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Show 52 V .A.RIETIES GRADUATE INTO SPECIES. CHAP. II. strongly marked and more permane~t varieties; and. at these latter, as leading to sub-species, and to t~peCie~ The passage from one stage of difference to anol ~r ~~ hi her stage may be, in some cases, d~e mere ! . o . e g . d t' of different physwal conditions In lona-continue ac wn · h · twoo different regions ; but I have not much. fait In th . . . and I attribute the passage of a variety, from IS VIeW , · 1 f 't t a state in which it differs very shght y r?m Is paren to one I.n wh ic h I't di' ~11e1 rs more to the action of natural ' selection in accumulating (as will her~after be :more fu~ly explained) differences of structure In cert~In definite direetions. Hence I believe a well-marked variety.may ?e justly called an incipient species ; but whether th1~ behef be justifiable must be judged of by the general ~·eight of the several facts and views given throu?h?ut thi.s ~o::k. It need not be supposed that all varieties or Incipient species necessarily attain the rank of sp~cies. They may whilst in this incipient state become ext:nct, or they may endure as varieties for very long penods,. as has be~n shown to be the case by Mr. Wollaston with the v~neties of certain fossil land-shells in Madeira. If a varwty were to flourish so as to exceed in numbers the parent species, it would then rank as the species, and the species as the variety ; or it might come to ~upplant a_nd exterminate the parent species; or both might co-exist, and both rank as independent species. But we shall hereafter have to return to this subject. From these remarks it will be seen that I look at the term species, as one arbitrarily given for the sak~ 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 distin?t a~d more fluctuating forms. The term variety, again, Ill co~parison with mere individual di~erences, is also apphed arbitrarily, and for mere convenience sake. DOMINANT SPECIES V .A.RY MOST. 53 Gui.ded 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; bnt Mr. H. 0. 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 my future work the discussion of these difficulties, and the tables themselves 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 necessarily 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. Alph. De Candolle and others have shown that plants which have very wide ranges generally present varieties ; and this might have been expected, as they become exposed to diverse physical conditions, and as they come into competition (which, as we shall hereafter see, is a far more important circumstance) with different sets of organic beings. But my tables further show that, in any limited country, the species which are 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), 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,- |