84 Prof. A. Gray on Species considered as to 



/era, Q. acutifolia, &c. have the leaves sometimes entire and some- 

 times toothed, upon the same hranch, or present transitions from one 

 tree to another, I might readily have united my Q. Tlapuxahuensis 

 to Q. Sartorii of Liebmann, since these two differ only in their entire 

 or their toothed leaves. From the fact that the length of the peduncle 

 varies in Q. robur and many other Oaks, I might have combined 

 Q. Seemanni, Liebm., with Q. salicifolia, Nees, I have not admitted 

 these inductions, but have demanded visible proof in each particular 

 case. Many species are thus left as provisional ; but in proceeding 

 thus, the progress of the science will be more regular, and the syno- 

 nymy less dependent upon the caprice or the theoretical opinions of 

 each author." 



This is safe and, to a certain degree, judicious, no doubt, as 

 respects published species. Once admitted, they may stand 

 until they are put down by evidence, direct or circumstantial. 

 Surely a species may rightfully be condemned on good circum- 

 stantial evidence. But what course does DeCandolle pursue in 

 the case, of every-day occurrence to most working botanists 

 having to elaborate collections from countries not so well ex- 

 plored as Europe, when the forms in question, or one of the 

 two, are as yet unnamed ? Does he introduce as a new species 

 every form which he cannot connect by ocular proof with a near 

 relative from which it differs only in particulars which he sees 

 are inconstant in better-known species of the same group ? We 

 suppose not. But if so, little improvement for the future upon 

 the state of things revealed in the following paragraph can be 

 expected. 



" In the actual state of our knowledge, after having seen nearly 

 all the original specimens, and in some species as many as 200 

 representatives from different localities, I estimate that, out of 

 the 300 species of Cupuliferce which will be enumerated in the ' Pro- 

 dromus,' two-thirds at least are provisional species. In general, 

 when we consider what a multitude of species were described from 

 a single specimen, or from the forms of a single locality, of a 

 single country, or are badly described, it is difficult to believe that 

 above one-third of the actual species in botanical works will remain 

 unchanged." 



Such being the results of the want of adequate knowledge, 

 how is it likely to be when our knowledge is largely increased ? 

 The judgment of so practised a botanist as DeCandolle is im- 

 portant in this regard ; and it accords with that of other botanists 

 of equal experience. 



" They are mistaken,^' he pointedly asserts, " who repeat that 

 the greater part of our species are clearly limited, and that the 

 doubtful species are in a feeble minority. This seemed to be 

 true so long as a genus was imperfectly known, and its species 



