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, 

 Avhen, 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 vitas, 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 



