123 



common to the related parents, and only indirectly on their 

 relationship in so far as they are apt to resemble each other 

 in all respects, including their sexual nature." Secondly, it 

 will depend on a sexual element of the parents. The pro- 

 genitors having been in some way exposed to diflerent 

 conditions, having been intercrossed. Thirdly, what Darwin 

 calls spontaneous variation. Everyone is familiar with the 

 practice of g.irdeners to obtain seed from different localities. 

 The product is undoubtedly better, since the seeds were 

 grown in soils of very different nature as well as climatic 

 conditions. It would no doubt be better, as Darwin' sug- 

 gests, to sow the seeds raised in different localities in 

 alternate rows. By crossing there would be a blending of 

 "the whole organization without in any way affecting the 

 purity of the variety. Darwin made many experiments to 

 determine the superiority of cross-fertilized plants over self- 

 fertilized plants. I will give a few illustrations: A plant of 

 cultivated morning glory {TpomcBa purpurea), grown from 

 carefully selected seed, when ready to flower was protected 

 with meshes one-tenth of an inch in diameter so that insects 

 carrying pollen might be excluded. Ten flowers were fer- 

 tilized with pollen from the same flower (self-fertilized). 

 Ten other flowers on the same plant were crossed (cross- 

 fertilized) with pollen from a distinct plant. The cross and 

 self-fertilized plants were placed in damp sand and allowed 

 to germinate. The two kinds were then placed under the 

 same conditions. This was done during ten generations. 

 At the end of the experiment the product of the cross was 

 superior to the self-fertilized in every respect. In produc- 

 tiveness of capsules, the ratio of crossed to self-fertilized in 

 the third generation was at 100-38. It is also noteworthy 



7 Cross-fertilization, etc. p. 28, p, 58, etc. 



