CROSSING AND VIGOR OP OFFSPRING 



583 



the loss of vigor in the offspring. Hybrids are usually more 

 vigorous than their parents. Corn grown from seed resulting 

 from self-fertihzation shows much loss in vigor and consequently 

 does not yield so well {Figs. 4.86 and J^7). The difference in 

 yield between plants resulting from crossing and plants resulting 

 . from self-fertiUzation often amounts to several bushels per acre. 



r 



FtG. 490. — Increase in size of fruits in Cucumbers as a result of crossing. 

 a and c show size of fruits borne by the parents and 6, the size of fruits borne 

 by the first generation of the cross. After Halsted. 



Darwin found that Cabbage plants obtained by crossing were 

 nearly three times the weight of those obtained by self-fertihza- 

 tion. In Buckwheat Darwin obtained plants much taller and 

 about one-fifth better in yield by crossing. In Lettuce, Beets, 

 Pumpkins, Squashes, Tomatoes, and many other plants {Fig. 

 488), it has been shown that crossing produces more vigorous 

 offspring. 



