Читать книгу Studies of Trees - Jacob Joshua Levison - Страница 11

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How to tell them from other trees: The spruce and hemlock belong to the evergreen class and may be told from the other trees by their leaves. The characteristic leaves of the spruce are shown in Fig. 9; those of the hemlock in Fig. 10. These are much shorter than the needles of the pines but are longer than the leaves of the red cedar or arbor vitae. They are neither arranged in clusters like those of the larch, nor in feathery layers like those of the cypress. They adhere to the tree throughout the year, while the leaves of the larch and cypress shed in the fall.

The spruces are pyramidal-shaped trees, with tall and tapering trunks, thickly covered with branches, forming a compact crown. They are widely distributed throughout the cold and temperate regions of the northern hemisphere, where they often form thick forests over extended areas.

There are eighteen recognized species of spruce. The Norway spruce has been chosen as a type for this group because it is so commonly planted in the northeastern part of the United States.

The hemlock is represented by seven species, confined to temperate North America, Japan, and Central and Western China.

Fig. 7.—The Norway Spruce.

How to tell them from each other: The needles and branches of the spruce are coarse; those of the hemlock are flat and graceful. The individual leaves of the spruce, Fig. 9, are four-sided and green or blue on the under side, while those of the hemlock, Fig. 10, are flat and are marked by two white lines on the under side.