CH. v] MUTATION 49 



the jungle, the chances are that it will inherit the suitability of 

 its parents to the local conditions, and that if the mutation be not 

 seriously harmful, it will not be interfered with in any way by 

 natural selection, and will be allowed to survive, and in time, if 

 hereditary, to propagate itself. May it not be that something of 

 this kind is an explanation of the great majority of the innu- 

 merable structural differences that we see in plants, and which 

 so often only appear when the serious struggle for existence is 

 over, or practically over? One cannot imagine that it can have 

 any importance in the struggle for existence whether a plant 

 have or have not one or two cotyledons, a parallel- veined or a 

 net-veined leaf, a 3-merous or a 5-merous flower, and so on. To 

 the vast majority of the characters upon which we base our 

 classifications natural selection is probably completely indif- 

 ferent. It is well known, incidentally, that most of those 

 characters which we consider as usually of family rank (App. I) 

 may at times appear as generic, or even specific, so that it is 

 evidently quite easy for them to be acquired, while at the same 

 time the structural agreement between them is amazing. Nothing 

 but sudden mutation will easily account for such phenomena. 



A case in which mutation of this kind looks as it might have 

 happened in nature is that of the columbine {Aquilegia), which 

 looks as if it might have arisen from the larkspur {Delphinium), 

 the latter having a dorsiventral flower with one spur, the former 

 a regular flower with five spurs. Nothing but mutation can cross 

 the (numerical) gap between these genera, and one actually sees 

 an almost exactly similar mutation happening frequently in the 

 toad-flax. 



A good illustration (and dozens similar to this could be given) 

 of the very great probability of large mutation is that afforded 

 by the three families Centrolepidaceae, Eriocaulaceae, and 

 Restionaceae, all of which, independently, split into two sections, 

 Diplantherae with dithecous anthers, and Haplantherae with 

 monothecous. One cannot conceive of this by anything but a 

 direct mutation, which would produce morphological similarity 

 in all. 



Some quotations bearing upon this subject may be made from 

 a paper now of some age (57), in which attempts were made to 

 show that local or endemic species were usually separated from 

 the widely distributed, and usually fairly closely related, species 

 that accompanied them by differences which could only be 

 passed over by mutations, often "large". 



WED A 



