allied to the Natural Order Burmanniaceæ. 549 
doubt; but it appears to me, that if we adopt the principle on which Aposta- 
sie have been separated from Orchidee and Ayridece from Restiaceæ, 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 Apteriacee ; but if, on the contrary, the difference 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 Burmanniacec, 
giving to the first section the title of Burmanniew, and to the second that of 
Apterieæ. 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 Gentianeæ, 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 placentæ. Mr. Brown has clearly demonstrated 
the structure of the ovarium of Orchidew 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 Pleurothallis, though in most other Orchidec the structure of the 
walls is very reticulate. In Orchideæ, the thick fleshy substance which fills 
4c2 
