No. 4.] CROSSING OF PLANTS. 39 



outset that the characters of hybrids, as compared with the 

 characters of simple crosses between stocks of the same vari- 

 ety, are ambiguous, negative, and often prejudicial. The 

 fullest discussion of hybrids has been made by Focke, and 

 he 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, although per- 

 haps true in the main, appears to be too broadly and posi- 

 tively stated. 



2. "The characters of hybrids are 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, cross- 

 breeds are, as a rule, uncommonly vigorous ; they are dis- 

 tinguished mostly by size, rapidity of growth, early flower- 

 ing, productiveness, longer life, stronger reproductive power, 

 unusual size of some special organs, and similar character- 

 istics." 



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 apt to appear in 

 hybrids, especially in the flowers." 



Some of the relations between hybridization and crossing 

 with narrow limits are stated as follows by Darwin : " It is 

 an extraordinary fact that with many species flowers fertilized 

 with their own pollen are either absolutely or in some degree 

 sterile ; if fertilized with pollen from another flower on the 

 same plant, they are sometimes, though rarely, a little more 

 fertile ; if fertilized with pollen from another individual or 

 variety of the same species, they are fully fertile ; but if 



