta. (g) Acquisi tion of Odor. The fragrance of the pansy has been improved by crossing with odoriferous Al pine species. (h) Improvement of Quality and Flavor. This result is illustrated by the case of smoking tobaccos, in which the superior-flavored Havana race has been crossed with other races having larger leaves, so that a greater quality of well-flavored leaf has been produced. Alto gether, many breeders conclude that by syste matic hybridization most species of plants will be found capable of almost indefinite improve ment.
In connection with the artificial production of hybrids, the phenomenon of has re cently attracted much attention. This term is applied to cases in which characters of the pol linating parent appear directly in the fruit or seed. It was once thought that only the embryo could show hybrid characters, which would become evident. therefore, only upon the germination of the seed. In eases of xenia, how ever, the regions of the seed outside of the em bryo show hybrid characters, so that it is evident that they too have been influenced by the pol linating parent. The crossing of the races of maize has proved to be most favorable for study ing this phenomenon. If a race of maize nor mally producing white grains be pollinated by one producing red grains. the resulting grains will show the red coloration in various ways. The same result is also obtained in crossing races of sweet and dent corn. This phenomenon was inexplicable until the recent discovery of 'double fertilization' among flowering plants. This phrase means that both of the male cells were brought by the pollen-tube to the ovule function—one fertilizing the egg, which then produces the embryo, the other uniting with the 'endosperm nucleus.' which then produces the endosperm or food substance of the seed about the embryo. It is evident, therefore, that where double fertiliza tion occurs in connection with hybridizing, the endosperm as well as the embryo is a hybrid, and that the resulting seed may show characters of the pollinating parent. See ANGIOSPERMS; FER