49 A TEXT-BOOK OF BOTANY 
Branches as well as leaves appear at the nodes; and there is 
usually a very definite relation between them, the branch 
appearing in the up- 
per angle between leaf 
and stem, called the 
azil of the leaf (Fig. 
41). Most branches 
are thus axillary in 
position. The inter- 
nodes give length to 
‘ the stem, separating 
[ the nodes from each 
other, and so display- 
Fic. 41.—A scarlet runner bean, showing leaf- ing the leaves more 
aces internodes, and axillary freely to the air and 
the sunlight. 
23. Direction of stems.—The direttions in which stems 
grow are due to a variety of causes, some of which will be 
considered later; but for the present only certain positions 
will_ be noted. 
(1) Erect stems.—The upright stem is the most common; 
and it seems altogether the best adapted for the proper 
display of leaves, for they can be spread out on all sides 
and carried upward toward the light. To maintain the 
erect position is not a simple mechanical problem, and in 
large woody stems it involves an extensive development 
and arrangement of supporting tissucs. That some special 
organization is necessary to maintain the erect position in 
the air is evident when aerial erect stems are contrasted 
with submerged erect stems. In small lakes and slow- 
moving streams submerged plants ure commonly seen, as 
the pickerel-weed and numerous others. In the water 
the stems are erect; but when taken out they collapse, 
having been sustained in position by the water. 
Among aerial stems the tree is the most impressive, and 
