I. THE PINES. 51 
from that of other trees, in being made up entirely of woody 
fibres, which are hollow tubes marked externally with rows of 
microscopic, circular disks. 'The resin is deposited in peculiar 
vessels which have received the name of turpentine vessels. 
From the great abundance of resin which it contains, the wood 
is very combustible and remarkable for its durability. In the 
wood of most of the pines the resin does not seem to be depo- 
sited, at least in great quantities, during the life of the part. 
Old trunks are often found consisting almost entirely of heart- 
wood, soft and of a reddish or yellowish color, almost free from 
resin throughout. Where a growing branch is broken off, the 
remaining portion becomes charged with resin, forming what is 
called a pitch-knot, extending sometimes to the heart. The 
same thing takes place, through the whole heart of a tree, 
when, full of juices, its life is suddenly destroyed; and it is com- 
monly supposed that the heart-wood of the trunk of a pitch pine 
increases in weight after it has fallen to the ground. 
The leaves of the pines are very various. Most of the species 
have persistent leaves, and naturally come under the denomi- 
nation of evergreen; but some of them, as the larch and ginkgo 
tree, for example, lose their leaves at the approach of winter. 
In the yew and some others, they are scattered irregularly; in 
some, as the arbor vite, they are opposite; in others, as the 
juniper, they are in whorls; and in the true pines, they are in 
bundles or fascicles, contained in a sheath formed of an altered 
leaf. The bundles in the true pines, and the solitary leaves 
in several of the most nearly allied genera, are arranged in 
spiral lines, which, to the number of five, six, or more, run 
parallel to each other around the tree. The same arrangement 
is found in the scales of the cones. The bundles are considered 
by the botanist as extremely short, abortive branches, as is often 
obvious in the larch. If we examine a pine of the first or second 
season, which may be readily done in our pine forests, we find 
the leaves single. Afterwards, from the axil of the solitary 
leaves, bundles of leaves, or abortive branches make their ap- 
pearance, and finally the leaves are protected at base by a 
sheath. 
The shape of the leaves is singularly various. For the most 
