COURSE OF TRACHEAE TUBES THROUGH STEM 



lOS 



The vascular bundles in most monocotyledonous stems are 

 all leaf traces. It will be 

 remembered that the leaves 

 of these plants are parallel- 

 veined, and usually many 

 bundles descend from a 

 single leaf into the stem. 

 These at first penetrate 

 rather sharply toward the 

 center, and then descend- 

 ing turn gradually outward 

 and unite with bundles 

 from other leaves. The 

 larger bundles go farther 

 toward the" center than the 

 weaker; and so it happens 

 that the bundles in most 

 Monocotyledons are not ar- 

 ranged in a concentric circle 

 as in Dicotyledons, but are 

 more or less promiscuously 

 distributed, as seen in the 

 stem cross section (Fig. 49) . 

 Monocotyledons with 

 hollow stems vary from 

 this plan in that the bun- 

 dles keep closer to the per- 

 iphery; and in the grass 

 type of stem the bundles 

 are united at the nodes by 

 a plexus of anastomosing 

 branches. 



Throughout all classes of 



stems it is a noteworthy ^^^ so._Diagram showing the course of the 



fact that the leaf has one vascular bundles in a stem of Clematis viticella. 



J. Median bundles from the leaves are marked A, 



or more vascular bundles lateral bundles S and C. (After Nageli.) 



