define this natural order, one of whose most remarkable characters consists in its unilocular ovarium, containing more than one, but always a determinate number of ovula, which are pendulous and attached to the apex of a central receptacle. This receptacle, which varies in its figure, in the different genera, in some being filiform, in others nearly filling the cavity of the ovarium, had not been previously noticed in any plant of the order.
The greater part of the Santalaceæ of Terra Australia are found in the principal parallel, to which several genera, namely, Leptomeria, Corethrum, and Fusanus are nearly limited: Santalum on the other hand is found chiefly within the tropic.
I have added Exocarpus and Anthobolus to this order, with certain genera of which they agree in habit and many points of structure, both of the flower and fruit: but they are readily distinguishable from the whole order by their fructus superus, and they may possibly differ also in the internal structure of their ovarium, which has not yet been satisfactorily ascertained.
The genus Exocarpus is most abundant in the principal parallel and southern parts of Terra Australis, but it is not unfrequent even within the tropic. Exocarpus cupressiformis is not only the most common species of the genus, but the most general tree in Terra Australis, being found in nearly the whole of the principal parallel, in every part of Van Diemen's Island that has been visited, and even within the tropic. I am acquainted with only three plants that have in that country an equally extensive range. These are Anthistiria australis, the most valuable grass as well as the most general plant in Terra Australis; Arundo Phragmitis, less frequent than the former, but which extends from the southern extremity of Van Diemen's Island to the North coast of New Holland; and Mesembryanthemum æquilaterale, which occurs on almost every part of the sandy sea shores, of both these Islands.
Exocarpus is not absolutely confined to Terra Australis, for Mr. Bauer has discovered a very remarkable species bearing its flowers on the margins of dilated foliaceous branches, analogous to those of Xylophylla; and Xylophylla longifolia, which was taken up by Linneus from Rumphius,[1]- ↑ Xylophyllos ceramica, Herb. amb. 7. p. 19. t. 12.
