PRESSURE OF BIRCH SAP. 253 



amounting to 61. OG feet of water. The root was dug up iu 

 October and found apparently alive and healthy. 



The black birch root last year exerted the astonishing pres- 

 sure of 84.77 feet of water, but was not observed through the 

 season. This year, on the eighth of April, a guage was 

 adjusted to a root of the same tree, and, although the pressure 

 was not quite as great as last season, the extreme variation 

 was 102.68 feet. The first pressure was, April twenty-third, 

 and the highest, May tenth, and equalled 77.06 feet, while the 

 greatest suction was on September fourteenth, and amounted 

 to -25.62 feet of water. 



The pressure is evidently caused in these roots, which are 

 entirely detached from the tree and lie in the earth just as 

 they grew, by the activity of their power of absorption, which 

 seems to be greatest just as the buds are about bursting. The 

 suction is remarkably powerful, and must apparently result 

 from some chemical change occurring in the root, after the root- 

 fibres have lost their absorbing power. A critical examination 

 by the chemist and the microscopist would probably give an 

 explanation for this phenomenon. 



The paper birch tree reached its maximum, May sixth, when 

 the pressure was equal to sustaining a column of water 61.20 

 feet in height. The suction on June fourteenth was — 7.Q3 

 feet, and the extreme variation for the season was 69.13 feet. 



On the eighth of April, a gauge was attached to a yellow 

 birch tree near the ground, and, on the twenty-fourth, at 

 noon, the pressure was 73.67 feet of water. A hole was then 

 bored into the tree at a height of thirty feet above the lower 

 one, for the purpose of putting up another gauge. The mer- 

 cury in the lower gauge fell at the rate of four inches per 

 minute, till it stood at a point representing 35.13 feet of water. 

 The sap, at the same time, flowed freely from the upper orifice. 

 The usual difference between the gauges thus placed thirty 

 feet apart Avas from twenty-four to thirty-five feet of water, 

 showing evidently that the power furnishing the pressure was 

 from below, that is, from the root. The maximum of the 

 lower gauge was 74.22 feet, April twenty-second, and the 

 minimum was -22.44 feet, May sixteenth, and, hence, the total 

 variation was 96.66 feet. The upper gauge attained a pressure 

 of 41.25 feet, on the ninth of May, and sank to -11.11 feet on 



