character of the Australian forests, namely, in their leaves, or the parts performing the functions of leaves, being vertical, or presenting their margin, and not either surface, towards the stem: both surfaces having consequently the same relation to light.
"This economy, which uniformly takes place in the Acaciæ, is in them the consequence of the vertical dilatation of the foliaceous footstalk; while in Eucalyptus, where, though very general, it is by no means universal, it proceeds from the twisting of the footstalk of the leaf."
To this quotation it may be added that these two genera still more uniformly agree in the similarity of the opposite surfaces of their leaves. But this similarity is the indication of a more important fact—namely, the existence equally on both surfaces of the leaf, of those organs, for which, as I believe them to be in general imperforated, I have adopted the name of cutaneous glands, but which by most authors are denominated pores, or stomata of the epidermis.
In leaves, especially of trees and shrubs, these glands are generally found on the under surface only; while among arborescent plants in a very few instances, as in several Coniferæ, they are confined to the upper surface.
21] In addition to the two extensive New Holland tribes here mentioned, there are many other cases in which these organs occupy both paginæ; and I am inclined to think such cases more frequently occur on that continent than in any other part of the world. It is at least certain that on this microscopic character, of the equal existence of cutaneous glands on both surfaces of the leaf, depends that want of lustre which is so remarkable in the forests of New Holland.
