allied to the Natural Order Burmanniacese. 549 



doubt ; but it appears to me, that if we adopt the principle on which Aposta- 

 siece have been separated from Orchidece and Xyridece from Restiacece, we 

 are bound to class the second section as distinct from the first. If this view 

 be admitted, I should propose to adhere to the suggestion offered by me in 

 1837, to arrange these new genera into a separate family, which might be 

 called Apteriacece ; but if, on the contrary, the diflFerence of structure of the 

 ovarium be not thought a distinction of sufficient importance to warrant their 

 separation into two families, they must then be associated with Burmanniacece, 

 giving to the first section the title of Burmanniece, and to the second that of 

 Apteriece. But I fear that the former view, which at first sight would seem to 

 rest on a wide and well-founded distinction, will on mature consideration be 

 found of less value, since the extensive order of Gentianece, for instance, 

 presents many instances of gradual transition, beginning with the unilocular 

 capsule with parietal placentation, the margins of the valves being ovuliferous, 

 and ending in complete central placentation and a bilocular fruit, showing 

 numerous cases of intermediate degrees of inflection of the ovuliferous mar- 

 gins. 



The only other observation that I shall add respecting these plants relates 

 to the striking resemblance of their seeds with those of most orchideous 

 plants, and the similarity in texture and structure of the pericarpium, which 

 in both families will be found to consist of a series of closely-packed trans- 

 verse ribs, seldom interrupted, proceeding from the intermediate lines where 

 dehiscence takes place, to the placentae. Mr. Brown has clearly demonsti-ated 

 the structure of the ovarium of Orchidece to consist of three carpellary leaves 

 united by their ovuliferous inflected margins. In Dictyostega a similar struc- 

 ture is evident, only that the margins are not inflected, but are directly united 

 by their edges, where they appear to be conjoined by an intervening, opake, 

 reticulated line, running from the base to the apex, and forming a support to 

 the horizontal, transverse, crowded ribs that compose the walls of the ovarium ; 

 immediately within this line is a compact bundle of longitudinal fibres forming 

 the placenta, upon which the numerous closely imbricate ovula are attached. 

 The same structure of the walls of the ovarium is especially visible in many 

 species of PleurothalUs, though in most other Orchidece the structure of the 

 walls is very reticulate. In Orchidece, the thick fleshy substance which fills 



4 c 2 



