THE HERBACEOUS DICOTYLEDONS 



391 



lie on either side of the trace. The leaf trace thus illustrates in 

 the genus Vitis the conservative character which has been asserted 

 for it on earlier pages. The most interesting feature presented 

 by Fig. 2joa is, however, the fact that the leaf trace is subtended 

 externally by a broad mass of parenchyma which on its flanks 

 passes inwardly into the broad rays, separating the foliar segment 

 from its neighbors on either hand. The situation in a general 



FIG. 268. a, transverse section of leaf ray in Leea; b, vertical section of leaf ray 

 in Leea. 



way, in fact, duplicates that found in the case of Leea, except that 

 primitive rays are confined to the traces proper in Vitis and the 

 broad ray subtending the trace is very much shortened in its 

 radial dimension. Fig. 2706 shows the same trace in a lower 

 section or, in other words, considerably below the node. Here 

 the broad ray facing or confronting the leaf trace has disappeared, 

 having been gradually replaced by typical woody tissues, con- 

 sisting of septate fibers and vessels. As a consequence of this 

 situation the flanking rays are now separately continuous to the 

 outside of the cylinder and are not united by a broad tangential 



