82 DIVERGENCE OF VARIATION [ch. ix 



The intermediate genera are : 



Total 133 or 10 per cent of the family 



The small genera are: 



Total 43 or 3 per cent of the family 

 Grand total 1356 spp. in 26 genera, average 



52. 



The classification used here is that of Engler and Prantl, in 

 their first edition — Paeonieae (A 1) and Helleboreae (A 2) being 

 marked off" from Anemoneae (B); Paeonieae have only two 

 genera. Of the large genera given above, three belonging to 

 group A 2 have an average of 133 species per genus, and are only 

 North temperate in distribution, while four belong to group B, 

 average 195, and are cosmopolitan in distribution in three cases, 

 the fourth being only North hemisphere. On the face of it, by the 

 greater size and greater distribution, B would appear to be an 

 older group than A. The intermediate genera are intermediate 

 both in size and in distribution, and the small genera are evidently 

 the lowest in both respects. 



Now the very old and large genera, upon the theory of dif- 

 ferentiation, must owe their origin to the earliest generic muta- 

 tions in the family, and upon the principle of divergence of 

 variation, we shall expect these variations to be, on the whole, the 

 most divergent that occur in the family. In other words, the 

 larger genera of a family should be separated by well-marked 

 divergences, while the smaller will be less so. This is exactly what 



