APRIL 49 



most perfect pumps can raise water only 

 thirty-four feet in an unbroken column; so 

 this would be of little value in tall trees were 

 it not for the introduction of small bubbles 

 of air into the column of sap. This makes 

 of it an alternation of bubble and sap, 

 bubble and sap. In such a column, known 

 to science as a Jamin chain, water rises to 

 higher levels, though of course in far less 

 quantity than if the stream were unbroken. 

 Meantime the tree is swaying with every 

 breath of wind. With each quiet breeze 

 the branches bend, and at every sweep the 

 little tubes are flattened. This, of course, 

 lessens their capacity, and a part of the sap 

 is forced upward out of them. As the bough 

 returns to its first position, once more the 

 tubes fill from below, only to unload a part 

 of their burden with the next puff of air. 

 So, as the tree sways from side to side under 

 the freshening wind, the quiet stream goes 

 ceaselessly on. When the storm sweeps 

 furiously over the forest not the least of its 

 results must be the renewed vigor of the 

 trees from the hastened flow of sap; much 



