l^HROTTQH CUMULATIVE SEGREGATIOH". 



237 



influence of tliis latter factor is found in its prolonging and 

 fortifying the separate breeding of varieties that have arisen 

 under Local, Social, or Industrial Segregation, and in thus con- 

 tinuing the necessary condition for the development of increas- 

 ingly 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 Grerminal Segregation is 

 the result. 



In order to secure this kind of Segregation it is not necessary 

 that the flowers fertihzed 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 required is that of the seeds produced a larger number 

 shall be fertilized by the pollen of the same plant than by the 

 pollen of any other one plant. 



This form of Segregation is closely related to Local Segre- 

 gation on one side, and to Social Segregation on the other. It, 

 however, diflers from the former in that it does not depend on 

 Migration or Transportation, 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-fertilization, namely the fertilization of the ovules of 

 a flower by pollen from the same flower. 



Many plants that in their native haunts are frequently crossed 

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

 transported to other countries where no insect is found to per- 

 form the same service for them. The common pea (Fisum 

 sativum) is an example of a species that habitually fertilizes 

 itself in England, though Darwin found that it was very rarely 

 visited by insects that were capable of carrying the pollen.* 

 Darwin also mentions Ophrys apifera as an orchid which " has 



* See ' Cross- and Self-Fertilization in the Vegetable Kingdom,' p. 161. 

 LINN. JOUKN. — ZOOLOGY, VOL. XX. 19 



