VARIATION UNDER NATURE 85 



at the common oak, how closely it has been studied; yet 

 a German author makes more than a dozen species out 

 of forms, which are almost universally considered by 

 other botanists to be varieties; and in this country the 

 highest botanical authorities and practical men can be 

 quoted to show that the sessile and pedunculated oaks 

 are either good and distinct species or mere varieties. 



I may here allude to a remarkable memoir lately pub- 

 lished by A. de Candolle, on the oaks of the whole world. 

 No one ever had more ample materials for the discrimi- 

 nation of the species, or could have worked on them 

 with more zeal and sagacity. He first gives in detail all 

 the many points of structure which vary in the several 

 species, and estimates numerically the relative frequency 

 of the variations. He specifies above a dozen characters 

 which may be found varying even on the same branch, 

 sometimes according to age or development, sometimes 

 without any assignable reason. Such characters are not 

 of course of specific value, but they are, as Asa Gray 

 has remarked in commenting on this memoir, such as 

 generally enter into specific definitions. De Candolle then 

 goes on to say that he gives the rank of species to the 

 forms that differ by characters never varying on the same 

 tree, and never found connected by intermediate states. 

 After this discussion, the result of so much labor, he 

 emphatically remarks: "They are mistaken 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 were founded upon a few speci- 

 mens, that is to say, were provisional. Just as we com© 

 to know them better, intermediate forms flow in, and 



