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 Rh CASUARINEÆ. The genus Casuarina is certainly not referable to any natural order of plants at present established; and its structure being now tolerably understood, it may be considered a separate order, as Mirbel has already suggested.

The maximum of Casuarina appears to exist in Terra Australis, where it forms one of the characteristic features of the vegetation. Thirteen Australian species have already been observed; the greater number of these are found in the principal parallel, in every part of which they are almost equally abundant; in Van Diemen's Island the genus is less frequent, and within the tropic it is comparatively rare; no species except Casuarina equisetifolia having been observed on the north coast of New Holland. Beyond Terra Australis only two species have been found, namely, C. equisetifolia, which occurs on most of the intratropical islands of the Southern Pacific, as well as in the Moluccas, and exists also on the continent of India; and C. nodiflora, which is a native of New Caledonia.

In the male flowers of all the species of Casuarina, I find an envelope of four valves, as Labillardière has already observed in one species, which he has therefore named C. quadrivalvis. But as the two lateral valves of this envelope cover the others in the unexpanded state, and appear to belong to a distinct series, I am inclined to consider them as bracteæ. On this supposition, which, however, I do not advance with much confidence, the perianthium would consist merely of the anterior and posterior valves, and these, firmly cohering at their apices, are carried up by the anthera, as soon as the filament begins to be produced, while the lateral valves or bracteæ are persistent; it follows from it also that there is no visible perianthium in the female flower, and the remarkable economy of its lateral bracteæ may, perhaps, be considered as not only affording an additional argument in support of the view now taken [572 of the nature of the parts, but also as in some degree again approximating Casuarina to Coniferæ, with which it was formerly associated.