238 



llEV. J. T. GULTCK O^f DIVERGENT EYOLTJTIOlf 



almost certainly been propagated in a state of nature for thousands 

 of generations without having been once intercrossed." * 



General Observations on Germinal and Floral Segregation. 



A fact of great importance in its bearing on the origin of 

 varieties should be here noted. Any variation, arising as a so- 

 called sport, in any group of plants where either of these prin- 

 caples is acting strongly will be restrained from crossing, and will 

 be preserved except in so far as reversion takes place. Now 

 there is always a possibility that some of the segregating branches 

 of descent will not revert, and that, through the special character 

 which they possess in common, they will some time secure the 

 services of some insect that will give them the benefit of cross- 

 fertilization with each other without crossing with other varieties. 

 The power of attaining new adaptations may be favoured by self- 

 fertilization occasionally interrupted by interbreeding with indi- 

 viduals of another stock ; for the latter is favourable as intro- 

 ducing vigour and variation, and the former as giving opportunity 

 for the accumulation of variations. 



(h) Impeegnational Segeegation. 



Impregnational Segregation is due to the different relations in 

 which the members of a species stand to each other in regard to 

 the possibility of their producing fertile olfspring when they 

 consort together. 



In order that Impregnational Segregation should be established 

 and perpetuated it is necessary, 1st, that variation should arise 

 from which it results that those of one kind are capable of pro- 

 ducing vigorous ai^d fertile offspring in greater numbers when 

 breeding with each other than when breeding with other kinds ; 

 2nd, that mutually compatible forms should be so brought to- 

 gether as to ensurt! propagation through a series of generations. 

 In order to secu. /e this second condition, it is necessary that, in 

 the case of plants there should be some degree of Local, Germinal, 

 or Floral Segregation, and, in the case of animals that pair, 

 either pronounced Local Segregation, or partial Local Segre- 

 gation supplemented by Social or Sexual Segregation. The first 

 of these factors I call Negative Segregation, as contrasted with all 



* .See 'Cross- and ,^elf- Fertilization in the Vegetable Kingdom,' p. 439. 



