Look 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 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.