ANATOMY OF TISSUES. 97 
length of the stem takes place by the rapid growth and division 
of the very small cells between those points on the stem where 
the lateral organs occur. In this way, the young leaves, while 
still growing outward with their own independent meristem 
tissue, are stretched apart by this intercalary growth of stem. 
The place on the stem where the leaf separates entirely from 
it, fixes the position of what is called a node, that is, the cir- 
cumference of the stem marked by a line drawn around it 
through the base of the leaf, and at right angles to the long 
axis of the stem. That portion of the stem between two nodes 
is called an internode. In some of the monocotyledonous stems 
the base of the leaf extends around this whole circumference 
and the nodes are marked externally by prominent ridges. In 
stems with opposite leaves, the leaves of each pair stand so 
nearly at the same height, that it is convenient practically to 
consider them as standing on opposite sides of the same node, 
the internodes in this case being the separate lengths of stem 
between the pairs of leaves. 
Thus the stem, while constantly being added to, and while 
owing its actual increase in number of cells chiefly to the mer- 
istems at its apex, owes its real extension in length to the sub- 
sequent growth of the new cells so derived. The number of 
cells is also added to during the growth of the internodes by 
cell division, since it is one of the characteristics of lasting 
tissue that it may at any time take on the character of meristem, 
provided only that it still retain its protoplasmic contents. 
The apex of the moss stem and that of nearly all of the vas- 
cular cryptogams consists of a relatively large and actively 
dividing apical cell. From this division results a building 
tissue which usually shows no division into meristems corre- 
sponding to those said to occur near the apex of the phanero- 
gamic stem. When, however, there is an intimation of such a 
division into meristems, both in the mosses and vascular crypto- 
gams, the outer is supposed to correspond to the dermatogen 
