66 ESSENTIALS OF BOTANY 



its length ; sketch the entire section x 2. Every fibro-vasoular bundle 

 of the stem passes outward through some node in order to connect 

 "with some iibro-vascular bundle of a leaf. This fact being known 

 to the student would Jead him to expect to find the bundles bending 

 out of a vertical position more at the nodes than elsewhere. Can 

 this be seen in the stem examined ? 



Observe the enlargement and thickening at the nodes, and split 

 one of these lengthwise to show the tissue within it. 



Compare with the corn-stem a piece of palmetto and a piece of 

 cat-brier (Smilax rotundifolia, S. hispida, etc.), and notice the simi- 

 larity of structure, except for the fact that the tissue in the palmetto 

 and the cat-brier, which answers to the pith of the corn-stem, is much 

 darker colored and harder than corn-stem pith. Compare also a 

 piece of rattan and of bamboo. 



82. Minute Structure. — Cut a thin cross-section of the corn-stem, 

 examine with a low power of the microscope, and note : 



(a) The rind (not true bark), composed largely of hard, thick- 

 walled dead cells known as sclerenchyma fibers. 



(6) The fibro-vascular bundles. Where are they most abundant ? 

 least abundant ? 



(c) The pith, occupying the intervals between the fibro-vascular 

 bundles. 



Study the bundles in various portions of the section and notice 

 particularly whether some are more porous than others. Explain. 

 Sketch some of the outer and some of the inner ones. 



A more complicated kind of monocotyledonous stem-structure 

 can be studied to advantage in the surgeons' splints cut from yucca^ 

 stems and sold by dealers in surgical supplies. 



83. Mechanical Function of the Manner of Distribution of 



Material in Monocotyledonous Stems The well-known 



strength and lightness of the straw of our smaller grains 

 and of rods of cane or bamboo are due to their form. It 

 can readily be shown by experiment that an iron or 

 steel tube of moderate thickness, like a piece of gas-pipe 

 or of bicycle-tubing, is much stiffer than a solid rod of 



