30 Mutual Independence of Hereditary Characters 



and simpler than in the animal kingdom, in which es- 

 pecially the exclusive limitation of propagation of the 

 higher animals to the sexual method makes us only too 

 easily over-estimate the significance of this process. To 

 this must be added the fact that, for the vegetable king- 

 dom, quite an unexpected light has been thrown on the 

 nature of this process through the exhaustive compara- 

 tive study of the significance of cross- and self-fertiliza- 

 tion, for which we are indebted to Darwin. 



Darwin's experiments have taught us that the essence 

 of fertilization consists in the mixing of the hereditary 

 characters of two different individuals.^*^ Self-fertiliza- 

 tion, which takes place so readily in the vegetable king- 

 dom, and is so easily accomplished experimentally, has 

 not by any means the same significance. From seeds 

 obtained in the last named manner the individuals pro- 

 duced were always weaker in Darwin's experiments than 

 those obtained in a crop from crossed flowers. The 

 first ones were smaller, with less profuse branching, flow- 

 ering less abundantly and less constantly, and accordingly 

 they bore less seed. Crossing two flowers of the same 

 plant was more deterimental than the pollination of the 

 flowers with their own pollen. 



Even the crossing of different individuals was not suf- 

 ficient to keep the species normal when it was cultivated 

 year after year in the same bed, and protected from being 

 fertilized by specimens of a different origin. The whole 

 colony deteriorated steadily and distinctly in the course 

 of a few years ; not only did the plants become smaller and 

 weaker, but their individual differences decreased so much 

 that they resembled each other almost completely. A 



i^Darwin, Origin of Species. 6 Ed., pp. 76-79, and Cross and 

 Self Fertilization in the Vegetable Kingdom. 1876. 



