“Thus palms are, in gene- 
NUTRITIVE ORGANS OF PLANTS. 115 
outside, but by the formation of new bundles of vessels in the centre, 
which push out those pre- 
viously formed, as long 
as they are soft enough ; 
but when they are tho- 
roughly hardened, this no 
longer takes place, and 
the stem increases in 
length without further Santas 
Seeeonse’ | of. thickness Fig. 75.—Transverse and Vertical Sections of 
7 Endogenous Stem. 

ral, of almost uniform thickness from the root to the crown of leaves, and 
the outer part of the stem is often very hard, whilst the central part is soft 
and spongy, and amongst its cells there is often a great deposit of starch, 
which, in the sago palms, is so abundant as to be of economical import- 
ance. Palms are almost the only endogenous trees, and no endogenous tree is 
found anywhere but in the warmer parts of the globe. Endogenous plants, 
however, abound in all countries, and amongst them are all the grasses 
and all the plants which have bulbs. Endogenous stems are very often 
unbranched, producing no buds but the terminal bud. The great terminal 
-bud of a palm resembles a cabbage in size, and also in aisle. so that 
palms are often cut down for the sake of it. It is called the palm cabbage; 
and some kinds of palm, in which it is particularly good for the table, 
receive the name of cabbage palms. The rapid growth of many endogenous 
stems ruptures the central cells, and thus a hollow stem is produced, 
as In grasses. 
Acrogenous Stems.—Acrogenous stems resemble endogenous stems in 
haying neither pith nor 
‘separable bark, but differ 
from them in their mode 
of growth, all the bundles 
of vessels, or fibres, being 
developed at once, so that 
the stem increases only by 
additions at the summit. 
The acrogenous stem has 
no branches, but produces 
a crown of leaves; so that 
a tree-fern, which is the 
only kind of acrogenous Fig. 76.—Transverse Section Fig. 77. 
tree, has a general resem of Acrogenous Stem. Tree-fern. 
3 3 
blance to a ae In the ferns of Britain and other temperate countries, 
- the stem creeps along the ground as a root-stock. 

. 
