284 INTRODUCTION TO BOTANY 
needle leaves grow. The needle leaves are really continua- 
tions of these small branches. The inward faces of the leaves 
are so arranged that all of one cluster, when put together, 
compose a cylindrical leaf mass. That is, when two leaves 
compose the cluster, the leaf branch is divided into halves; 
when three or five are in one cluster, the branch is divided 
into three or five parts. 
Gymnosperms are chiefly 
evergreen (that is, keep their 
old leaves until after new 
ones have come), but some 
of them, as the larch, or 
tamarack, and the bald cy- 
press, are deciduous (that 
is, shed’ their old leaves 
before the appearance of 
the new ones). The periods 
during which the leaves 
endure, range in different 
species from two to four 
years. By determining the 
age of the branches through 
Fig. 220. A branch of a pine a study of the yearly bud 
At the left is a one-year-old cone (¢), and at Scars one may readily ascer- 
the tip of the shoot (s) a very young cone tain how long the leaves 
(yc) just open and ready to receive pollen. 
On the young shoot are the young needle last on any pine tree. 
leaves, and at the tip is the bud (b), which The clusters of pine leaves 
continues the growth of the stem i 
are arranged spirally around 
the stem, as may be learned, when they have fallen, by an 
examination of the leaf scars. 
269. Internal structure of needle leaves. The stiffness of 
pine leaves is one of their most noticeable features, and when 
we examine a cross section, we are able to locate the tissues 
that give the leaves their rigidity. The outer layer of cells, 
the epidermis (fig. 221), has an extremely heavy covering, the 
cuticle ; beneath the epidermis there are other heavy-walled 
