THE CARPEL 195 



Closure by Adnation to Receptacle. Carpels that stand obliquely on 

 the receptacle may be closed at the base by adnation of the margins to 

 the receptacle. In these carpels, the locule is enclosed, in part, by tis- 

 sues of the axis. Apparently, the ontogeny of these carpels has 

 not been described, but the adnation is pi-obably congenital. The 

 crescent-shaped carpel primordia and the primordium of the receptacle 

 develop together; the flanges of the carpel primordium arise united 

 with receptacular tissues. Higher up, the carpel margins unite with 

 each other. 



Closure by Connation. In some syncarpous gynoecia, carpels open at 

 the base are united by their lateral walls. Their locules unite, forming 

 a common ovarian chamber — Phytolacca, Sabal and other palms. This 

 type of gynoecium is part of the evidence that connation and adnation 

 were present in the gynoecium before the carpel closed; that the closed 

 carpel was not a character of the earliest angiosperms. 



Closure by Ontogenetic and Phylogenetic Fusion. The closure of the 

 carpel is commonly ontogenetic; the margins of a primordium, cres- 

 cent- or horseshoe-shaped in cross section, develop toward one another 

 and unite. But the closure may be congenital; the carpel arises closed 

 from a ring-shaped primordium. A primordium that is at first crescent- 

 shaped may become ring-shaped at the base and, with continuing 

 growth from the base, form a carpel that is closed distallv during 

 ontogeny but arises fused proximally. In many advanced families, the 

 carpel borders have become congenitally concrescent; the closed carpel 

 is phylogenetically established. (Failure to recognize the nature of the 

 ring-shaped carpel primordium has been largely responsible for the 

 peltate theory of basic carpel form.) A common comparable condition 

 in the corolla helps to make the complex carpel development clear. The 

 typical gamopetalous corolla arises from a whorl of separate primordia, 

 each representing one of the ancestrallv free petals. After elongation 

 has continued for some time, the petal primordia fuse into a ring, which 

 forms the corolla tube. The bases of the petals, evident by their inde- 

 pendent vascular supplies, are fused congenitally (or phylogenetically); 

 they arise fused. 



The Complex Carpel 



The differentiation of ovary, style, and stigma from the simple, primi- 

 tive carpel was a gradual one, which took place in many lines, with 

 elaboration of style and stigma proceeding at different rates. The stigma 

 is sometimes sessile, the style undeveloped in some of the Winteraceae 

 and Euptelea; the style may be well developed, the stigma still a primi- 

 tive stigmatic crest, decurrent on the style, as in Cercidiphylhim. Mor- 

 phologically, the style is usually the distal part of the primitive carpel. 



