STRUCTURE OF THE STEM 89 
102. Mechanical Importance of Distribution of Material 
in the Dicotyledonous Stem. —It is easy to see that those 
tissues which are tough, like hard bast, and those which 
are both tough and stiff, ike wood fibers, are arranged in 
a tubular fashion in young dicotyledonous stems as they 
are in some monocotyledonous ones (Fig. 53). Sometimes 
the interior of the stem is quite hollow, as, for example, 
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Fic. 58. — Stem of Box-Elder One Year Old. (Much magnified.) 
A, lengthwise (radial) section ; B, cross-section ; e, epidermis ; ck, cork; 6, hard 
bast ; s, sieve-cells; c, cambium; w, wood-cells; m, medullary rays; d, 
ducts ; p, pith, 
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in the stems of balsams, melons, cucumbers, and squashes, 
and in the flower-stalks of the dandelion. In older stems, 
such as the trunks of trees, the wood forms a pretty nearly 
solid cylinder. 
Stiffness in dicotyledonous stems is secured mainly in 
two ways: (1) by hard bast fibers, (2) by wood fibers. 
Which of these types does the stem (Fig. 55) represent? 
Which does the flax-stem (Fig. 60) represent? 
