THE CARPEL 225 



developed meristem. But the solitary ovule is unquestionably the high- 

 est type of placentation and the achene a reduced form of the follicle. 



Ontogeny shows the nature of the peltate carpel. In early develop- 

 ment, the typical carpel is like the leaf. The primordium arises as a 

 moundlike projection, which soon becomes crescent- or horseshoe- 

 shaped in cross section. If the primordium remains crescent- or horse- 

 shoe-shaped, the carpel formed is, under the peltate theory, "epeltate"; 

 if the basal meristem of the primordium extends laterally on the re- 

 ceptacle and becomes ring-shaped, the part of the carpel formed there- 

 after is tubular and the carpel is peltate. 



Epeltate carpels are closed ontogenetically; peltate carpels arise with 

 congenitally fused margins. From the standpoint of ontogeny, many 

 carpels are epeltate in early stages and become peltate in later stages. 

 Where the primordium becomes ring-shaped very early — fusion of the 

 margins is complete except at the carpel tip — the carpel is latent peltate, 

 with a cross zone "only suggested." The peltate carpel, tubular wholly 

 or in large part, developed from a ring-shaped primordium, is an ad- 

 vanced, not a primitive, type, in which fusion is phylogenetically estab- 

 lished. ( Similar congenital fusion is present in many parts of the plant. ) 



The various types of carpels described under the peltate theory are 

 shown by ontogeny to represent merely stages in the evolutionary 

 modification of the carpel. The epeltate carpel is a primitive carpel, 

 with closure ontogenetic; the peltate types are advanced, with closure, 

 at least in part, congenital; a ring-shaped meristem forms the tubular 

 part. Carpel closure may be wholly ontogenetic, wholly congenital, or 

 partly ontogenetic and partly congenital, but the peltate theory fails to 

 recognize congenital fusion. The "cross zone" represents the level in the 

 developing carpel between the distal part of the carpel, where closure 

 is ontogenetic, and the proximal part, where it is congenital. A ventral 

 longitudinal "strip" of the carpel wall is indeed formed by the section 

 of the basal meristematic ring between the edges of the originally 

 crescent-shaped primordium. But this strip is not delimited structurally; 

 it is initiated by basal growth, as is the rest of the carpel, not by a 

 cross-zone meristem, as implied by the peltate theory. This strip con- 

 sists of the marginal strips of the lamina, the fertile areas, but it is not 

 a distinct, morphologically significant part of the carpel. The "cross 

 zone" appears important in achenes where the carpel is shortened and 

 the ovules reduced to one, because the surviving ovule is attached at 

 this point, the remnant of the fertile, ventral border of the closed carpel. 



Ontogeny is claimed to support the peltate theory, in that the carpel 

 primordium "assumes very early the peltate form with the formation 

 of a cross zone." But this condition is demonstrated in achenes, where 



