THE HERBACEOUS DICOTYLEDONS 



403 



the sunflower. In this region the foliar traces, instead of being 

 depressed below the level of the woody cylinder, are outstanding, 

 a condition very commonly found in extreme herbs, which have 

 largely lost their woody texture. In the case of the vine the radial 

 diameter of the trace in the slender region of the stem merely 

 equals that of the cylinder, while in strongly herbaceous types 

 the leaf trace is outstanding or salient. In the high part of the 

 sunflower stem the trace is only flanked by storage tissue in contrast 



a 



FIG. 281. a, diagram of lower region of stem of Helianthus hir stilus; b, radial 

 and tangential view of the topographical relations of leaf traces in a; c, diagram of the 

 upper region of the stem in the sunflower; d, topography of the trace in radial and 

 tangential aspects. Full explanation in the text. 



to the both flanking and facing topography of the storage paren- 

 chyma in the lower and more woody part of the axis. It will be 

 noted that in the high portion of the axis the foliar traces cor- 

 respond to elevations or ridges on the surface of the stem, while 

 in the regions lower down they subtend longitudinal furrows. In 

 Fig. 28 id the topography of the foliar trace is represented in 

 radial and tangential aspect. In the upper figure the absence 

 of subtending parenchyma can be clearly discerned, while in the 

 lower one the flanking disposition of the storage tissues is apparent. 



