ABSORPTION A VITAL FORCE. 189 



pound of sap having escaped, it was found that both gauges 

 had fallen equal to 19.27 feet of water. Upon closing the 

 hole the gauges rose in ten minutes to their previous level, 

 showing that the rootlets had re-absorbed in that brief period 

 the sap which had escaped from the tree, notwithstanding the 

 enormous pressure already existing. 



A stop-cock having been inserted into the hole opposite the 

 lower gauge, it was found that the communication between it 

 and both the gauges was almost instantaneous, which shows 

 that the tree must have been entirely filled with sap to the 

 height indicated by the column of mercury in the lower gauge, 

 which exerted its pressure in all directions as freely as if stand- 

 ing in a cylindrical vessel as large as the bark of the trunk. 



The sap pressure continued to increase until, on the 4th of 

 May, it represented a column of water 84.77 feet in height, 

 which is believed to be the highest pressure of vegetable sap 

 ever before recorded. 



The buds of the bircK now began to expand, the pressure 

 of the sap to diminish and the oscillations of the mercury to 

 become more decided and regular than before. The upper 

 gauge ceased to vary May 14th, remaining stationary at zero. 

 The lower one declined slowly and varied greatly, but did not 

 fall below zero until May 18th. On May 27th, it also became 

 stationary at zero. The suction manifested by the birch was 

 very little, never exceeding nine feet of water, and continued 

 only for a few days. 



To determine if possible whether any other force than the 

 vital action of the roots was necessary to produce the extraor- 

 dinary phenomena described, a gauge was attached to the 

 root of a black birch-tree as follows. The tree stood in moist 

 ground at the foot of the south slope of a ravine, in such a 

 situation that the earth around it was shaded by the over- 

 hano-ino; bank from the sun. A root was then followed from 

 the trunk to the distance of ten feet, where it was carefully 

 cut off one foot below the surface, and a piece removed from 

 between the cut and the tree. The end of the root, thus 

 entirely detached from the tree, and lying in a horizontal 

 position at the depth of one foot in the cold, damp earth, un- 

 reached by the sunshine, and for the most part unaffected by 



