I 12 



PLANT LIFE. 



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

 size, ^^'llen this mass is killed by the formation of a sheet 

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

 breaks away in the form of a seale or flake (fig. 129). I'.ark 

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



Fig, 129. — Part of a haiisxxrst; section of tht^ Luik nf cinclmii.i ,, layers of cork 

 formed by a tratisieiit cnrk caniljiuni. s, thin-wallcd tissues, with occasiotial stone 

 cells, 'riie sheets of cork cells are lines of weakness along which the tiakes of bark 

 split off. Magnified 665 diam. — After Warnecke. 



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

 tions are jiersistent, and are only gradually worn a\va\' by 

 the action of the weather. Stieh persistent jiarts become 

 seamed or deeply furrowed lengthwise by the increased size 

 of the stem within and the constant tlrying and shrinking 

 of the dead parts. Such bark is (ailed furrowed or ridgy 

 bark. 



