tain instance of this, except Hippophae, already mentioned under Monoecia Tetrandria.
3. Trioecia. Of the only two genera which have ever been placed here, Ceratonia, Cavan. Ic. t. 113, belongs to Pentandria Monogynia. Ficus is so celebrated for the diversity of its flowers, as connected with the history of vegetable impregnation, see p. 336, that we are glad to take advantage of a trifling difference in the calyx of the two florets, (the barren one being most frequently three-cleft, the fertile five-cleft,) to keep it here.
All things being considered, this Class may be thought scarcely worth retaining. Yet as we know two or three genera entitled to a place in it, upon principles which the analogy of the two preceding Classes shows to be sound, we cannot tell but others may exist in the unexplored parts of the globe. For this reason, and for the uniformity of the system, I would venture to preserve it. If the 21st and 22d Classes should hereafter be reformed by some judicious and experi-