Chap. II. SPECIES OF LARGE GENERA VARIABLE. 55 



generally much more widely diffused than plants higher 

 in the scale ; and here again there is no close relation 

 to the size of the genera. The cause of lowly-organised 

 plants ranging widely will be discussed in our chapter 

 on geographical distribution. 



From looking at species as only strongly-marked and 

 well-defined varieties, I was led to anticipate that the 

 species of the larger genera in each country would oftener 

 present varieties, than the species of the smaller genera ; 

 for wherever many closely related species (i. e. species of 

 the same genus) have been formed, many varieties or 

 incipient species ought, as a general rule, to be now 

 forming. Where many large trees grow, we expect to 

 find saplings. Where many species of a genus have 

 been formed through variation, circumstances have been 

 favourable for variation ; and hence we might expect 

 that the circumstances would generally be still favour- 

 able to variation. On the other hand, if we look at 

 each species as a special act of creation, there is no 

 apparent reason why more varieties should occur in a 

 group having many species, than in one having few. 



To test the truth of this anticipation I have arranged 

 the plants of twelve countries, and the coleopterous 

 insects of two districts, into two nearly equal masses, the 

 species of the larger genera on one side, and those of the 

 smaller genera on the other side, and it has invariably 

 proved to be the case that a larger proportion of the 

 species on the side of the larger genera present varieties, 

 than on the side of the smaller genera. Moreover, the 

 species of the large genera which present any varieties, 

 invariably present a larger average number of varieties 

 than do the species of the small genera. Both these 

 results follow when another division is made, and when 

 all the smallest genera, with from only one to four spe- 

 cies, are absolutely excluded from the tables. These 



