302 EXPERIMENTS WITH PLANTS 



exceeded those from self-pollination as 100 to 76. He 

 carried this out to the tenth generation, when the pro- 

 portion was 100 to 54. The average was about 100 to 

 77, or about 30 per cent gain. There was also a cor- 

 responding gain in fertility. In this case the cross- 

 pollination was with plants growing near together; on 

 bringing pollen from plants growing in another gar- 

 den, it was found that the plants obtained exceeded 

 the cross -pollinated plants previously obtained as 100 

 to 78 in height, as 100 to 57 in number of seed-pods, 

 and as 100 to 51 in the weight of seed-pods: that is, 

 they were nearly 30 per cent more vigorous and, as 

 compared with self -pollinated, over 44 per cent more 

 vigorous. Similar results were obtained with Cabbage, 

 Buckwheat, Beets, Corn and Canary Grass. 



It appears, therefore, that cross -pollination is more 

 advantageous to the plant than self-pollination, and 

 there are numerous devices in flowers which promote 

 cross -pollination and prevent self-pollination. An 

 effective means of preventing self-pollination is to 

 have the anthers and ovaries borne in separate flowers ; 

 both kinds of flowers being on the same plant, as 

 in the Squash, Walnut, Pine, Corn, Castor- bean, etc. 

 (termed monoecious), or the staminate (pollen-bearing) 

 flowers on one plant and the pistillate (ovary -bearing) 

 on another, as in the Hop, Poplar, Willow, etc. 

 (termed dioecious) . Study as many cases of this kind 

 as you can. 



