CH. XII] C. TAXONOMIC 135 



asmuch as they will have inherited their characters from the 

 point that is the farthest back that is possible — the earliest 

 mutational divisions that took place in the family concerned. 



In deciding this point we must, of course, work with the keys 

 with which the taxonomists have provided us, but the latter 

 have, of course, taken the greatest possible pains to find the most 

 widely different characters that mark the different groups. In 

 their keys they usually begin with very divergent characters, 

 inasmuch as they have learnt by experience that these mark the 

 largest divisions in the great majority of cases, separating the 

 genera first of all into tw^o large groups. These groups again are 

 separated by the most different characters that can be found, but 

 which do not mark the whole, but only a part of the first group. 

 And so on, breaking up the family into allied groups within 

 allied groups — the general principle of all classification. 



One will, therefore, expect that the first one, two, or at most 

 perhaps three separations that are given in any ordinary good 

 key will separate not only the chief sub-families or tribes, but 

 also the largest genera, and one will expect these to be separated 

 by such distinct and divergent characters that there will be little 

 or no difficulty in picking them out from one another. When such 

 difficulty occurs, it should be in genera that have become so large 

 that their outlying species, which will have been liable to more 

 change than the earlier and more "genus-like" ones, have in one 

 or two cases reached almost to the overlapping point. We should 

 expect, but have not had sufficient time to test the matter, that 

 these difficult species would prove in general to be comparatively 

 local, that is to say, on the whole, the youngest species in their 

 genera, which will have gone through the greatest number of 

 mutations since the first throwing of the genus. 



As a test of this case, we may take the family Ranunculaceae, 

 which is already described from this point of view in the chapter 

 upon Differentiation. The first division of the family in most keys 

 throws the largest genera on both sides. Here, for example, 

 Aconitu77i, Aquilegia and Delphinium have follicles, and Anemone, 

 Clematis, Ranunculus and Thalictrum have achenes. But as the 

 two actually largest genera are Clematis and Ranunculus, 

 separated by the very divergent character of opposite or alter- 

 nate leaves, it is possible that this was the very first mutation, 

 and that Clematis mutated off no other genera with opposite 

 leaves. Or yet again, we must always bear in mind the possi- 

 bilities of such complex mutations as are indicated in Hayata's 



