THE ANGIOSPERMAE 1219 



Just as some foliage leaves which have a pouch-zone at the base of the 

 lamina do not retain the peltate form as they develop, so the semi-peltate 

 carpels only show a true, unsutured pouch in their earlier, lower portions. 

 Peltation in leaves is associated with a unifacial, i.e., centric, structure in 

 their petioles; similarly centric structure is characteristic of the gynophore 

 stalks of peltate carpels. 



The tvpe of carpel with a peltate primordium and a marked ventral 

 sill, such as those of many Ranunculaceae, is generally uniovulate, with the 

 ovule borne medianly on the ventral sill, the dorsal portion of the carpel 

 being sterile. Uniovulate carpels are exceptional in syncarpous ovaries 

 and when they are pluriovulate it is the carpel margins which are fertile and 

 extend almost the whole length of the carpel. The sill in such carpels is 

 sterile and much reduced or even sunk in the tissue of the receptacle apex. 

 Uniovulate peltate carpels do sometimes, nevertheless, compose syncarpous 

 ovaries, notably in the Umbelliferae, where the tissue between the joined 

 carpels originates as a combination of the ventral sills of the carpels, which 

 extend upwards unitedly from the base during development and mature 

 a single median ovule on each side. 



It is evident from what has been said above that carpels are, in origin, 

 of at least two kinds, those showing a peltate and those showing a folded or 

 condupHcate mode of development. Theories of the morphological nature 

 of the carpel should take cognizance of these differences and they should 

 be remembered if one adopts any particular view. There is also the further 

 possibility that the carpel may have been evolved along more than one line 

 of descent from the immediate progenitors of the Angiosperms, despite the 

 many other characters which seem to link them into a unitary group. 



The inferior ovary is a structure about which much controversy has 

 centred. To nineteenth-century botanists, working on the theory of the 

 flower as a metamorphosed shoot, it seemed self-evident that epigyny had 

 been derived from hypogyny and that perigyny was an intermediate con- 

 dition. This presumed succession is exemplified within the limits of 

 several distinct families, notably the Rosaceae and Saxifragaceae, while a 

 number of families of very different affinities, e.g., Onagraceae, Umbelli- 

 ferae, Vacciniaceae and Orchidaceae, are characterized by predominant 

 epigyny, which suggests that the condition has arisen independently in 

 several lines of descent. 



It was perhaps natural that the first view to be propounded about 

 epigyny was that it was due to the w-ell-known phenomenon of adnation, 

 the carpels being supposedly enclosed by the coalescence of the outer floral 

 parts among themselves and with the conjoined carpels. This theor}^ 

 orginated with A. P. de Candolle and was strongly supported by Van 

 Tieghem. Towards the end of the century it lost ground to the " axial " 

 theories. The cup in perigynous flowers seldom shows any external evidence 

 of being a compound structure and the idea arose with Schleiden that it was 

 a hollow axial upgrowth. In Schleiden's original view, the carpels as well 

 as the other parts were upborne upon the margin- of the cup; the carpels 



