i2i8 A TEXTBOOK OF THEORETICAL BOTANY 



consequently non-septate, the folds do not extend but become directly 

 transformed into placentae. 



Where the receptacle has a particularly broad apex, as in Caryophyllaceae 

 and Phytolaccaceae, the carpels may arise as a whorl of horseshoe-shaped 

 loops around the periphery of the receptacle, to which their ventral margins 

 are joined from the beginning, and the receptacle persists as the axis of the 

 mature ovary, to which the placentae are fused. 



The Nymphaeaceae afford particularly interesting examples of this 

 arrangement. In Cahomba and Nelumbium, the carpels are free, but in the 

 latter genus they become embedded in an obconical development of the 

 receptacle, only the stigmas being left visible. In Victoria a single whorl of 

 carpels is formed around the receptacle, leaving its apex free, which sticks up 

 nakedly in the centre of the flower. The base of the receptacle is expanded 

 into a cup, enclosing the carpels, which are fused to it by their dorsal walls. 

 The divisions between the individual carpels are, however, clearly marked 

 on their ventral surfaces. In Nymphaea and Nuphar the receptacular cup 

 has closed in towards the axis, thus causing the ventral sides of the carpels 

 to adhere to the apex of the receptacle, so that it now forms the axis of the 

 gynoecium. The carpels in this apparently coenocarpous gynoecium of 

 Nymphaea are not completely coherent, but are separated by narrow sinuses. 

 In Nuphar these are absent and the ovary appears to be truly compound, 

 but it differs from that of Nymphaea in being seemingly superior. That the 

 outer wall of the ovary is, however, really receptacular is shown by two 

 phenomena. About 20 per cent, of the stamens in Nuphar, and all the 

 stamens in Nymphaea, arise from this outer wall, which is one indication of 

 its receptacular character. The matter is rendered certain, however, by the 

 behaviour of the fruit of Nuphar. It is detached at maturity and floats; 

 the inner tissues of the ovary wall become highly turgescent and expand, 

 causing the enclosing coat to split into lobes, which bend outwards, reveal- 

 ing the true carpels. The interstitial tissue between the carpels disinte- 

 grates and they separate as individuals. Despite their enclosure by the 

 receptacular cup, they have never, in fact, lost their individuality. 



All the carpels of the above family, with the exceptions of Victoria and 

 Euryale, arise from peltate primordia; they are, in fact, pouch-like carpels, 

 and they retain their pouch-like character throughout, having no suture and 

 a stigmatic surface all round the lip of the pouch. This is uncommon, but is 

 seen also in ZannicheUia among the Helobiae, which has peltate carpels with 

 peltate stigmas. In the majority of carpels which have peltate primordia, 

 the dorsum extends much above the ventral portion and forms a condu- 

 plicate sac, whose margins join in the ventral line to form a suture and bear 

 the stigmatic surfaces. Thus only the lower part of the carpel is truly 

 pouch-like. This is the semi-peltate type already mentioned. In the 

 earlier stages, however, there is a great measure of similarity between these 

 peltate structures. The carpel of Ceratophyllum, for instance, closely 

 resembles, in its early stages, that of Nehimhium, a matter of systematic 

 interest in view of the disputed relationship of the former genus. 



