CH. v] MUTATION 47 



When one looks at the great differences that exist, for example, 

 between the Dicotyledons and the Monocotyledons, and these in 

 several different points, it seems to be an unnecessary handicap 

 to accept the idea that mutations must necessarily be small, 

 especially when we have no facts to prove that this must be the 

 case. The characters are so completely unrelated to anything in 

 the way of adaptation that it becomes very difficult to conceive 

 of them as having been gradually acquired, especially when one 

 remembers that intermediates between them are all but im- 

 possible, and could not in any case have any adaptational value, 

 so that unless there is some recondite law in the background 

 that can force things to proceed in such a manner, there seems no 

 reason for it. There might for example, be (probably is) some 

 physical or chemical law that at present we do not know, com- 

 pelling genes or chromosomes to behave in a certain way.^ But 

 as one sees the phenomena at present, how can one pass by 

 gradual stages from two cotyledons to one (or vice versa), from 

 net veining to parallel, from a 5-merous to a 3-merous flower, 

 from the one kind of anatomy to the other? The only reasonable 

 way to account for it is to suppose that the characters of Mono- 

 and Dicotyledons were handed down as the lines of descent 

 resulting from a mutation in very early times which split off the 

 one from the other. No adaptational difference can be found, nor 

 is there any " monocotyledonous " mode of life. As one comes up 

 the scale from species, the plants are found to grow in greater and 

 greater variety of conditions, and to belong to more and more of 

 the various ecological groups. If monocotism suit a grass or a 

 bamboo better than dicotism, why does it also suit a tulip, a 

 Zostera, a Potamogeton, an iris, or an orchid? And why, if there is 

 any adaptational difference betw^een the two great groups, do 

 they occur with such regularity in almost every part of the world 

 in the proportion of one to four? There are small places where 

 these figures vary very much, but the only large ones are usually 

 near the limits of vegetation, a fact which suggests that there are 

 differences in age between the two groups. Hooker pointed out 

 this numerical relationship in 1888 (18), and it remains one of the 

 many problems in geographical distribution which are com- 

 pletely inexplicable upon the hypothesis of natural selection, and 

 which are left unmentioned by its supporters. 



Another direction in which the theory of mutation makes 



^ My friend Dr C. Balfour Stewart suggests that it is probably electrical, 

 as is probably the spUtting of the chromosomes in reproduction. 



