Page:The Oak.djvu/137

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119
THE TREE—ITS SHOOT-SYSTEM.
The Oak (Marshall Ward) Fig 30.jpg

Fig. 30.—Transverse section of bark of oak. The successive cork-layers (Perid.) cut out masses of the cortex, and since everything which is thus separated from the underlying tissues dies, scales of bark, consisting of various kinds of tissues—sclerenchyma, d; parenchyma, c; bast-fibers, e; crystal cells, f; etc.—are cut off periodically. All that lies outside the innermost sheet of cork is comprised under the term bark. (Kny.)