OBSERVATIONS UPON THE PHENOMENA OP PLANT-LIFE. 331 



syphon -tube of thick glass, the two legs of Avhich were eight feet long, and 

 about four inches apart. This was inverted and attached to a support of inch 

 board, on the center of which was fastened a scale divided to tenths of an inch. 

 To one leg of the tube at the top was adjusted a brass stopcock, by means of 

 email rubber hose, and to the stopcock was connected by a brass coupling a 

 piece of thick lead pipe of small bore and convenient length, which was joined 

 by another stopcock to the trunk, root, or branch which was to be tested. The 

 stopcocks were so made, with a tube on the top, that communication could be 

 opened between the free air and either the lead or the glass tubing at pleasure, 

 and, when closed from the air, the passage was open between the mercury in 

 the syphon-tube, the water in the lead pipe and the sap in the tree. The ob- 

 ject of this three-way cock was to facilitate filling the tubes with water and 

 mercury, and allowing the escape of any gas which might find its way into the 

 apparatus from the tree. A sufficient quantity of mercury was poured into the 

 inverted syphon to fill the two legs to the height of about forty inches, and 

 the remainder of the leg connected with the tree, as well as the lead pipe, was 

 carefully filled with water, all air being excluded. The other leg of the syphon- 

 tube was left open to the atmosphere. When the sap exerted a pressure, it was 

 indicated by a depression of the mercury in the closed leg of the glass tube and 

 a rise in the open end, the diiference between the two columns showing the 

 pressure in inches of mercury. Suction into the tree was marked by the rise 

 of the mercury in the closed leg and its depression in the open one, and in 

 making the record the minus sign was prefixed to the figures expressing the 

 number of inches of mercury. 



One of the difficulties encountered in these experiments arose from the lia- 

 bility to leakage, either around the stopcock inserted into the tree, or from 

 accidental wounds to the bark or small branches. In cases where the pressure 

 was very great, it was sometimes necessary to solder a heavy sheet of lead to- 

 the stopcock and nail it to the tree with a packing of white lead in oil. Much 

 trouble was also experience^ from the bursting of the lead pipes and the break- 

 ing of the glass tubes during severe cold weather by the formation of ice within 

 the gauges. To avoid this as much as possible, the gauges were enclosed in, 

 wooden cases, and the more exposed portions wrapped in woolen blankets. 



Mercurial gauges were attached to the following species, viz. : sugar maple, 

 red maple, black, yellow, white and paper birches, ironwood, apple and grape ; 

 and all the observations may be found in the appended tables. The general 

 results correspond with those of last year, but are much more complete, espe- 

 cially in regard to the two species which exhibio the most surprising phe- 

 nomena and in which the public feel the deepest interest, namely, the sugar 

 maple and the grape vine. 



PRESSUEE OF SAP. 



As soon as the discovery was made, by means of the water gauge, that the 

 apple would flow from the root, a mercurial gauge was attached to a root an 

 inch in diameter. At first, on the fifteenth of May, there was a slight suction 

 amounting to -1.59 feet of water ; but the pressure soon began, and rose to its- 

 maximum, May thirty-first, when it equalled 15.07 feet of water. Thus, the 

 extreme variation was 16.66 feet. 



The butternut had a range of only 13.03 feet, the minimum, -0.79 foot, 

 occurring on April tenth, and the maximum, 12.24 feet, on April fourteenth.. 



The red maple attained its minimum, -2.83 feet, April sixteenth, and its 



