532 STATE POMOLOGICAL SOCIETY. 



maximum, 18.59 feet, April eighth, the total variation being 21.42 feet of 

 water. 



The ironwood exerted its greatest suction on the nineteenth of May, which 

 •equalled -24.G0 feet, while the greatest pressure was 40.35 feet, and was ob- 

 served May thirteenth. The total variation was thus 64.95 feet of water. 



The white birch began early in the season, April ninth ; reached its mini- 

 mum, -19.26 feet, on the eleventh of May, and its maximum, 39.66 feet, April 

 twenty-third. The extreme variation was, therefore, 58.93 feet of water. 



A gauge was attached to a root of white birch on the eighth of April; the 

 pressure began April twelfth, and steadily advanced to its highest point, 38.08 

 feet. May twelfth, and declined to zero, May twenty-third, and to its minimum, 

 -22.98 feet, August twenty-sixth, the extreme variation amounting to 61.06 

 feet of water. The root was dug up in October and found apparently alive 

 and healthy. 



The black birch root last year exerted the astonishing pressure of 84.77 feet 

 of water, but was not observed through the season. This year, on the eighth 

 of April, a gauge 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 -7.93 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 mercury 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 was 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 the thirteenth of May, the extreme variation 

 being 52.36 feet of water. After the development of the buds, the upper 

 gauge stood uniformly at from -1 to -4 feet of water, and the lower one was 

 mostly minus. 



THE BLEEDING 



of a broken grape vine, in 1723, induced the Kev. Stephen Hales, an ingenious 

 observer of nature, to attach mercurial manometers to the stumps of vine 



