342 THE CONIFERS (GYMNOSPERMS) —FORESTS 
large and thin-walled, strength being sacrificed to size. 
In the fall or during a dry time in summer, the cells formed 
are much smaller and the walls thicker. These small cells 
which show most plainly make up the annual ring. During 
a season in which long, dry periods occur, more than one 
ring may be made. From the center to the bark extend lines 
Figure 316. — Conifers. 
Note the undivided (excurrent) trunk. 
which are made of pith and are known as medullary rays. 
The part of the stem where increase in thickness takes 
place is just under the bark. 
Branches. — The branches leave the stem almost hori¬ 
zontally and nearly in a circle around the trunk of the 
tree. In the pine they curve upward, but each kind of 
evergreen has its own habit of curvature in its branches. 
