
96 A TEXTBOOK OF GENERAL BOTANY 
The stem is frequently an important storage organ. During 
a large part of their lives many plants manufacture food faster 
than it is used; in most cases a large part of this surplus is 
stored in the stem. A stem is a better storage organ than an 
ordinary leaf, as it is usually a more permanent structure. More- 
over, it is of advantage to the plant that the surplus food 
manufactured in the leaves is removed from them, so that food 
material does not accumulate and interfere with its continued 
production. 
STRUCTURE OF STEMS 
Nodes and internodes. The stem (Fig. 91) is composed of nodes 
(the places where leaves and branches originate) and internodes 
(the parts of the stem between the nodes). Branches usually 
originate at the 
= = SS) <i) nodes in the axils 
hy SS of the leaves, that 
: yy) 2 Sy Se is, Just above the 
ea ER 3 point of attach- 
Z; GB (A ment of the leaves. 
| Apical growth. 
‘) The growth in 
A\ length of a stem 
Fig. 91. Horizontal branch of guava (Psidium takes place largely ’ 
guajava). (x 4) and in most cases 
only, at and near 
the tip. Very good evidence of this fact is afforded by an exam- 
ination of an actively growing stem of a dicotyledonous plant 
(Fig. 91). It will be seen that all the leaves, except those near 
the tip, are of about the same size, and that the internodes are 
of approximately equal length. The similarity in size of the 
leaves shows that no new leaves are formed on the older parts 
of the stem, while the similarity in length of the internodes 
proves that when an internode has reached a certain length, 
elongation ceases. If all parts of the stem were to continue to 
grow in length throughout their existence, the internodes would 

