Hybrid Vliior 165 



\iuj()r amounts to an increase in the si/r of tells, as well 

 as multiplication in the number of cells; in oilier words, 

 an increase in the ]X)wer of assimilation. \'ial)ilit\' of 

 seeds is increased, and the more rapid growth and earlier 

 maturity of the seedlings is quite noticeable. 'I'ime 

 of flowering and maturing is hastened, although in many 

 cases increased longevity has been brought about. 

 One sees a distinct increase in the size of the roots. 

 In the stem there is no increase in the number of nodes, 

 but the internodal development is striking. (The gain 

 in size in plants which are more or less determinate 

 in their number of parts is made up of an increase 

 in the size of parts rather than in the number of parts.) 

 Usually the stem growth is greater than the leaf growth, 

 but the increase of the latter can be definitely traced. 

 The size of the flower is usually not affected, nor is there 

 any change in the size of small fruits, such as tobacco. 

 In fleshy fruits, however, such as tomato and egg plant, 

 there is a marked increase. On the individual plant 

 there are distinctly more flowers and fruits, and in some 

 cases separate inflorescences are longer, as in the ears of 

 corn. (Total yield in corn has, in some crosses, been 

 increased 100 per cent or more.) Endurance against 

 unfavorable environmental factors and resistance to 

 disease have also been frequently noted as properties of 

 hybrids. Facility of vegetative pro])agation is increased. 

 (Moreover, there is no evidence to i)ro\e that plants lose 

 any of their hybrid \ igor in long continued vegetative 

 multiplication through innumerable generations.) 



In general, there is similarity between hybrid \ igor 

 and the effect of a good environment. Those characters 

 which arc the quickest to be mcKliiied by external factors 



