THE HERBACEOUS DICOTYLEDONS 



395 



magnified image of a part of the transverse aspect of the stem, 

 making clearer the relations of the leaf trace to the large foliar 

 ray. It is apparent that the ray is similar to that found in oaks 

 in cooler climates and that it has a like relation to the leaf trace. 

 In c is shown a diagram of Vitis, illustrating the relations of large 

 rays and foliar traces. The cylinder in this instance shows only 

 a single annual ring, and the rays subtending the leaf trace in 

 transverse section 

 are consequently less 

 deep in the radial 

 direction than those 

 of Leea. Further, 

 in the facial aspect 

 of the cylinder the 

 leaf rays are seen to 

 be much elongated 

 below and separated 

 by a median process 

 of wood into pairs of 

 rays. This situation 

 is strikingly unlike 

 that in the shallow 

 foliar rays of Leea. 

 Still another con- 

 trast to the exotic 

 genus is offered by 



the absence of uniseriate rays except in the actual leaf trace, an 

 interesting exemplification of the persistence of primitive characters 

 in foliar organs. A more highly magnified view (d) of a segment 

 of the transverse aspect of the cylinder makes clear the presence of 

 uniseriate rays in the leaf trace and their absence in the adjoining 

 parts. 



We may now pass conveniently to the diagrammatic comparison 

 of the topographical relations presented by thicker and thinner 

 annual stems of Vitis. In Fig. 2740 is shown a view of a thicker 

 axis from the surface of attachment of a leaf at the median node. 

 The upper part of the figure shows a transverse view of the stem 



FIG. 272. Transverse section of part of a thin axis 

 of Vitis. Explanation in the text. 



