PRESSURE OF GRAPE SAP. 255 



vine which was tapped began to flow, though it was half a 

 mile distant. The pressure on the gauge steadily diminished 

 through the season, and, on the fourteenth of September, 

 amounted to 19.35 feet. The extreme variation was 93.27 

 feet of water, and, therefore, 9.41 feet less than in the case 

 of the black birch root, which exhibited a much greater suc- 

 tion, though less pressure, than the grape root. 



The other vine selected for trial was nearly four inches in 

 diameter and more than fifty feet high. To a large branch 

 of this, near the ground, was attached a gauge by means of 

 a rubber hose, the branch being cut off for that purpose. A 

 second gauge was secured to another branch at the height of 

 thirty feet above the first, and observations made upon them, 

 once, twice, or three times, daily, from May seventh till June 

 thirtieth. After this, occasional visits were made to the vine, 

 though the variations were very slight. The pressure on the 

 lower gauge began on the seventh of May, when it was 11.11 

 feet of water, and reached its maximum on the twenty-sixth 

 of the month, equalling a column of water 83.87 feet in height. 

 The pressure declined quite rapidly as soon as the buds be- 

 gan to develop, and fell to zero, June thirteenth. The greatest 

 suction was exhibited on the twenty-ninth of June, and was 

 equal to sustaining a column of water 14.39 feet high. Dur- 

 ing the month of July, when growth was most rapid, the suc- 

 tion was uniformly about -7.37 feet of water, and, during 

 August, about -4 feet. The extreme variation on this gauoe 

 amounted to 98.26 feet, though the pressure was somew r hat 

 less than was shown by that on the detached root of the vine 

 already mentioned. 



The upper gauge was not reached by the sap rising from 

 the root until some days after pressure was manifest at the 

 lower one. On the twelfth of May, the lower one stood at 

 34.11 feet of water, and the upper at 3.40 feet. The max- 

 imum pressure was attained, May sixteenth, and was 39.6(5 feet, 

 while the greatest suction occurred, June twentieth, and was 

 -10.77 feet. The extreme variation of the upper gauge was 

 50.43 feet. The difference between the two gauges was usu- 

 ally from 20 to 30 feet of -water ; but when the pressure on the 

 lower one was greatest, the difference was 60.41 feet, in con- 

 sequence of the fact that the force was entirely from the root, 



