TISSUES AND SIMPLE ORGANS. 



83 



ocotyledons, SCHWENDENER has designated as cortex that periph- 

 eral portion in which the leaf-traces (the vascular bundles enter- 

 ing from the leaves) in their course downward extend diagonally 

 inw r ard or parallel with the outer surface. As a result the inner 

 boundary of this cortex does not form a smooth, even surface : it 

 is rather a cylindrical surface with numerous projections. 



This leads to the discussion of the arrangement of vascular 



FIG. 48. Arrangement of the vascular bundles in Sedum reflexum. (After Teitz.) 



Each one of the spirally arranged leaves appears with its vascular system, as indicated by the 

 numbers. This figure also has a bearing upon the subsequent discussion of the mechan- 

 ical influence which the position of mature leaf-bundles in the stem has on the position of 

 young leaves. 



bundles in the stem and in other organs. We shall begin with the 

 stem, and allude to the most important facts only. 



Among dicotyledons the leaf-bundles usually extend radially 

 vertical. In most monocotyledons the numerous leaf -traces of each 

 leaf do not all take the same course. The median leaf -bundles ex- 

 tend most deeply into the stem, describing a curve upon the radial 



