In Winter Woods 387 



times the cell walls are very thick, sometimes 

 they are thin, and sometimes they are pitted or 

 barred or ringed so that under the microscope 

 they show patterns of great beauty. 



A tiny sliver of wood may be made up of many 

 kinds of cells, which are alike only in one respect 

 that the tree has had a use for them all. 



Toward the centre of the trunk and larger 

 branches lie the oldest cells, whose work is nearly 

 or entirely done. 



They form the " heart-wood " which, as every 

 cabinetmaker knows, is darker in color and closer 

 in texture than the younger " sap-wood " which 

 surrounds it. 



Outside the "sap-wood" there is in spring a 

 layer of young growing cells which are building up 

 new bark and new wood. In April we shall find 

 this forming tissue lying just below the bark, be- 

 tween it and the wood. 



But at this season no active growth is going 

 forward, and no delicate new cells are forming 

 and swelling between the tree and its bark. 



In the bark itself, at varying depths according 

 to the kind of tree, lie several layers of cork-cells. 



In summer this cork undergarment covers all 

 the tree except the tops of its tenderest twigs and 



