BOTANICAL GAZETTE 
NOVEMBER, 1895. 
Recording apparatus for the study of transpiration of 
plants.! 
ALBERT F. WOODS. 
WITH PLATE XXX. 
Of the various methods devised for determining the amount 
of water evaporated by plants, none is so satisfactory as the 
direct one of weighing the plant at given periods. Weigh- 
ings, however, as ordinarily carried on, are more or less un- 
Satisfactory, for unless the operation is repeated at short in- 
tervals, a broken record is the result. To obviate this diffi- 
culty, various devices have been used. Some of these weigh 
the loss from the plant direct, while others operate by the in- 
direct method of weighing the water absorbed by calcium 
chloride, sulphuric acid, etc. Of the last mentioned class the 
nderson registering balance? is an admirable device which 
with some slight modifications might be made to record di- 
rectly loss in weight. At the suggestion of Mr. B. T. Gal- 
loway, the writer has recently made some changes in Mar- 
vin’s recording rain and snow gauge which fits it for very sat- 
Isfactory work in measuring continuously the loss of water 
from transpiring plants. Prof. Marvin, of the United States 
Weather Bureau, very kindly assisted us in making the 
Changes. The apparatus consists essentially of two parts, a 
balance and a register. (PLATE XXX.) The two parts are 
in an electrical circuit which is opened or closed whenever 
the equilibrium of the balance is disturbed. When the cir- 
Cuit is closed, the movement of the armature of the magnet 
wheel which turns a long screw set parallel to the beam. 
This screw works ina half nut attached to the carriage of the 
2 Read before section G, A. A. A. S. : Springfield meeting, August, 1895. 
*Bull. Geol. and Nat. Hist. Surv. Minn. 9: 117-180. 27 S.1894. 
33—Vol. XX.—No. 11. 
