46 THE STEM. 
the central line, but chiefly occupy the axis. The upper 
parts of the leaves perish, having performed their functions ; 
their bases remain, are pressed together, and form the new 
external part of the stem. In the middle of the crown of 
leaves is the terminal bud, which is next to be developed, 
rise a little above the former, become a cluster of leaves, and 
in its turn be pushed outwards by a succeeding central bud. — 
143. The oldest and hardest part of such stems is that — 
nearest to the circumference. The more the external parts 
are pressed by the descent of the new matter, the more close — 
and compact they become, the outer parts being incapable of 
being much farther pushed out, and the whole being thus 
condensed very much. 
144. From the mode of growth in this stem it never can 
attain a great thickness, the new matter having to foree 
' outwards all the previously formed matter, which is every — 
Season increasing in quantity and becoming harder. They 
often, however, attain a very great height, as is seen in Palms, 
which are occasionally met with nearly 200 feet high. The 
prickly Pole Palm is like whalebone externally ; and some 
palms are so hard there as to resist the stroke of an axe, yet 
quite soft in the centre. 
145. From the same cause they have no lateral buds, no 
branches, Buds, which produce branches, originate from 
the soft and juicy parts of the tree ; but in endogenous trees, 
this is surrounded by a thick, hard, compact casing, through 
which the buds cannot penetrate. In most cases, their only 
branches are the splendid crown of leaves which proceed from 
their one bud at the moment. From their great height, — 
which renders them tottering, and their manner of growth, 
which causes them to become hard and compressed, even in 
the centre, so that they cannot transmit juices from the root, 
or new matter from the leaves, their age is limited, not ex- 
ceeding two or three centuries at the utmost. os 
146. From the absence of concentric layers, each marking 
an year’s growth, it is difficult to determine the age in 
group of plants. An approximate estimate may be 1 
