SECT. I 



MORPHOLOGY 



135 



side to give place to a newly-entering leaf-trace, with which it 

 finally coalesces at the twelfth internode. The position of a leaf 

 necessarily determines the point of entrance of its leaf- trace 

 into the stem, and accordingly a diagram (Fig. 144) of the bundles of 

 2\ixus will exhibit a divergence of the leaf -traces corresponding to the 

 y'^ divergence of the leaves. The course taken by the leaf-traces in 

 the stem, however, is independent of the leaf position, and varies 

 considerably in different stems, although the divergence of their leaves 



Fig. 144. — Diagram .showing the course of the \ascula!- bundles in a slioot of Tarns haccata. 



may be the same. The stem of Clematis viticella affords an example 

 of leaf traces consisting of three vascular bundles. The leaves are in 

 whorls of two, the successive whorls alternating with one another. 

 The median strand of each leaf-trace (Fig. 145 ad, ak, nq, fx) has a free 

 course through one internode, and at the node below divides into two 

 arms which coalesce with the adjacent lateral strands of the leaves 

 inserted at this node. The two lateral strands of each leaf trace (Fig. 

 145 he, ef, hi, hi, op, rs) also are free throughout the internode, but at the 

 node below curve inwards and become attached to the same lateral 

 strands as the arms of the median bundle of the trace. 



