124 Plant- Breeding 



often prejudicial. Focke lays down the five following 

 propositions concerning the character of hybrid offspring : 



1. "All individuals which have come from the crossing 

 of two pure species or races, when produced and grown 

 under like conditions, are usually exactly like each other, 

 or at least scarcely more different from each other than 

 plants of the same species are." This proposition, al- 

 though perhaps true in the main, appears to be too broadly 

 and positively stated. 



2. "The characters of hybrids may be different from 

 the characters of the parents. The hybrids differ most in 

 size and vigor and in their sexual powers. 



3. "Hybrids are distinguished from their parents by 

 their powers of vegetation or growth. Hybrids between 

 very different species are often weak, especially when 

 young, so that it is difficult to raise them. On the other 

 hand, crossbreds are, as a rule, . uncommonly vigorous ; 

 they are distinguished mostly in size, rapidity of growth, 

 early flowering, productiveness, longer life, stronger repro- 

 ductive power, unusual size of some special organs, and 

 similar characteristics. 



4. "Hybrids produce a less amount of pollen and fewer 

 seeds than their parents, and they often produce none. 

 In cross-breeds this weakening of the reproductive powers 

 does not occur. The flowers of sterile or nearly sterile 

 hybrids usually remain fresh a long time. 



5. "Malformations and odd forms are likely to appear 

 in hybrids, especially in the flowers." 



Some of the relations between hybridization and cross- 

 ing within narrow limits are stated as follows by Darwin : 

 " It is an extraordinary fact that with many species flowers 



