characters : by the involucrum for example Malva and Althea are principally distinguished. The principal distinguishing characters between Hibiscus and Abelmoschus appertain to the calyx, in the former its segments are distinct, while in the latter they continue to adhere, presenting the form usually called spathaceous, that is, splitting along one side only, like a spathe. The carpels being many or few seeded, afford subsidiary characters, but that taken from the calyx is essentially the distinguishing one, as many species of Hibiscus have carpels with a plurality of seeds, but few, if any, have the spathaceous calyx. Upon the whole however, I think there is reason to doubt the propriety of breaking down even very large genera on such grounds. Abutilon and Sida, which want the involucrum and were formerly united, have on somewhat similar, but much better grounds, been separated. In Abutilon the carpels are membranacious or bladdery, and contain several seeds : in Sida they are l-seeded, usually coriacious, and furnished at the apex with a double beak. Thespesia is separated from Hibiscus on account of its truncated undivided calyx, resembling (he cup of an acorn, and Paritium on account of its imperfectly 10-oelled capsule, caused by the bending inwards of the margins of the valves.
It seems questionable whether it is judicious to take leading generic characters from the involucrum, Linnaeus objected to the principle, and laid it down as a rule, that they ought always to be taken from the fructification only, by which he meant the calyx and organs embraced by it ; but in the case of the Malvaceceœ, nearly all of which are referable to his class and order Monadelphia polyandria, and also in Umbelliferœ , he found it convenient to depart from his own rule, and got over the difficulty by calling the involucrum an external calyx. Dr. Zenker has, (Plantæ Indicæ) in his genus Hymenocalyx, our Abelmoschus angulosus, carried this departure from the Linnean rule to excess, by founding a genus on the circumstance of the involucrum as well as the calyx occasionally splitting spathaceously, for with that exception, which I have since ascertained is not constant, there is absolutely no difference between that genus and Abelmoschus, and ought not in my opinion, to be retained.
The spathaceous involucrum of that species which completely conceals the calyx, led Mr. Arnott and myself into a curious error, by inducing the belief that it was the calyx, and that the involucrum was so early caducous that we had no opportunity of describing it.
The genus Dyctiocarpus which associates with Sida in wanting the involucrum, and in having l-seeded carpels, I ventured to separate on account of its definite stamens, which had previously caused it to be removed from the order and referred to Byttneriaceœ. The curiously reticulated testa of its seed affords another good character, as being one which I am not aware of existing in any other species of the order. The genus Decaschistia is remarkable for its 10-celled and 10-valved, capsule, with a solitary seed in each cell. For further illustrations of the several genera of this rather large and complex order, I must refer to my Icones, with the aid of which, I hope to be able to afford most ample illustrations of the genera of all the larger and more important orders to be treated of in the course of this work.
The following additions have been recently made to the order.
Urena repanda — Of this little known species I have at length got specimens, from Goomsoor (unfortunately rather imperfect,) through the kindness of W. G. Davidson, Esq. I find it does not correspond very accurately with the generic character of Urena : neither does the specimen agree well with the character of the species, but as the species of this genus are apt to vary considerably in their forms I have no doubt of its being the same plant, as it agrees in one or two important points. These peculiarities lead to the suspicion that it ought to be removed from the genus, though in habit it associates very closely. The most prominent features of distinction between this and the other species of the genus consists in its having both the involucel and calyx campanulate, 5-cleft, or rather toothed at the apex, and completely enclosing the carpels, which, in place of being globose and armed all over with hooked prickles, as in the rest of the genus, are only slightly convex exteriorly, and nearly triangular. The very distinct form and large size, as compared with the rest of the genus, of the involucel and calyx, added to the different shape, and glabrous exterior of the carpels, lead to the supposition that it ought to form a separate genus. The habit however, and the peculiar reticulation of the leaves, which coincide exactly with some other species of Urena, induce me for the present to leave it as a doubtful member of that genus, the more so as my specimens are in fruit only. The leaves in them are nearly round, slightly acuminated at the point, cordate at the base, repandly dentate on the margin, and pubescent on both sides with a single gland beneath ; the flowers numerous, the peduncles axillary several flowered, and from the abortion of the leaves, racemose towards the ends of the branches.
Though my specimens are imperfect, yet as this plant is very little known, I shall endeavour to have it figured in my Icones,
