Mr. J. Miers on the Affinities of the Icacinacese. 219 



sion. Proceeding upon the principle, that the most scientific 

 basis for the distribution of plants is that founded on the cha- 

 racters which from their nature must be the most invariable, 

 I mean those offered by the development of the organs of repro- 

 duction, we perceive a feature of most general occurrence, where 

 the margins of the carpellary leaves are supposed to become pla- 

 centiferous : sometimes these are believed to unite either by their 

 edges and thus to form parietal placentations, or by the variable 

 degree of their inflexion, to constitute either loculigerous or 

 axile placentations ; and from the evidence I shall be able to show, 

 it will be evident that it is among the latter we must seek a 

 place for the Icacinacete. But I have suggested the existence of 

 several families, now distributed unsatisfactorily in different parts 

 of the system, where we must imagine the placentas to have 

 originated, not from the margins of carpellary leaves which in 

 such cases may be considered as sterile, but where their ovuli- 

 gerous development is to be traced from the more basal or 

 petiolar portions of the carpellary leaves : under this point of 

 view, we may reconcile the idea of the original formation of an 

 ovarium, winch, though constituted of several carpels, will some- 

 times be unilocular, and at other times often incompletely pluri- 

 locular at the base, while in every instance they are all invariably 

 1-celled at the summit, the ovules being always attached to an 

 erect placenta arising from the base of the cell, and completely 

 unconnected with the style. This extensive group I have pro- 

 posed to associate together in a distinct class, the Cionosperma 

 (huj. op. vii. p. 207). 



It will be in vain to urge, that there exists only a slight dif- 

 ference in the structure of the plurilocular ovarium with axile 

 placentation, and the one-celled ovary with central placentation : 

 this has been contended by several able botanists, who have 

 argued that in such cases the dissepiments have been originally 

 complete, but that by their attenuation they have broken away, 

 until they have left the placentary column free. I do not deny 

 that under certain circumstances this sometimes happens, but in 

 such cases we can always trace the indications of such rupture, 

 and we also invariably find, that the axile column, rendered thus 

 free in the middle, is always attached by its summit to the style. 

 On the other hand, in Mijrsinacea, we cannot discern any indica- 

 tion of parietal expansion, or the smallest involution of what we 

 may conceive to have been the sterile margins of the carpellary 

 leaves; we find there the ovules often crowded around a free 

 globular placenta, rising but little above the base of the cell, and 

 springing directly from the pedicel of the flower : here, at least, 

 we have fair evidence, that both placentae and ovules must have 

 - proceeded from an immediate expansion of the elementary petioles 



