THE CARPEL 193 



The difRculty of determining whether a carpel of advanced form, 

 with apparently inrolled borders, is involute or conduplicate is in- 

 creased by the trend throughout carpel specialization toward reduction 

 of the sterile borders. In primitive conduplicate carpels, as in Degeneria, 

 these borders are wide; in less primitive types, they are narrower and, 

 in advanced carpels that can still be recognized as conduplicate, they 

 are narrow. In carpels that are probably involute, the sterile borders 

 range from fairly wide to absent, with ovules borne on the very edge. 

 Intermediate stages show vestigial borders. The recognition of these 

 reduced borders as such demonstrates an inrolling that brings together 

 borders of the dorsal surface of the carpel. Evidence supplied by posi- 

 tion of the marginal meristems in carpels of the rolled type is probably 

 not on record and is important for the determination of basic types of 

 carpel closing. 



Where the sterile margins are greatly reduced or lost, the two 

 placentae are brought close together and unite, in greater or less de- 

 gree, in a common placenta. The placenta may show evidence of its 

 double nature in bilobed form. The ventral bundles, which underlie 

 the placentae, may lie side by side or be fused as one simple bundle 

 ( Figs. 74A, 4, 5 and B, 2, 3 ) , regardless of external form of the placenta. 

 A deeply two-lobed placenta with the lobes divaricate and the epidermal 

 layers continuous through the line of union is evidence of fusion by the 

 dorsal surface well back from the edges (Fig. 74C, 2). Orientation of 

 the ventral bundles may be of aid in determining type of folding. In 

 typical conduplicate carpels, these bundles are half inverted; in carpels 

 where edge meets edge or the edges are rolled in, they are typically 

 completely, or nearly completely, inverted. In carpels apparently of 

 involute type, whether in apo- or syncarpous gynoecia, inversion of the 

 ventral bundles is typical. Variations in degree of inversion occur occa- 

 sionally in individual carpels, but this accompanies variations in 

 external form. 



The assumption that all carpel types are derived from the condupli- 

 cate involves complicated changes in orientation of the borders and 

 margins in the phylogenetic development of the more common types. 

 In the conduplicate type, ventral surfaces of the carpel borders are in 

 contact, and the margins lie side by side (Fig. 74A, 1, 2); in the more 

 common types, the margins may come face to face, with no contact of 

 the borders, or the margins, still side by side, are turned inward, and 

 the dorsal surfaces of the borders are in contact (Fig. 74C, 1). Where 

 the inrolling is continued beyond the line of contact, the borders flare 

 and may recurve strongly (Fig. 74C, 2). 



It is difficult to see, in the involute-margin types, modifications of 

 the conduplicate condition, especially in the light of the existence to- 



