48 On the Affinities of CcralophyUacccC, 



the micropyle. The correctness of this view is demonstrated 

 by a consideration of their internal structure. The embryo, 

 enclosed in a peculiar covering (the thickened and persistent 

 membrane of the nucule) lies in immediate contact with the 

 (organic as well as geometrical) base of the seed, the residue 

 of the cavity being filled with a rather firm albumen ; the radi- 

 cular extremity pointing from the hilum and towards the distant 

 micropyle. The seeds of Cabombaceae are therefore suspended 

 and ortliotropous, as in Ceratophyllaceae. 'The principal dif- 

 ference between the two orders, so far as respects the structure 

 of the ovule and seed, consists, therefore, in the less developed 

 embryo of the former being wholly enclosed in the persistent 

 sac of the nucule, (as in Nymphaeaceas), and in the presence of 

 albumen. It is evident, therefore, that the order Ceratophylla- 

 ceoe is almost as closely allied to Cabombaceae as to Nelum- 

 biaceas, and that it should stand in the immediate vicinity of 

 these two orders, notwithstanding the much lower develope- 

 ment of its floral organs, and other diversities attributable to its 

 wholly submersed habit. 



As to the affinity of the order Cabombaceae with Nelumbiaeea; 

 and Nymphasaceae, it may be remarked that it agrees with 

 the former in its innate anthers, apocarpous ovaries, and nearly 

 solitary ortliotropous seeds ; and with the latter in the presence 

 of albumen, and of a sac enclosing the embryo. It differs 

 from Nelumbiaceas chiefly in the albuminous seeds, and less 

 developed embryo, and in the absence of an enlarged torus ; 

 while Nymphoeaceoe, however close the alliance, are essentially 

 distinguished from both these families by their adnate anthers, 

 polyspermous and syncarpous ovaries, and anatroyous seeds.* 



* In both Nymphaeacca: and Cabombaceae the embryo is commonly 

 described as situated nearly without the albumen, at the base of the 

 seed : there is, however, this important difference, that in the latter the 

 embryo is placed at the true base of the seed, i. e. next the chalaza ; 

 while in the former (as in Papaveraceae, &c.) it is situated at th« ex- 



