112 



PLANT LIFE. 



outer one, so as to isolate a mass of tissues of greater or less 

 size. When this mass is killed by the formation of a sheet 

 of cork on its inner face it gradually dries up and ultimately 

 breaks away in the form of a scale or flake (fig. 129). Bark 

 of this sort, such as that of the hickory, sycamore, or apple, 



FIG. 129. Part of a transverse section of the bark of cinchona, c, layers of cork 

 formed by a transient cork cambium, s, thin-walled tissues, with occasional stone 

 cells. The sheets of cork cells are lines of weakness along which the flakes of bark 

 split off. Magnified 665 diam. After Warnecke. 



is known as scaly bark. In other trees the dead outer por- 

 tions are persistent, and are only gradually worn away by 

 the action of the weather. Such persistent parts become 

 seamed or deeply furrowed lengthwise by the increased size 

 of the stem within and the constant drying and shrinking 

 of the dead parts. Such bark is called furrowed or ridgy 

 bark. 



