OUR TREES IN WINTER. 45 



formed late in the year become smaller and more densely 

 packed together, forming quite a contrast to the coarser 

 cell structure of summer growth. It is these lines of 

 close-grained wood cells that enable us so easily to count 

 the years of the life of the tree, and their absence in 

 trees grown in tropical countries, that makes it difficult 

 to determine their age. 



As the cold becomes intense, the quantity of water in 

 the cells diminishes. Driven from the cells, it may per- 

 haps be frozen in crystals in some portions of the tree, 

 or even find its way toward the heart wood. In either 

 case, being deprived of the water, the wood contracts, 

 and the tree breaks open as the Lime trees do on Boston 

 Common, the crack being widest of course where the 

 greatest contraction takes place, namely, in the newer sap 

 wood on the outside next the bark. Or in trees having 

 close-grained wood, the trunk may not crack open, but if 

 the tree is cut, frozen chips will show the presence of 

 water. That the old wood of trees contains water in 

 large quantities, and that it may remain in seemingly dry 

 wood for years, every one familiar with an old fashioned 

 open wood fire well knows. 



It is the absence of water in the living cells that ren- 

 ders the twigs of trees so brittle in winter, and the 

 reverse condition which makes them so pliant in summer. 

 We cannot, therefore, say strictly that the sap in plants 

 freezes. Authorities seem agreed upon this, and also that 

 the greater the cold the denser the solid contents of the 

 cells left after the water has been driven out ; hence, their 

 increased ability to withstand the cold. 



The greatest danger to frozen plants arises from the 

 liability of a sudden thaw. If the thaw is gradual, the 

 water is slowly absorbed back again into the cells which 

 gave it up, but if the thaw is very sudden, the cells of 



