Page:Journal of the Royal Geographical Society of London, Volume 1 (2nd edition).djvu/40

From Wikisource
Jump to navigation Jump to search
This page has been validated.
20
Sketch of the Botany of the Vicinity of Swan River.

the shores of which it was the only useful timber-tree, though there of very moderate size. I have named it Eucalyptus calophylla. Mr. Fraser describes it as forming, on the banks of the Swan, a large forest-tree, and erroneously refers it to Angophora, a genus which is limited to the east coast of New Holland. Other species of Eucalyptus, forming the timber of the country, are mentioned in the report, and considered to be some of the common gum-trees of Port Jackson, from which, however, I have no doubt they will prove to be distinct; for I am acquainted with no species of this genus common even to the east and south coasts of New Holland.

I shall conclude with a remark relating equally to the genus Eucalyptus and to the leafless Acaciæ, several species of which are found in the collection. This observation I have formerly made in the Appendix to Captain Flinder's Voyage in the following terms:
'These two genera are not only the most widely diffused, but by
'far the most extensive in Terra Australis, about one hundred of
'each having already been observed; and if taken altogether, and
'considered with respect to the mass of vegetable matter they con-
'tain, calculated from the size as well as the number of individuals,
'are perhaps nearly equal to all the other plants of that continent.
'They agree very generally also, though belonging to very different
'families, in a part of their economy, which contributes somewhat
'to the peculiar character of the Australian forests—namely, in
'their leaves, of the parts performing the function of leaves, being
'vertical, or presenting their margin, and not the surface, towards
'the stem, both surfaces have 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 folia-
'ceous petiole; while in Eucalyptus, where though very ge-
'neral, it is be 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 arboracent plants in a very few instances, as in several Coniferæ, they are confined to the upper surface.