Cork and Bark 



151 



with brittle corks which come to pieces when we 

 try to pull them out of bottles. They crumble 

 because they are full of dark-brown stripes of 

 powdery substance. These stripes were the 

 " lenticels " of the cork tree. 



On the trunks of the birches, especially on the 

 A B oldest parts which 



are nearest to the 

 ground, there are 

 rough black stripes 

 running part way 

 around the tree. 

 These are old len- 

 ticels. 



On the smaller 

 branches of the 

 birch, alder, and 

 wild cherry there 

 are little humps, 

 much lighter in 

 color than the sur- 

 rounding bark. 

 These are young 

 lenticels — and there is much to be said concern- 

 ing lenticels, both old and young (Fig. 37). 



All trees have them on twigs, branches, and 

 trunks, but sometimes they are sunk in the pits and 

 channels of rough bark and very difficult to find. 

 On smooth-barked trees they are much more easily 

 seen, and they appear plainly on peeled-off sheets 



Fig. 37. A, Branches of alder; B, and 

 of poplar-leaved birch; C, showing lenticels. 

 (From a drawing by J. G. Porter.) 



