338 



STATE POMOLOGICAL SOCIETY. 



The wood of the detached root absorbed the water from the gauge, so as to 

 exert a suction, like the roots of most other species of trees in early spring, but 

 the pressure exhibited at any time was scarcely worthy of mention. So strange 

 did this appear, that on the fourth of April the gauge was removed to a healthy 

 root, detached from another tree, and to avoid any possibility of error, it was 

 afterward connected with a third root, but the results were always similar. 

 It is certain, therefore, from these observations, as well as those connected with 

 the water-gauge, described on a preceding page, that the rise and flow of maple 

 sap is not directly caused by the activity of absorbent rootlets. 



Secondly, it is seen that the movements of the sap in the heart of a tree are 

 much less rapid and vigorous than those occurring in the sap-wood at the 

 same level. This is doubtless owing to the fact that the old wood is more 

 dense, and therefore less permeable to fluids than the outer layers of alburnum; 

 and also to the circumstance that the variations of temperature, at the depth 

 often inches from the bark, are necessarily slow and limited. 



Finally, it remains to consider the extraordinary fact that the greatest suc- 

 tion, as well as the highest pressure, was exhibited by the gauge in the top of 

 the tree. On the eighteenth of April the lower gauge in the sap-wood indicated 

 a pressure equal to 10.77 feet of water, while, at the same time, the upper 

 gauge showed a pressure of 34.93 feet. On the thirty-first of March, the gauges 

 were all frozen, number one standing at 28.90 feet of water, while number five 

 indicated a suction equal to -26.07, a difference of 54.97 feet. In the case of 

 number one, attached to the trunk near the ground, it seemed that the gauge 

 froze before the body of the tree was much chilled, while, by the sudden freez- 

 ing of the branches, the sap was abstracted from the upper gauge before the 

 cold had penetrated the coverings sufficiently to freeze it. 



On the nineteenth of April the upper gauge showed little or no pressure, 

 while the lower one still indicated a pressure of 17 feet. This was apparently 

 due to the absorption of the sap from the branches by the expanding buds. 



In view of all the phenomena thus far observed, it appears that the flow of 

 sap from the maple and other species, which bleed only after being frozen, is 

 in no sense a vital process, but purely physical. The sap is separated from the 

 cellulose of the Avood by the cold, and, under ordinary conditions, gradually 

 reabsorbed. If, however, the tree be tapped so that the liberated sap can es- 

 cape, then it will do so, flowing, as is readily seen to be the case with the 

 maple, most copiously from above. The bleeding is therefore a sort of leakage 

 from the vessels of the wood, but this is doubtless increased by the elastic 

 force of the gases in the tree, which are compressed by the liberated sap, and 

 this expansive power must be intensified by the increase of temperature whicli 

 always accompanies a flow. 



