154 INBREEDING AND OUTBREEDING 



Advances in average weight of seed ranging from 3 to 21 

 per cent, were obtained. With inbred strains as parents, 

 the increases are even greater, ranging from 5 to 35 per 

 cent. The seeds have a heavier embryo as well as a 

 heavier endosperm, yet curiously enough they mature 

 faster than the selfed seeds on the same ears. 



It is a point of some interest, perhaps, that there is no 

 selective action favoring the foreign pollen when these 

 pollen mixtures are applied. This matter has been deter- 

 mined very carefully on account of its bearing on Men- 

 delian theory, but it also answers in the negative the 

 question of whether there is an effect of heterosis 

 manifested by a selective chemotropism before the zygote 

 is formed. 



Darwin, in ' ' Cross and Self -Fertilization in the Vege- 

 table Kingdom," compares the time of flowering of 28 

 crosses between different types of plants which had shown 

 distinct evidence of hybrid vigor. Of them, 81 per cent, 

 flowered before the parents. In other cases, where no 

 heterosis was shown in other characters there was no ac- 

 celeration of the blooming period. These results have 

 been corroborated in crosses between garden varieties of 

 tomatoes and of sweet corn, where a tendency to put for- 

 ward the time of both flowering and maturing has been 

 shown to accompany increases in size. Shortening the 

 time of growth thus seems to be one of the many ex- 

 pressions of an increased metabolic efficiency on the part 

 of the hybrid plant. 



Increased longevity, viability, endurance against un- 

 favorable climatic conditions, and resistance to disease 

 have also been frequently noted as properties of hybrids. 

 Kolreuter 125 and Wiegmann 70 both mention these points, 



