. The vegetable kingdom : or, The structure, classification, and uses of plants, illustrated upon the natural system. oken whorl. Buttheir most exact difference from the other Orders of the Alliance consists in the singu-lar structure of their placenta, which expands into hard woody processes, which aremost commonly hooked. In the form of their embryo they agree AA-ith Bignoniads, butthe cotyledons are more fleshy, and their seeds are never winged. From Figwortsthey are absolutely divided by the absence of albumen, as well as by theu placental pro-cesses and large fleshy cotyledons. A singular
. The vegetable kingdom : or, The structure, classification, and uses of plants, illustrated upon the natural system. oken whorl. Buttheir most exact difference from the other Orders of the Alliance consists in the singu-lar structure of their placenta, which expands into hard woody processes, which aremost commonly hooked. In the form of their embryo they agree AA-ith Bignoniads, butthe cotyledons are more fleshy, and their seeds are never winged. From Figwortsthey are absolutely divided by the absence of albumen, as well as by theu placental pro-cesses and large fleshy cotyledons. A singular want of development occms in thecalyx of the genera Thunbergia, Mendozia, and Clistax, in which that organ is some-times reduced to a mere obsolete ring, its place being suppHed by bi*acts. Mendozia isalso remarkable for its fruit being a 1-seeded drupe, with crumpled clirysaloid coty-ledons. Mr. Bentham states that the placental processes are sometimes absent; in suchcases the embryo can be alone relied upon. Fig. CCCCLYIII.—Nelsonia campestris. 1. flowers ; 2. pistil; 3. capsule; 4. cross section of a Fig. CCCCLVIII. BiGNOMALES.] ACANTHACE^. 679 An elaborate account of this Order has been published by Professor Nees v. Esenbeck,in his Dissertation upon the Indian species of Dr. Wallichs Herbarium, in the work abovequoted. It is there that tlie mass of genera was first revised, their limits investigated,and a natm-al arrangement of them proposed. This eminent Botanist adopts the opinionof Dr. Brown, that among Acanthads the most valuable of all characters resides in theplacental processes, and accordingly his three great tribes are defined thus:—I. Thun-hergiecB: Processes expanded into a horny cup and adnate to the seed, which they NeUoniecB : Processes contracted into a papilla which bears (not carries) the small and pitted. III. Echmatacanthi: Seeds supported by hooked suboidinate cli\isions are formed upon considerations con
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