54 DOMINANT SPECIES VAKY MOST. Chap. II. 



those which range widely over the world, are the most 

 diffused in their own country, and are the most numerous 

 in individuals, — which oftenest produce well-marked 

 varieties, or, as I consider them, incipient species. And 

 this, perhaps, might have been anticipated ; for, as 

 varieties, in order to become in any degree permanent, 

 necessarily have to struggle with the other inhabitants 

 of the country, the species which are already dominant 

 will be the most likely to yield offspring which, though 

 in some slight degree modified, will still inherit those 

 advantages that enabled their parents to become domi- 

 nant over their compatriots. 



If the plants inhabiting a country and described in 

 any Flora be divided into two equal masses, all those in 

 the larger genera being placed on one side, and all those 

 in the smaller genera on the other side, a somewhat 

 larger number of the very common and much diffused or 

 dominant species will be found on the side of the larger 

 genera. This, again, might have been anticipated ; for 

 the mere fact of many species of the same genus in- 

 habiting any country, shows that there is something in 

 the organic or inorganic conditions of that country 

 favourable to the genus ; and, consequently, we might 

 have expected to have found in the larger genera, or 

 those including many species, a large proportional num- 

 ber of dominant species. But so many causes tend to 

 obscure this result, that I am surprised that my tables 

 show even a 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 have 

 generally 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 



