50 ON THE ORIGIN OF SPECIES 



often give rise to varieties sufficiently well marked to 

 have been recorded in botanical works. Hence it is 

 the most flourishing, or, as they may be called, the 

 dominant species, — 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 modi- 

 fied, still inherit those advantages that enabled their 

 parents to become dominant 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 some- 

 what 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 inhabiting any country, shows that there 

 is something in the organic or inorganic conditions 

 of that country favourable to the genus ; and, conse- 

 quently, we might have expected to have found in 

 the larger genera, or those including many species, a 

 large proportional number 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 generally much more widely diffused 

 than plants higher in the scale ; and here again there 



