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In a contribution to the Philosophical Transactions of this Society, published in 1852 (Part II. p. 289), I gave an account of the internal anatomy of the stem or rhizome ofVictoria regia . I then stated that I regarded the arrangement of the vascular structures as essentially agreeing with that typical in Monocotyledons, and I directed attention to certain points of less importance, some of which appeared to strengthen the general argument in question, while others were opposed to it. Subsequently I have had an opportunity of studying the anatomy and development of the leaves, roots, and flowers ofVictoria , and of observing some interesting facts which have not been clearly made out in any of the various memoirs which have appeared on this subject. I have also been led to a reconsideration of the subject of the anatomy of the stem by a criticism which appeared in the ‘Flora Indica’ (p. 236), the distinguished authors of which, in their advocacy of the opinion that the Order Nymphæaceæ is really Dicotyledonous, question the agreement which I have declared to exist between the structure of the stems ofVictoria and of Monocotyledons. In the present paper, which may be regarded as a continuation and completion of the former, I shall first deal with the debated question of the structure of the rhizome, and afterwards give an account of the development of the appendicular organs, including the flower, and of the phenomena presented in the germination of the seed. For the abso­lute determination of the question whether a stem were organized on the Monocotyledonous or the Dicotyledonous type, it would be requisite first of all to define clearly what conditions we regard as typical in the two classes. This is no easy matter in the present state of our knowledge. The old terms Endogenous and Exogenous growth are founded on no corresponding contrast in the organization of the plants to which they refer. Exogenous growth is a reality, but endogenous growth is a figment of the imagination. The general distinctions between the stems of the two great classes of Angiospermous Flowering Plants depend upon a different mode of arrangement of the fibro-vascular bundles, and, usually, in addition to this, upon a different mode of arrangement of the elementary organs in the fibro-vascular bundles. These are the only essential differences; the formation of annual rings is by no means a constant phenomenon in perennial Dico­tyledons. It offers, however, a negative character for the Monocotyledons, since, from the construction and arrangement of their fibro-vascular bundles, they cannot produce annual (or periodical) rings of the same kind as those of the Dicotyledons. The layers formed in such exceptional instances asYucca, Dracæna , and analogous stems are totally different from those of the layers of Dicotyledons, being formed of entirely new fibro-vascular cords quite independent of those of the inner substance of the stem, while the successive layers of the stems of Dicotyledons are ordinarily horizontal developments from the cambium layers of the pre-existing bundles.

XXIV. On the anatomy of Victoria regia.―Part II