COURSE OF THE BUNDLES IN THE STEM. 125 



for different stems, and depending often on some external con- 

 ditions, the}' do not further elongate ; but those tissues of the 

 internodes by which growth in length has taken place become 

 gradually firmer, and constitute permanent tissue. It sometimes 

 happens that the nodes and internodes of the stem are not plainly 

 distinguishable from each other. This is the case in most palms, 

 where the growth takes place from the terminal bud alone. 



376. Even a cursory examination of the structure of a stem 

 which has thus unfolded from a bud shows that the number and 

 the distribution of the bundles have much to do with the number 

 and the arrangement of the leaves. Comparative investigations * 

 of large orders of vascular plants have shown that the number 

 of the bundles of the stem always bears some relation to that of 

 the leaves at a given portion of the axis, and to the arrange- 

 ment of the leaves. "The more bundles in a given leaf, and 

 the greater the number of leaves in a cycle or whorl, the more 

 numerous will be the bundles in the stem at that level. In 

 monocotyledons with a large crown of leaves these two condi- 

 tions are met with, and in these stems arc found the greatest 

 number of bundles." 2 



377. Course and distribution of the bundles in the stem. In 

 the internodes, the bundles mostly run parallel to the axis, or in 

 curves of very long radius ; at the nodes, they may interlace 

 transversely. If a bundle is followed through its course from 

 below upwards, it will be found to branch at some of the nodes ; 

 the branch of the bundle going directly into the leaf at that 

 point, or else passing upwards through other nodes until it 

 reaches a leaf, the number of nodes traversed varying according 

 to the kind of plant and the region of the stem. 8 More than 

 one branch of the bundle ma}', however, go to a single leaf. 



378. If, now, the course of the bundle be examined from 

 above downwards, it can be seen that each leaf contributes its 

 simple or compound fascicle to the larger bundle with which that 

 from the leaf sooner or later becomes confluent. The fascicle 

 from the leaf can frequently be followed down for several inter- 

 nodes as a separate thread, the so-called foliar trace. If such 

 foliar traces are nearly isolated in their course, a cross-section 

 of the stem will give a ground-plan of the leaf-arrangement. 

 Usually, however, there is much complexity in the distribution 



1 Nageli : Beitrage zur wissensch. Botanik, 1858, and Hanstein : Prings- 

 heim's Jahrb., 1858. 



2 Van Tieghem : Traite de Botanique, 1884, p. 746. 

 8 Van Tieghem : Traite de Botanique, 1884, p. 733. 



