40 PLANT BREEDING. 



plants which, when multiplied into varieties, will average better than 

 the parent varieties. No matter should all but one in a thousand be 

 discarded, if that one will produce a race of progeny with the improved 

 qualities. With this theorj- of hybridizing and the practice of mak- 

 ing a very large number of crosses, giving each a few years or genera- 

 tions in which to show the tendencies of its progeny when grown in 

 large numbers, and with a systematic plan of eliminating, the use of 

 hybridizing in variety formation becomes a practical and very power- 

 ful agency in plant improvement. 



HYBRIDS AND CROSSES DEFINED. 



Very much has been written concerning hj'brids, and this literature 

 contains the results of many experiments. Swingle and Webber have 

 summarized the facts well.^ They use the word "hybrid" to mean a 

 plant resulting from cross fertilizing plants differing in their relation- 

 ships, whether that difference is great, as in species or even in genera, 

 or comparatively slight, as in distinct varieties. Cross-bred i^lants 

 are those which have resulted from the cross fertilization of plants 

 within the variety but separated in descent by at least some genera- 

 tions of seed production. Self-fertilized plants, on the .other hand, 

 are those which have resulted from the pollen of the same plant 

 impregnating the flower, including those plants which have arisen 

 from buds and cuttings from th« same seminally produced plant. 



IMPORTANCE AND METHODS OF HYBRIDIZING. 



The operation of cross pollinating in hybridizing is easy in the case 

 of most useful plants. This work forms but a small part of the work 

 of variety formation, most of the labor and expense being connected 

 with collecting and testing to find superior foundation stocks, with 

 the growing and selecting of large numbers of hj-brid plants and with 

 testing the resulting varieties that only the best may be propagated 

 and disseminated. The methods of hybridizing wheat, corn, and 

 apples, and a few other plants will be given briefly on future pages, 

 as illustrative of the work with some classes of plants. It is neces- 

 sary fully to understand the structure and habits of the flowers of the 

 plant to be dealt with, but no great skill or profound knowledge need 

 be attained, and the necessary appliances are few and simple. In 

 case of crosses between nearly related plants there is often little more 

 variation than among self-fertilized plants. Where varieties not too 

 distant in relationship are hybridized the variation, according to 

 Swingle and Webber, usually shows in the first as well as in the suc- 

 ceeding generations, but where the relationship of the parents is verj- 

 wide, as between species or genera, the hybrids are more likely to be 

 intermediate in appearance between the two types for the first genera- 



' Hybrids and their Utilization in Plant Breeding. Yearbook, U. S. Dept. Agr., 

 1897, pp. 383-420. 



