XXI.—On Leaf-Architecture as illuminated by a Study of Pteridophyta

Abstract

The expression “architecture” as applied to the leaf was introduced by Prantl in his monograph on the Hymenophyllaceæ. It may be adopted as connoting the sum of the facts of construction of leaves; together with those principles or methods deduced from them, upon which we find the leaf to be built up. The varieties of size, form, and complexity of leaves appear infinite; but similarities in the scheme of their construction are obvious. It cannot be assumed that where similarities occur they are necessarily due to immediate community of descent. They may or may not be. Parallel development under similar conditions may be, and probably has been often, the source of such similarity. But even so it may be possible to connect the simpler and the more complex within the several lines of nearer relationship, and a study of several such lines may be expected to disclose certain underlying principles or methods which have ruled in the construction of foliar organs at large. The recognition of these, in their evolutionary aspect, is the proper basis for a scientific knowledge of leaf-architecture.