STRUCTURE OP THE STEM 



85 



by experiment that an iron or steel tube of moderate thick- 

 ness, like a piece of gas-pipe, or of bicycle-tubing, is much 

 stiffer than a solid rod of the same weight per foot. The 

 oat straw, the stems of bulrushes (Fig. 63), the cane (of 

 our southern canebrakes), and the bamboo are hollow 

 cylinders ; the 

 cornstalk is a 

 solid cylinder, 

 but filled with a 

 very light pith. 

 The flinty outer 

 layer of the 

 stalk, together 

 with the closely 

 packed scleren- 

 ohyma fibers of 

 the outer rind 

 and the frequent 

 fibro-vascular 

 bundles just 

 within this, are 

 arranged in the 

 best way to se- 

 cure stiffness. 

 In a general 

 way, then, we may say that the pith, the bundles, and the 

 sclerenchymatous rind are what they are and where they 

 are to serve important mechanical purposes. But they 

 have other uses fully as important (Fig. 78). 



99. Growth of Monocotyledonous Stems in Thickness. — 

 In most woody monocotyledonous stems, for a reason 



Pig. 64. — Group of Date-Palme. 



