62 VERMONT AGRICULTURAL REPORT. 



cause expansion or contraction of the volume of imprisoned gases, and 

 changes in pressure of the imprisoned gases. Increase of water con- 

 tent and rising temperature produce pressure, pressure induces sap 

 movement, and sap movement means sap flow. Alternations of temper- 

 ature above and below freezing, cause alternate conditions of pressure 

 and suction, and bring about a pumplike action which accounts in some 

 measure for the intermittent flow. Pressure comes from above and be- 

 low the tap hole, and but slightly from the side. The sap flow comes, 

 under ordinary conditions, chiefly from tissues directly above and below 

 the tap hole. 



4. What bearing has location of the tree and variations in tapping on 

 the amount and character of the flow? Trees in the open give more 

 and richer sap than those further back in the bush, crowded and shaded, 

 because of greater leaf expansion and sun exposure. No more sugar 

 is yielded by tapping on the "branchy" side of a tree than on that 

 relatively devoid of branches. A difference of but 4 pounds in 1,000 

 was noted in favor of the side which was well filled out. Without ex- 

 ception more sugar was obtained from the outer one inch and a half 

 than from tissues deeper in the trees. 



Four-fifths of the sugar yielded from a tap hole 6 inches deep came 

 from the first or outer 3 inches of wood tissue. The remaining fifth 

 would not compensate for the extra labor of boring and increased in- 

 jury to the tree. 



On typical sap days a tap hole on the south side yielded the most 

 sugar, but on other days, particularly if cloudy, when all sides of the 

 tree warmed more equally, the outcome between taps on different sides 

 of the tree was more uniform. 



No decided advantage arises from a too careful selection of any par- 

 ticular side for tapping. The best results will be secured by selecting 

 a point that does not show the nearby marks of recent tappings. 



The sap obtained from the customary tapping height (4 feet) was 

 found to be greater in quantity and better in quality than that from 

 the root (at ground level) or higher on the tree (14 feet above the 

 ground). 



Twenty-seven percent, of the total sugar yielded came from the 

 root tap, 61 percent, from the main tap and 22 percent, from the high 

 tap hole. The high tap hole ceased running earlier in the day than did 

 the others. 



The larger the tap hole the more sap and sugar for a time at least. 

 It is unwise, however, so to wound the tree that the tap hole will not 

 soon heal over. A ^ to % inch sharp bit is recommended for tapping. 

 The hole should be free from shavings, borings, etc.. before the spout is 

 inserted. 



The spout selected should not obstruct the wood tissues of the tree, 

 should securely hold the pail and should be easily inserted and removed. 

 The bark should largely contribute to the firm holding of the spout. 



5. What is the extent and cause of sap variation? Sixty-three per 

 cent, of the sap drops before noon. There is a slight betterment in its 



