and on the Structure of Hydnora africana. 229 



indication of a channel connecting it with the surface of the albumen, in the 

 centre of which it is seated. 



In Cytinus, in which I believe I have at length found ripe fruits, the seeds 

 are extremely minute, and generally retain at their base the bipartite mem- 

 brane more distinctly observable in the unimpregnated ovulum. To this 

 membrane the name of arillus may be given ; but it may also, and, perhaps, 

 with greater probability, be considered the imperfect production of the testa 

 or outer membrane. 



The seed itself is elliptical, with a slight inequality at top indicating the 

 depression or perforation observable in the ovulum. The single integument of 

 the seed is easily separable from the nucleus, and by moderate pressure splits 

 longitudinally and with great regularity into two equal portions ; in texture 

 it is a crustaceous membrane, indistinctly reticulate, the areolae, when very 

 highly magnified, appearing to be minutely dotted with a semi-opake centre. 



The nucleus, corresponding exactly in size and form with the integument, 

 has its surface also reticulate, but the areolae are not dotted ; and it appears, 

 as far as I can ascertain in so minute a body, to consist of a uniform cellular 

 tissue, very exactly resembling the nucleus of an Orchideous plant. 



The result of the comparison now made, and which might be extended to 

 other points of structure of Rafflesia, Brugmansia, Hydnora and Cytinus, seems 

 to be, that these four genera, notwithstanding several important differences, 

 form a natural family to which the name of Rafflesiace^ may be given ; and 

 that this family is again divisible into three tribes or sections : 



The first, Rafflesiece, consisting of Rafflesia and Brugmansia, is distinguish- 

 able by the ovarium being either in part or wholly superior to the origin of the 

 calyx, in its composition or internal structure, in the placentation and direc- 

 tion of the ovula, in the structure of the seed and in that of the antherse. 



The second section, Hydnorece, formed of Hydnora alone, is characterized 

 by its completely adherent ovarium, singularly divided stigmata, the peculiar 

 origin and structure of its pendulous placentae, its embryo inclosed and seated 

 in the centre of a dense albumen, and by the arrangement and structure of its 

 antherae. 



In the third section, or Cytinece, the placentae are parietal, the ovarium is 



2 H 2 



