Chap. II.] SPECIES OF LARGER GENERA VARIABLE. 69 



small majority on. the side of the larger genera. I will 

 here allude to only two causes of obscurity. Fresh- 

 water and salt-loving plants generally have very wide 

 ranges and are much diffused, but this seems to be 

 connected with the nature of the stations inhabited by 

 them, and has little or no relation to the size of the 

 genera to which the species belong. Again, plants low 

 in the scale of organisation are 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, circum- 

 stances have been favourable for variation; and hence 

 we might expect that the circumstances would generally 

 be still favourable 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 hav- 

 ing 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, 



