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OBSERVATIONS UPON THE PHENOMENA OF PLANT-LIFE. 337 



wood, and possibly upon the continuance of absorption by the roots to supply 

 the drain upon the tapped tree, it is evident that a large body of snow upon 

 the ground will favor it, since the earth will then be warmer and the night 

 temj)erature of the air much colder than under other circumstances. It does 

 not appear that there is any greater proportion of sap in the maple than in 

 many other trees, but only that for some unknown reason it is separated in 

 greater quantity by freezing, or else not reabsorbed after such separation so 

 quickly as in other species. 



CAUSES OF FLOW. 



For the purpose of learning whether root absorption is necessary to keep up 

 the flow of sap through the season, a large tree, sixty feet in height, and four 

 feet and one-half in girth, was cut early iu December, 1874, and firmly lashed 

 in an upright position to neighboring trees. A fire was then kindled around 

 the lower end of the trunk in order to dry and close as far as possible the 

 pores of the wood. Next spring it is prop )Sod to apply mercurial gauges to 

 determine whether the sap moves, as in trets in a natural condition, and after- 

 wards to collect and analyze the sap. 



While it is certain that the flow of the grape and the birch results from the 

 great activity of the absorbing rootlets when they first awake in spring from 

 their winters repose, it seems equally evident that root absorption has no direct 

 connection with the flow of maple sap. This discovery was mode by means of 

 five mercurial gauges, which were attached with great care to a fine, vigorous 

 tree, about sixty feet in hight, on the twentieth of last March. The gauges 

 were so connected with all parts of the tree that every movement of the sap 

 would be indicated. Xumber one was joined to a stopcock inserted into the 

 sap-wood about two feet from the ground, the hole being about one inch in 

 diameter and two inches deep. Number two was connected by a stout rubber 

 hose to a root one inch in diameter, which was laid bare by the use of a force 

 pump so as to avoid breaking any of its fibres. This root was cnt open at the 

 distance of about two feet from the tree, and gauge number two united to the 

 stump, which was attached to the trunk. Number three was joined iu the 

 same way to the large end of the detached root, which remiiined in the soil 

 just as it grew. Number four was fastened to a piece of gas-pipe one inch in 

 diameter, which was screwed into the tree to the depth of ten inches, a thread 

 having been cut for this purpose on the outside of it. No sap could enter this 

 gauge except at the very center of the heart-wood of the trunk. Number five 

 was attached to the sap-wood among the branches, at an elevation of twenty 

 feet above gauge number one. The gauges thus connected were then enclosed 

 in tight pine cases, and the metallic pipes and stopcocks wrapped in woolen 

 blankets to protect them from the cold. The observations were taken regu- 

 larly at six A. M., at noon, and at six P. M. for about ten weeks, until the 

 changes hecame unimportant. The table appended gives all the variations of 

 sap pressure in different parts of the tree, as recorded at the times specified. 

 A reference to figure 41 will convey a correct idea of the manner in which the 

 mercury fluctuates during every hour of the day and night. 



The following are some of the most interesting results obtained from the 

 several gauges : 

 43 



