CAUSES OF FLOW. 261 



large tree, sixty feet in height and four feet and a half in 

 girth, was cut early in December, 1874, and firmly lashed in an 

 upright position to neighboring trees. A fire was then kin- 

 dled around the lower end of the trunk, in order to dry and 

 close as far as possible the pores of the wood. Next spring 

 it is proposed to apply mercurial gauges to determine whether 

 the sap moves, as in trees in a natural condition, and after- 

 ward to collect and analyze the sap. 



While it is certain that the flow of the grape and the birch 

 results from the great activity of the absorbing rootlets when 

 they first awake in spring from their winter's repose, it seems 

 equally evident that root absorption has no direct connection 

 with the flow of maple sap. This discovery was made by 

 means of five mercurial gauges, which were attached with 

 great care to a fine, vigorous tree, about sixty feet in height, 

 on the twentieth of last March. The gauges were so con- 

 nected with all parts of the tree that every movement of the 

 sap would be indicated. Number one was joined to a stop- 

 cock inserted into the sap-wood about two feet from the ground, 

 the hole being about one inch in diameter and two inches deep. 

 Number two was connected by a stout rubber hose to a root 

 one inch in diameter, which was laid bare by the use of a 

 force-pump, so as to avoid breaking any of its fibres. This 

 root was cut open at the distance of about two feet from the 

 tree, and gauge number two united to the stump, which was 

 attached to the trunk. Number three was joined in the same 

 way to the large end of the detached root, which remained in 

 the soil just as it grew. Number four was fastened to a piece 

 of gas-pipe one inch in diameter, which was screwed into the 

 tree to the depth of ten inches, a thread having been cut for 

 this purpose on the outside of it. No sap could enter this 

 gauge except at the very centre of the heart-wood of the trunk. 

 Number five was attached to the sap-wood among the branches, 

 at an elevation of twenty feet above gauge number one. The 

 gauges thus connected were then inclosed in tight pine cases, 

 and the metallic pipes and stopcocks wrapped in woolen 

 blankets to protect them from the cold. The observations 

 were taken regularly at six A. M., at noon, and at six r. m., 

 for about ten weeks, until the changes became unimportant. 

 The table appended gives all the variations of sap pressure 



