CHARACTERS AS ADAPTIVE AND SPECIFIC (_concluded_). Our subject is not yet exhausted. For it remains to observe the consequences which arise from the dogma of utility as the only _raison d'être_ of species, or of specific characters, when this dogma is applied in practice by its own promoters. * * * * * Any definition of "species"--excepting Nos. 1, 2, and 5, which may here be disregarded--must needs contain some such phrase as the one with which Nos. 3 and 4 conclude. This is, that peculiar characters, in order to be recognized as of specific value, must present neither more nor less than "some certain degree of distinctness." If they present more than this degree of distinctness, the form, or forms, in question must be ranked as generic; while if they present less than this degree of distinctness, they must be regarded as varietal--and this even if they are known to be mutually sterile. What, then, is this certain degree of distinctness? What are its upper and lower limits? This question is one that cannot be answered. From the very nature of the case it is impossible to find a uniform standard of distinction whereby to draw our boundary lines between varieties and species on the one hand, or between species and genera on the other. One or two quotations will be sufficient to satisfy the general reader upon this point. Mr. Wallace himself alludes to "the great difficulty that is felt by botanists in determining the limits of species in many large genera," and gives as examples well-known instances where systematic botanists of the highest eminence differ hopelessly in their respective estimates of "specific characters." Thus:-- "Mr. Baker includes under a single species, Rosa canina, no less than twenty-eight named varieties distinguished by more or less constant characters, and often confined to special localities, and to these are referred about seventy of the species of British and continental botanists. Of the genus Rubus or bramble, five British species are given in Bentham's _Handbook of British Flora_, while in the fifth edition of Babington's _Manual of British Botany_, published about the same time, no less than forty-five species are described. Of willows (Salix) the same two works enumerate fifteen and thirty-one species respectively. The hawkweeds (Hieracium) are equally puzzling, for while Mr. Bentham admits only seven British species, Professor Babington describes no less than seventy-two, besides several named varieties[125]." [125] _Darwinism_, p. 77.