25 



In some situations it may be advisable to mix with the maple a num- 

 ber of quick-growing trees valuable for posts or farm lumber, in order 

 to secure early returns on the investment. The best species to use in 

 this way can be determined only for definite localities. Advice in such 

 cases will be willingly furnished by the Forest Service. 



MAPLE SAP. 



The quantity of sap produced depends not only upon the size of the 

 tree, but also on its relative situation, and often upon what seem to be 

 peculiarities of the individual tree, not yet explained. ' 



SAP PRESSURE AND FLOW. 



It has been recently shown that the force exerted by the sap of 

 maple trees in the sugar-making season varies from a suction of 2 

 pounds per square inch at night to a pressure of 20 pounds per square 

 inch in the day, and that it fluctuates in a general way with the rise 

 and fall of temperature during the day and night. a Although the 

 phenomenon of sap flow is not yet perfectly understood, it may be 

 asserted that the popular idea of sap rising in the spring and retreat- 

 ing to the roots of the tree in the autumn is a fallacy. Conclusive 

 experiments have shown that on tapping the tree a flow of sap both 

 from above and below comes toward the holes. There is also a very 

 small flow from the sides of the tap holes, the sap moving freely up 

 and down the grain of the wood, but very slowly and in small quan- 

 tities across it. Since the flow varies with the season, the day, and 

 the variation of temperature between day and night, different quanti- 

 tities of sap are yielded by the same grove and the same trees in 

 different years. These circumstances make an average yield very dif- 

 ficult to estimate. However, it may be said that an ordinary mature 

 and thrifty maple will produce about 12 gallons of sap, or 3 pounds 

 of sugar, per season. This figure is not extreme, for a sugar grove 

 has been known to average 19 gallons of sap per tree during eight 

 consecutive seasons, which included one poor year. Some trees have 

 been credited with enormous yields. For instance, a tree in Ver- 

 mont is known to have produced 30f pounds of cake sugar in one 

 season, its sap being so rich that 7 quarts made 1 pound of sugar. 

 Another maple in the same State gave 175 gallons of sap in one 

 season. 6 



There is no doubt that large-crowned trees yield the most sap, so 

 that those trees grown in the open produce the greatest quantities. 

 A too open grove, however, is not to be recommended, because the 

 yield per acre is necessarily less from the smaller number of trees, and 



a Bui. 103, Vermont Agricultural Experiment Station, 1903. 



& Timothy Wheeler: Proceedings of Vermont Sugar Makers' Association, 1900. 



