THE STEM OF PLANTS. 47 
stipa), perceptibly equal in thickness from the base to the summit, 
and completely bare, that 
is, not divided by boughs 
and branches, making 
them like some tall column 
surmounted with a thick 
tuft of leaves. What is 
the interior structure of 
this stipa? To give an 
idea of its formation, we 
must first understand that 
. the growth of the Palm- 
tree differs from that of any 
group of trees we have 
hitherto considered. Palm- 
trees do not, like our ever- 
green and forest trees, in- 
crease their growth by 
concentric layers, deposited ~ 
between the wood and the 
bark. The interior struc- 
ture, therefore, must show 
arrangements very different 
from those we have been 
describing. Here there is 
no single central canal 
destined to hold the pith, 
no concentric layers dis- 
tinctly separating the pith, 
the wood, and the bark; 
no medullary rays diverg- 
ing from the centre to the 
circumference. If we cut 
the stem of a Palm across, 
we shall immediately see 
that it differs as much from 
the trunk of our trees in its 
x 
> 
Fig. 54.—Section of the stem of a Palm, -4 
Q aS aaa ~ * 
D D 
c 
C c 
3B 
B 5 
A 
A A 
Fig .55.—Theoretic figure showing the internal 
structure of the Palm, 
inmost organisation as it does in its outward appearance. We look 
~ 
