CHxi] B. MORPHOLOGICAL 131 



leaf come to develop stomata, intercellular spaces, palisade and 

 spongy tissue, and the fine network of veins, and how did it 

 develop these last in so many patterns of netting, parallelism, etc.? 



Correlation, if large, implies that most characters have no 

 bearing upon natural selection, and do not interfere with the 

 results gained by the first character. And as differences in one 

 character only do not usually cause mutual sterility, one wonders 

 how that comes to be so common a mark of specific difference. 



One must look with great suspicion upon such easy interpreta- 

 tions of things as calling them direct adaptations. If they were 

 formed as such, the work was too complicated for natural selec- 

 tion. It is more probable that they were formed at one step, and 

 not being harmful, were allowed by natural selection to survive. 



9-2 



