GO 



REVIEWS 



How and Why the Sugar Maple Bleeds 



For several years the botanists and chemists of the Vermont 

 Experiment Station, assisted by sundry students of the Univer- 

 sity of Vermont, have been studying certain phenomena associated 

 with maple sap flow. The details of this work are available in a 

 bulletin recently issued.* Some of the more interesting facts 

 and conclusions follow, but only a small portion of these can 

 here be mentioned. 



]\Iaple sap is practically a solution of sugar in water with traces 

 of mineral and flavoring matters. The sugar content averages 

 nearly 3 per cent., but this varies with tree and season. Seasonal 

 variations are related to foliage development and climatic condi- 

 tions. Foliage variations may be considerable. Thus the same 

 tree which carried 8,846 square feet of leaf surface in 1899 

 developed 14,930 feet in 1900. The variations in sap composi- 

 tion between individual trees is even more noteworthy, extremes 

 varying from 1.33 per cent, to 8.20 per cent, being recorded. 

 The trees having larger tops and fuller exposure to light yield 

 richer sap as a rule. There are however large differences where 

 conditions and vigor of the trees appear identical and one must 

 believe that there is individuality in the productiveness of maple 

 trees much as there is in that of milch cows. The average yield 

 per tree in a good season is about three pounds of sugar, which 

 probably represents less than 4 per cent., of the entire sugar 

 content of the tree. 



The time and rate of sap-flow are directly related to .seasonal 

 conditions and temperature variations. Whenever during late 

 winter and early spring sudden fluctuations occur in temperature 

 in the vicinity of 0° C, sap flow begins. Flow develops with 

 ri.sc of temperature above this and ceases with its fall. The.se 

 interrelations between sap movements and temperature variations 

 were closely followed by attaching pressure gages, such as are 

 commonly used on steam boilers, to gas pipes screwed into 

 maple trunks. The flow of sap into such pipes develops pres- 



* Jones, C. H., Eflson, A. \V. and Morse, W. J. The Maple Sap Flow. Vt. 

 Exp. Sta. IJull. No. 103. December, 1903. Obtainable from the Experiment .Station, 

 Burlington, Vt. 



