STEMS 59 
The characteristic sugar has been obtained by the sap from 
food stored in the stem, notably in the older wood. 
26. Growth in length.—Growth in length begins at the 
tip of the stem by the formation of new cells, which are 
organized into alternating nodes and 
internodes. When these regions are 
first formed the internodes are very 
short, and their subsequent elonga- 
tion, separating the nodes, is the chief 
cause of the lengthening of the stem. \@p 
Internodes are able to elongate for © 
only a certain time, so that the elon- 
gating portion of a stem does not often 
extend more than ten to twenty inches 
below the tip. Seedlings such as those 
of the bean should be cultivated, and 
the region of growth, the region of 
greatest growth, and the rate of growth 
determined. The same method may 
be used as was used with the leaf 
(§ 16), in this case each internode 
being marked with equally spaced lines 
in India ink. Measuring these spaces 
at intervals of one or two days will yo. 57,—Scarlet runner 
determine the facts referred to above bean marked with a 
scale of five millimeter 
(Fig. 57). intervals and photo- 
x graphed after forty- 
27. Special forms of stems.—Usu- — Giont hours: the lines 
ally branches resemble the stem from closest together show 
which they arise, but occasionally they dh casinos 
differ in a striking way. That these different structures are 
really branches is usually evident to external observation 
from the fact that they stand in the position of branches, 
that is, in the axils of leaves (§ 22). The three following 
forms illustrate axillary structures that do not resemble 
ordinary branches. 
