10 RATIONAL FRUIT CULTURE. 



into it some liquid which floats on water, this additional layer 

 will cover the former surface, and will extend further at the 

 edges. If a still lighter liquid is added, we get a fresh cover- 

 ing and a further extension, and so we may go on. But, no 

 matter what additions we make, v/e do not alter the layers 

 underneath, except, perhaps, in a slight degree, by compress- 

 ing them. It is the same with a tree. A ring of new wood 



Fig. 4^Sectlon of a tree-trunk. The arrow polnti to a thin ring of wood termed In a 

 year In which feed wa< scarce. 



is added every year — a thicKi'r rinji in a fat year, when food 

 and water are plentiful, a thinner ring in a lean year, when 

 they are scarce. And those rings remain praclically unaltered 

 during the life of the tree. If it has been starved in any one 

 year either by scanily or liy the absorption of too much of its 



