192 



MORPHOLOGY OF THE ANGIOSPERMS 



have been termed involute. The rolling appears commonly to have 

 brought the edges of the lamina together (Fig. 74B); where the inroU- 

 ing is greater — an uncommon condition — contact is by strips of the 

 abaxial surface. It seems improbable that all the types of involute carpel 

 have been derived from the conduplicate; this derivation would in- 

 volve a change from contact by the adaxial surface only to contact by 

 the abaxial surface — a major change, far more complicated and cir- 

 cuitous than usually found in evolutionary derivation. The vascular 

 anatomy of the carpel supports the view that the involute closure is 

 not a modification of the conduplicate. In primitive carpels, a narrow 



Fig. 75. Semidiagrammatic sketches of cross sections of syncarpous gynoecia show- 

 ing examples of involute closure of carpels. In B, C, D, E, the carpel margins are 

 obvious. A, Enjthraea Ccntaurium; B, Tetraclca coultcri; C, Isayithus hrachiatus; 

 D, Clewdcndron fallax; E, Premna japonica; F, Limnophila heterophylla. (A, after 

 Baum, 1949; B, C, after Stauffer; D, E, after Junell; F, after Hartl. ) 



marginal stiip of the lamina is sterile. In specialization of the carpel, 

 this sterile band is progressively narrowed (Fig. 74A, 2) and, in some 

 taxa, lost (Fig. 75B to £), and the ovules seem to be borne on the 

 margin itself ( Fig. 75A, F ) . Where, in involute carpels, the sterile strip 

 is lost and the edges meet directly, the ventral bundles and the pla- 

 centae are brought close together and often fuse into a common bundle 

 (Fig. 74B) and common placenta. Where the sterile margin is nar- 

 rowed but persists, contact is by the abaxial surface, and the sterile 

 band projects inward as two flaring edges (Fig. 74C, 1); contact is in 

 the region of the vascular bundles. Where the inrolling is greater, con- 

 tact is farther back on the abaxial surface, and the ventral bundles and 

 placentae are well inside the locule (Fig. 74C, 2). Extreme inrolling is 

 present in the Labiatae, where the inrolled borders may reach the mid- 

 vein and sometimes become fused with tissues of that region. 



