76 THE TREE BOOK 



kept from drying out on its upward journey. 

 This little cork suit is a fine, transparent 

 brownish skin, which overlays trunk and 

 branch to the very twig tips. It is made up of 

 cells, ranged row on row, and joined together 

 as accurately as tile flooring. Besides serving 

 to keep, out the heat, the cork layer also acts as 

 a barrier against cold. Each season the tree 

 will add a new cork layer. This is accom- 

 plished by a layer of young ceUs just beneath 

 the cork suit. 



Most trees wear their cork garment beneath 

 their shriveling, weather-istained outer bark, 

 like a union suit. The beeches, birches, sugar 

 maples, and sycamores carry on their cork- 

 making industry lightly and close to the sur- 

 face. These trees have a very thin bark. 

 Other trees, like the oak, the honey locust, and 

 the cork-elm, go into the business on a large 

 scale, making deep plates of cork far beneath 

 the surface. Such trees have a curiously 

 ridged and much-patched bark. For the bark 

 is nothing more nor less than old cork layers, 

 \^hieh have lost their elasticity and been rent 

 and torn and burst asunder as the tree has 

 grown. Some trees, like the pines and larches, 

 make upright, curving cork-plates. These 

 slough off in little irregular shapes, which 



