SEED-BEARING PLANTS . 415 



mutual shading and crowding, resulting in natural 

 pruning, when trees grow close together in the forest. 



367. Long and Short Branches. The pines, like several 

 other groups of plants, bear two distinct kinds of branches 

 long branches, and short branches. The short branches 

 are often called "spur-shoots." Long branches, in 

 addition to being longer and larger, commonly bear 

 only scale-like leaves, while the spur-shoots bear the 

 foliage-leaves (Fig. 308). In certain cases juvenile forms 

 of long branches are recognized, which bear foliage-leaves 

 as an exception to the general rule. 



368. Leaves. The long, needle-like leaves of the pine 

 are familiar to everyone. They occur on the spur-shoots 

 in groups or fascicles of one, two, three, or five, according 

 to the species. The spur-shoots are borne in the axils of 

 the scale-like leaves of the long shoots (Fig. 307). The 

 base of the leaf cluster is sheathed by the thin membranous 

 scales of the terminal bud of the spur. When there are two 

 leaves in a fascicle they are semi-circular in cross-section, 

 the adjacent faces being flattened as a result of their 

 contact in the bud; when there are three or more they 

 are triangular in cross-section. The white pine (Pinus 

 Strobus), and its nearest relatives, have five leaves to a 

 fascicle, the pitch-pine (P. rigida), and its nearest relatives, 

 bear the leaves in threes, the scrub-pines and the Euro- 

 pean pine (P. sylvestris), in twos. 



369. Leaf -fall. The duration of the leaves varies with 

 the species and the locality from two to ten years. As a 

 result there are always green leaves on the tree, whence the 

 term "evergreen." That the leaves are shed may be 

 easily determined by examining the ground under any 

 pine tree. The duration of the leaves is also easily 



