62 



DOUBTFUL SPECIES. ' [Chap. II. 



animal or plant in a state of nature be highly useful to 

 man, or from any cause closely attracts his attention, 

 varieties of it will almost universally be found recorded. 

 These varieties, moreover, will often be ranked by some 

 authors as species. Look at the common oak, how close- 

 ly 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 

 published by A. de Candolle, on the oaks of the whole 

 world. No one ever had more ample materials for the 

 discrimination 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 labour, he 

 emphatically remarks: "They are mistaken, who 

 repeat that the greater part of our species are clearly 



