114 FIELD, FOREST AND FARM 



It is this sap that, in the spring, when it is in great 

 abundance, forms between the wood and the bark 

 a thin layer of slightly viscous moisture and makes 

 the bark easy to peel from its branch. Which of you 

 in the month of May has not taken advantage of 

 this peculiarity to peel off all in one piece a tube 

 of bark from a very smooth twig of willow or lilac 

 in order to make a whistle, trumpet, or other noisy 

 plaything, the delight of boys of your age? 



"Nothing is easier than to prove the passage of 

 sap from above downward. If you remove from a 

 tree-trunk an annular band of bark, the nourishing 

 liquid oozes and accumulates at the upper edge of 

 the wound, but nothing of the sort takes place at 

 the lower edge. Arrested thus by a break in its 

 path, the sap accumulates above the uncovered ring 

 and causes there an abundant growth of wood and 

 bark, which piles up in the form of a thick circular 

 swelling, while below the ring the trunk preserves its 

 former size. 



"A tight ligature, by compressing and obstruct- 

 ing the passages through which the nutritive fluid 

 has to pass, causes the formation of a similar swell- 

 ing above the line of stoppage. You may have seen 

 a sapling, bound too tightly to the stake intended 

 for its support, strangled by its own growth if the 

 gardener has forgotten to loose the band in time. 

 Little by little the trunk swells above this band, 

 which is finally overgrown by the bark and even hid- 

 den within its substance. Indeed, it is not rare to 

 find a tree with its trunk caught fast in a narrow 



