194 MORPHOLOGY OF THE ANGIOSPERMS 



day of open carpels in unrelated taxa and the undoubted occurrence of 

 independent closure in several or many phylogenetic lines. (Outstand- 

 ing among the contributions of comparative morphology is the dis- 

 covery of the frequent occurrence in phylogenetic progress of the same 

 structural modification — dioecism, gamopetaly, zygomorphy, the in- 

 ferior ovary, the solitary ovule, the vessel.) The carpel is closely like 

 the leaf in many ways. In vernation, the leaf is folded or rolled in sev- 

 eral ways: conduplicate, involute, revolute. In ecological modification, 

 the leaf blade may, under reduction, be folded or rolled upward or 

 downward, and no type apparently is basic to the others. It would be 

 strange, in the light of the behaviour of the leaf in vernation and in 

 ecological modification, if the carpel, so like the leaf in form, ontogeny, 

 and anatomy, closed in only one way — that all forms of closed carpels 

 have been derived from the conduplicate type. 



That the closed carpel is not an ancient angiosperm character is evi- 

 dent not only in the presence of open carpels, even in some fairly ad- 

 vanced families, and the frequent presence of those with borders merely 

 appressed, but also in the presence of carpels closed by adnation to 

 the receptacle. Fusion, by both connation and adnation, clearly pre- 

 ceded closure of the carpel. 



Position, number, and size of ovules may, in part, determine method 

 of enclosure. Conduplicate closing perhaps provides better enclosure 

 where there are many ovules scattered over the lamina; involute, better 

 space for ovules massed in longitudinal rows near the margins. Carpels 

 that are clearly conduplicate usually have laminar or sublaminar 

 placentation — an association of primitive characters, but not necessarily 

 evidence that involute carpels also may not be primitive. The majority 

 of carpels appear involute, with the sterile border greatly reduced or 

 absent, and the margins meeting, edge to edge. Though the existence of 

 marginal meristems in carpels is well known, little attention has been 

 given to late stages in ontogeny, where position of the marginal meri- 

 stems should aid in determination of the basic type of closing. Avail- 

 able information indicates that, in at least some taxa, the marginal 

 meristems meet directly — evidence of involute closure. Closure of the 

 carpel, where ontogenetic, results in the formation of a more or less 

 distinct ventral suture. The suture varies greatly in form and distinct- 

 ness with the degree of inrolling and of completeness of histological 

 fusion. The openings may extend the full length of the ovary or be 

 restricted to the median or distal parts; in Platanus, the opening is very 

 short. Closure of the carpel is clearly still in process of establishment in 

 the angiosperms. The closed carpel is not a fixed, universal character in 

 "angiospermy," though it serves well as one of a group of distinguishing 

 characters. 



