Hybridization 109 



nized as distinct. It was formerly supposed that all 

 hybrids were more or less sterile, in contradistinction to 

 crosses, which were thought to be very fertile. It has 

 been found, however, that many hybrids, in the narrow 

 sense, are very fertile, and that some crosses are nearly 

 sterile. Since it is impossible to indicate by any two words, 

 such as hybrid or cross, the various degrees of difference 

 of the forms crossed, the word hybrid is now generally 

 used as a generic term to include all organisms arising 

 from a cross of two forms noticeably different, whether the 

 difference be great or slight. Adjectives are sometimes 

 used to indicate the grade of the forms crossed, such as 

 racial hybrids, bigeneric hybrids, and so forth. 



The offspring produced by the union of two plants 

 identical in kind, but separated in descent by at least 

 several seed generations, is often called a cross, cross- 

 fertilized, or cross-bred plant, but it is not a hybrid, as 

 the essential character of a hybrid is that it results from 

 the union of plants differing more or less in kind, or, in 

 other words, is the result of a union between different races, 

 varieties, species, or genera. On the other hand, flowers 

 impregnated with their own pollen, with the pollen of 

 another flower on the same plant, or even pollen from 

 another plant derived from the same original stock by 

 cuttings or grafts, are said to be self-fertilized, and the 

 offspring resulting from such unions are often termed self- 

 fertilized plants. Strictly speaking, however, self- or close- 

 fertilization is impregnation with pollen of the same flower. 

 With such plants as tobacco and wheat, self-fertilization 

 is the rule. In many cases, however, the flowers are so 

 constructed that cross-fertilization is favored, as in corn 



