1 62 APPENDIX I DIVERGENT EVOLUTION. 



If there is any persistent cause by which local and social groups are 

 broken up and promiscuously intermingled before recognizable char- 

 acters are gained, the entrance of sexual segregation will be prevented. 

 I therefore conclude that the chief influence of this latter factor is 

 found in its prolonging and fortifying the separate breeding of varie- 

 ties that have arisen under local, social, or industrial segregation, and 

 in thus continuing the necessary condition for the development of 

 increasingly divergent forms of intensive segregation, under which the 

 organism passes by the laws of its own vital activity when dealing 

 with a complex environment in groups that never cross. 



12. Germinal Segregation is Caused by the Propagation of the Species by means of 



Seeds or Germs, any one of which, when developed, forms a community so 

 related that the members breed with each other more frequently than with the 

 members of other communities. 



If the constitution of any species is such that the ovules produced 

 from one seed are more likely to be reached and fertilized by pollen 

 produced from the same seed than by pollen produced from any other 

 one seed, then germinal segregation is the result. 



In order to secure this kind of segregation it is not necessary that 

 the flowers fertilized by pollen from the same plant should be more 

 fertile or the seeds capable of producing more vigorous plants than 

 the flowers fertilized by pollen from another plant. All that is re- 

 quired is that the seeds produced by each individual plant shall be 

 fertilized by the pollen of the same plant. 



This form of segregation is closely related to local segregation on 

 one side and to social segregation on the other. It, however, differs 

 from the former in that it does not depend on migration or trans- 

 portation, and from the latter in that it does not depend on social 

 instincts. 



13. Floral Segregation is Segregation arising from the Closest Form of Self-fertiliza- 



tion, namely, of the Ovules of a Flower by Pollen from the same Flower. 



Some plants that in their native haunts are frequently crossed by 

 the visits of insects depend entirely on self-fertilization when trans- 

 ported to other countries where no insect is found to perform the same 

 service for them. The common pea (Pisum sativum) is an example 

 of a species that does not fail of propagating in England, though Dar- 

 win found that it was very rarely visited by insects that were capable 

 of carrying the pollen, and the pollen is not carried by the wind.* 

 Darwin also mentions Ophrys apifera as an orchid which ' ' has almost 

 certainly been propagated in a state of nature for thousands of gen- 

 erations without having been once intercrossed, "f 



* Cross and Self Fertilization in the Vegetable Kingdom, p. 161. t Ibid., p. 439 



