344 BOTANICAL GAZETTE [NOVEMBER 
one end of which a leaf or shoot was sealed, while the other 
was connected with an areometer. The water absorbed by the 
shoot was drawn from the areometer, which would then rise, and 
its rise could be recorded by a needle attached to it and traveling 
on a smoked cylinder. As far as I know, this apparatus has_ 
never been used at all. Pfeffer’s citation of Marey is ‘‘ Methode 
Graphique, 1st ed.,” which I have not seen. In the second edi- 
tion, 1885, pp. 255-258, are brief descriptions of several machines 
for the automatic registration of changes in weight, used in - 
meteorology to measure rainfall, but equally adapted to use in 
measuring transpiration, as is illustrated by a curve obtained by 
Marié-Davy with one of them. Anderson’s’ plan is to collect 
the transpired water by means of an absorbent on a scale pan. 
When the balance is sufficiently disturbed, an electric circuit is 
closed, which drops a weight on the other pan, restores the 
equilibrium, and makes a record of the time. 
Woods® has used a rain gauge to measure transpiration, the 
machine being set up so that the plant’s loss of weight opens an 
electric circuit, this moves the tracing pen and also a counter- 
weight, which closes the circuit again. A sample of the record 
shows the soundness of the device. Francis Darwin’? speaks of 
an attempt to construct a self-registering balance by placing 4 
spring under one pan and prolonging the knife edge as a tracer. 
All of these devices except Darwin’s, which was never applied 
to measuring transpiration, are founded on one or the other of 
two principles: the use of the areometer, as in the apparatus of 
Rédier and of Salleron, cited by Marey, and of Eder, Krutizky, 
and Vesque; or the imposition of counterweights at the instant 
demanded by the change in weight of the subject, as in the 
apparatus of Ragona, described by Marey, and of Anderson and 
Woods. They have employed both of the reliable methods of 
measuring the transpiration, namely, weighing the plant, and 
collecting and weighing the evaporated water. Eder made a 
5 Minnesota Botanical Studies 1: 177. 1894. 
® Recording apparatus for the study of the transpiration of plants. Bot. GAZ. 
473. 
7 Annals of Bot. 7 : 461. 
