426 



AMHERST EXPERIMENTS ON SAP-PRESSURE. 



bark had been removed 2 inches wide and 5 long, gave 12 pounds more 

 sap than from the heart, but dried up 11 days sooner. 



Birch sap in our climate yields grape-sugar in small quantities, and 

 the sap of the viue, mucilage or gum. In Northern Europe, a sweet 

 sirup is made from birch sap. Cane-sugar is yielded by the maples, 

 walnuts, and hickories, but trom the first only, in profitable quantities. 

 All of these carbo-hydrates appear to be formed from starch stored up 

 by previous growth in the roots and trunk. 



A tree tapped on the north side yielded daily twice as much as from 

 the south, and flowed two weeks longer.^ The sap flows most freely 

 within 12 feet of the ground, and diminishes rapidly above this point. 

 Sap flows from both ends of a cut root, and both contain sugar. The 

 annual tapping of a maple for many years does not appear to iujure it 

 perceptibly in growth. 



The annual average yield of maples is about 60 pounds of sap or 

 2 pounds of sugar.=* Two spouts will yield more than one, but not 

 twice as much, and by still further increasing the number a greater 

 quantity is obtained, but in diminishing degree. 



At certain hours, and on some entire days, the pressure on the gauges 

 showed suction, or absorption, and whenever the sap flowed they indi- 

 cated an outward pressure. The range and flow were much greater on 

 the birch,than on the maple. These results can best be shown by the 

 following tables: 



I. — Flow of sap from certain trees, as observed in the spring of 1874, at Amherst, Mass. 



Trees, &c. 



Acer Pennsylvanicum , 



Acer saccharinum 



Betula alba, var. populifolia 



Betula lutea (1) 



Hetulaluiea (2) 



Betula papyracea 



Oarpinus Americana , 



Juglans cinerea 



Ostrya Virginica 



Titis cestivalis 



C3 O 



H 



16.31 



55. 69 

 174. 38 

 397. 00 

 929. 50 

 , 485. 37 

 6.81 

 18.81 

 286. 06 

 14.56 



In the above observations the Acers and Juglans were notably early, 

 and the Ostrya, Carpinus, and Yitis, late, in flowing, while the Betulas 

 bad a somewhat uniform flow through the season. 



^We arc unwilling to accept this as a rule, and are inclined to regard it as an excep- 

 tion. Very much depends upon whether the epout is inserted over or into a strong 

 vigorous root, and whether upon a side where the roots have a full supply of water or 

 grow in a dry soil. The leaning side of a tree is generally regarded as best for tap- 

 ping, but we are not aware that it has been proved by ex])erimeuts, 



^ .\ tree is mentioned in Leverett, Mass., that yielded 1,400 pounds of sap, or abont 

 14 pounds of sugar in a season. The yield varies considerably one year with another, 

 and iu some soils and aspects more can be made than in others. 



