CH. XI] B. MORPHOLOGICAL 109 



has to do with the life of the plant, the more important is it from 

 a taxonomic point of view. The higher one goes from species to 

 family, the less connection have the characters with the life, and 

 if one tries to think out how a mechanism like natural selection, 

 depending upon improved adaptation, could thus have less and 

 less to do with adaptation, the more it separated into larger 

 groups the organisms with which it was concerned, one will 

 speedily arrive at a deadlock. 



Two species usually differ in more than one character, even 

 when closely related, and among the supporters of natural selec- 

 tion it is, or has been, very often an implied assumption that a 

 species A shall change fully to B before it goes on to become C. 

 But one can see no reason whv this should be so : a variation in 

 the direction of C would probably be just as useful in a plant that 

 was only on the way to B. Natural selection can do nothing till 

 the right variation is offered to it. Let us suppose that A is 

 offered a variation in the direction of B and has started to adopt 

 it, and that then a new variation is offered in the direction of C, 

 obviously better, but in a different direction. What will happen 

 then? Will it go on towards B and ignore the later offer, will it 

 form C with a shade of B about it, or will it try to go back, and 

 get rid of the traces of B, with the risk that it may not get another 

 offer of C? There seems almost nothing for it but to demand that 

 variations shall not interfere with one another, but that the one 

 "in possession" shall be allowed to finish what it began, before 

 another one is allowed to start. But this will greatly slow down 

 the process of evolution, unless the variations are largely corre- 

 lated. But why under natural selection should there be so much 

 correlation? It is hard enough to find adaptational reasons for 

 one variation, let alone half a dozen correlated ones. It would 

 seem more probable and reasonable that in general the morpho- 

 logical characters have no necessary physiological value, and are 

 therefore not the result of any adaptational selection. If a new 

 structural character appears that has an adaptational value, it is 

 at once seized upon and perpetuated, unless in case of evil 

 chance. But to regard structural characters as necessarily 

 showing individual adaptational value — for example, that there 

 is some necessary value in a pinnate rather than a palmate leaf, 

 or vice versa — is to stretch the theory of gradual adaptation 

 too far. 



It is a very remarkable thing that we do not find plants with 

 a superposition of variations, one complete, the other incomplete. 



