48 DOMINANT SrECIES VARY MOST. 



difficulties, and the tables of the proportional numbers of 

 the varying species. Dr. Hooper permits me to add that 

 after having carefully read my manuscript, and examined 

 the tables, he thinks that the following statements are 

 fairly well established. The whole subject, however, treated 

 as it necessarily here is with much brevity, is rather per- 

 plexing, and allusions cannot be avoided to the " struggle 

 for existence," " divergence of character," and other ques- 

 tions, hereafter to be discussed. 



Alphonso de Candolle and others have shown that plants 

 which have very wide ranges generally present varieties ; 

 and this might have been expected, as they are exposed to 

 diverse physical conditions, and as they come into competi- 

 tion (which, as we shall hereafter see, is an equally or more 

 important circumstance) with different sets of organic beings. 

 But my tables further show, that, in any limited coun- 

 try, the species which are the most common, that is, abound 

 most in individuals, and the species which are most widely 

 diffused within their own country (and this is a different 

 consideration from wide range, and to a certain extent from 

 commonness), oftenest 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, are the 

 most diffused in their own country, and are the most numer- 

 ous in individuals — which oftenest produce well-marked vari- 

 eties, 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 more likely 

 to yield offspring, which, though in some slight degree 

 modified, still inherit those advantages that enabled their 

 parents to become dominant over their compatriots. In 

 these remarks on predominance, it should be understood 

 that reference is made only to the forms which come into 

 competition with each other, and more especially to the 

 members of the same genus or class having nearly similar 

 habits of life. With respect to the number of individuals, 

 or commonness of species, the comparison of course relates 

 only to the members of the same group. One of the higher 

 plants may be said to be dominant if it be more numerous 

 in individuals and mpre wic^ly diffused than the other 

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