182 BOARD OF AGRICULTURE. 



drawing its sap readily through the other roots of the tree, 

 instead of directly from the earth as before. 



Having observed that a grape-vine which had been cut in 

 the spring was bleeding abundantly, and fearing it would be 

 injured, he attempted to stop the flow by tying a piece of 

 bladder over it. See ng this was forcibly distended, he 

 attached a tube to the stump of the vine to learn how high 

 the sap would rise against the force of gravitation. It soon 

 ran over the top of a tube twenty-five feet high. He then 

 applied mercurial gauges to several different vines, and ob- 

 tained, as the maximum pressure exerted by the rising sap of 

 the grape-vine during the bleeding season, a force sufficient 

 to sustain a column of mercury thirty-eight inches in height, 

 which is equal to a column of water forty -three feet high. 



Nearly all modern books on vegetable physiology, in what- 

 ever language printed, have given the result of Hales' exper- 

 iments as the maximum pressure attained in observations 

 upon the ascent of sap, and the grape-vine has been generally 

 regarded as an exceptional plant in this particular, and thus 

 a kind of stumbling-block in the way^of speculating physiolo- 

 gists. 



To learn how far this might be true, and what were the 

 facts concerning the spring flow of sap in our forest-trees, 

 and especially in the sugar-maple, in re.ard to which scarcely 

 any accurate observations had been made, we began some 

 investigations at the Agricultural College last Maa'ch, the 

 results of which may be summarily stated as follows : 



The great majority of trees and shrubs do not bleed from 

 wounds at any season of ihe year, and the few species in our 

 latitude which exhib t this phenomenon at all do so only 

 when deprived of their foliage. No peculiarity of structure 

 or habitat has ye: been detected to account for this extraor- 

 dinary difierence among them. The soft and spongy wood 

 of the willow or the elm, which often grow in moist ground, 

 might be deemed specially suited to absorb and pour forth 

 water lefore the expansion of their leaves or flowers in 

 spring, but the wood appears to contain scarcely any sap at 

 that time. Of more than sixty species of trees and shrubs, 

 tested by boring a three-quarter inch hole usually to the 

 depth i.f two inc.es into the sap-wood near the earth, only 



