DOMINANT SPECIES VARY MOST 69 



species attain the rank of species. They may become extinct, 

 or they may endure as varieties for very long periods, as 

 has been shown to be the case by Mr. Wollaston with the 

 varieties of certain fossil land-shells in Madeira, and with 

 plants by Gaston de Saporta. If a variety were to flourish 

 so as to exceed in numbers the parent species, it w'ould then 

 rank as the species, and the species as the variety ; or it 

 might come to supplant and exterminate the parent species; 

 or both might co-exist, and both rank as independent species. 

 But we shall hereafter return to this subject. 



From these remarks it will be seen that I look at the term 

 species as one arbitrarily given, for the sake of convenience, 

 to a set of individuals closely resembling each other, and 

 that it does not essentially differ from the term variety, which 

 is given to less distinct and more fluctuating forms. The 

 term variety, again, in comparison with mere individual dif- 

 ferences, is also applied arbitrarily, for convenience' sake. 



WIDE-RANGING, MUCH DIFFUSED, AND COMMON SPECIES 



VARY MOST 



Guided by theoretical considerations, I thought that some 

 interesting results might be obtained in regard to the nature 

 and relations of the species which vary most, by tabulating 

 all the varieties in several well-worked floras. At first this 

 seemed a simple task ; but Mr. H. C. Watson, to whom I am 

 much indebted for valuable advice and assistance on this 

 subject, soon convinced me that there were many difficulties, 

 as did subsequently Dr. Hooker, even in stronger terms. I 

 shall reserve for a future work the discussion of these diffi- 

 culties, and the tables of the proportional numbers of the 

 varying species. Dr. Hooker 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 neces- 

 sarily here is with much brevity, is rather perplexing, and 

 allusions cannot be avoided to the "struggle for existence," 

 "divergence of character," and other questions, hereafter to 

 be discussed. 



Alphonse de Candolle and others have shown that plants 



