PLANT LIFE. 55 



grees below freezing, while the trifoliate orange en- 

 dures a temperature down to zero or colder. The 

 fruit of the latter is, however, practically inedible. 

 The U. S. Dept. of Agriculture succeeded in crossing 

 the trifoliate and the sweet orange, obtaining a num- 

 ber of seeds. Of the plants obtained from these seeds 

 many were worthless but some bore edible fruits, not 

 so good as the sweet orange it is true, but far superior 

 to the fruit of the trifoliate orange. Furthermore, 

 they are capable of enduring considerable cold, thus 

 enabling farmers to grow a kind of orange far north 

 of the orange belt. The watermelon is subject to a 

 disease which spreads through the soil and entering 

 the roots causes the plant to die by choking up the 

 water-conveying vessels, whence the name " wilt " is 

 applied to the disease. The inedible stock melon or 

 citron is not subject to the disease. By crossing the 

 latter on a choice variety of watermelon, and selecting 

 and inbreeding for several generations those of the 

 progeny that possessed the right color, shape, vigor, 

 abundance of melon and resistance to the disease have 

 been produced. By crossing the slow-growing black 

 walnut with the Japanese walnut, Luther Burbank of 

 California has produced a variety of walnut very 

 rapid in its growth, and yet possessing wood of an ex- 

 cellent quality. 



Methods of Hybridization. The methods used are 

 essentially as follows: For the two parents are chosen 

 closely related species, or plants of different varieties 

 of the same species, each possessing certain charac- 

 teristics which it is desired to combine in the new va- 

 riety sought. One is chosen to bear the seed and one 

 to furnish the pollen. Some flowers of the former 

 are selected shortly before they are ready to open, 

 and the petals are removed with scissors or pried apart 

 and the yet unopened stamens removed, disturbing the 

 flower as little as possible. This is to prevent any 

 chance of self-pollination. These flowers are then 

 enclosed in paper bags so as to prevent the access of 



