LUTHER BURBANK 



precisely because of their independence. The 

 method of cross-fertilization that they have 

 adopted does indeed enable some of them to 

 blend the strains of different individual plants; 

 but in every instance the parents must be growing 

 in the immediate vicinity of each other. 



Except by the accidental and most unusual 

 transfer of a plant through the agency of a 

 passing animal, there is hardly the remotest 

 chance of effecting cross-fertilization between 

 individual mosses or lichens or ferns growing in 

 widely separated regions. 



But we have already seen that it is precisely 

 this blending of traits brought from parents 

 growing under different environing conditions 

 that is chiefly responsible for making plants vary 

 and furnishing the materials for evolutionary 

 progress. So it goes without saying that the plants 

 that are restricted, in the choice of possible mates, 

 to individuals growing under the same conditions 

 to which they themselves are subjected, cannot 

 expect to change rapidly and therefore do not 

 evolve in any such ratio as plants having the 

 other habit. 



And in point of fact we find that the plants that 

 retain this primitive custom of fertilization with 

 the aid of motile germ cells, acting quite inde- 

 pendently of insect or wind, are plants of a 



[64] 



