STRUCTURE OF 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. 55), 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- 
chyma 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 
Ada lle 
hd 
; 
A 
if 
Uidelad 
Fie. 54.— Group of Date-Palms. 
