COURSE OF TRACHEAL TUBES THROUGH STEM 



105 



The vascular ])undlcs 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 tow^ard 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 p^^_ ^o.-DiaRram showing the course of the 



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



, , ,, Median bundles from the leaves are marked A, 



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



