384 FOREST PRODUCTS 



when the leaf buds begin to swell. The season, of course, begins earlier 

 in the South than in the North. Professor J. L. Hills, Director of the 

 Vermont Agricultural Experiment Station, has determined in his inves- 

 tigations of sap flow many interesting findings, the chief of which may- 

 be summarized as follows: 



1. The amount of sap flow from a tree under given conditions is 

 directly in proportion to the leaf area and the amount of sunshine it 

 receives. The starch is stored in certain sapwood cells during the 

 preceding summer and through the action of enzymes is transformed 

 from starch into sugar. The alternate freezing and thawing causes 

 expansion and contraction which, with the large amount of moisture 

 drawn up from the roots, excites pressure at the tap hole. Trees in the 

 open with wide, deep crowns, therefore, give much more and richer sap 

 than forest grown specimens with long, straight boles and small shallow 

 crowns. A tree 15 in. in diameter and 50 ft. in height was determined 

 to have 162,000 leaves. This leaf space is equivalent to 14,930 sq. ft. 

 in area representing about one-third of an acre. The weight of the water 

 in the leaves in this tree is estimated to be 242.2 lb. and the total water 

 content of the tree is set at 1220.57 1^. 



2. No more sugar or syrup is obtained by tapping on the branchy 

 or south side of the tree. The compass direction makes no apparent 

 difference in the yield of sap, sugar or syrup. A healthy and fresh por- 

 tion of the bark indicates the best place in which to tap a tree. 



3. Most of the sap flow comes from the first 3 in. of sap wood. Deep 

 tap holes, therefore, are not considered best. Tapping is seldom done 

 now to a depth of more than 2^ in. It was determined that in a tap hole 

 6 in. deep, four-fifths of the sugar came from the first 3 in. Deep tap- 

 ping does not compensate for the extra labor of boring and increased 

 injury to the tree. 



4. The best point at which to tap a tree is about 4 ft. from the ground. 

 This point yields both more sap and better quality sap than lower or 

 higher elevations. An experiment showed that 51 per cent of the total 

 yield of sugar came from a tap 4 ft. from the ground, whereas only 27 

 per cent came from a root tap and only 22 per cent from a higher tap hole. 



5. The best size of tap hole is from f to f of an inch. Seven-eighths 

 of an inch is the size most commonly in use to-day. Generally speaking, 

 the larger the tap hole the more sap and sugar for the time being will be 

 yielded. However, the smaller size holes yield practically as much 

 sap and the hole will rapidly heal over so that the tree is not materially 

 injured. In all cases the tap hole should be cut by a short bit, should 



