APPARATUS FOR THE STUDY OF COMPARATIVE 
TRANSPIRATION 
EDGAR N. TRANSEAU 
(WITH FIVE FIGURES) 
The quantitative study of the ecological factors of the habitat 
naturally leads to a similar investigation of the responses of the 
“‘growth-forms” to these elements of the habitat. Thus the in- 
vestigation of the comparative evaporation of various local habitats 
has led to a complementary study of the comparative rates of 
transpiration of the plants occurring in them. In this latter work 
an effort has been made to obtain graphs of the hourly transpira- 
tion rates under a great variety of conditions of temperature, light, 
and humidity. For comparative purposes these data are being 
collected (1) by the synchronous exposure of several plants, and 
(2) by determining the ratios between the transpiration rate and 
the rate of evaporation from a standard vaporimeter. 
It is evident that for conducting a study of this kind, in which 
data regarding the effects of stimuli and latent periods are essential, 
the determination of the water losses by the method of weighing 
at intervals of several hours is, to say the least, unsatisfactory. 
A very perfect apparatus for the automatic weighing and recording 
of evaporation rates has been described by GANonc in this journal.” 
For comparative purposes, however, several of these instruments 
are required, making the cost beyond the means of at least some 
laboratories. The following apparatus is essentially a modification 
of the Ganong transpirograph, developed for the special purpose 
of comparative work. Its efficiency, combined with its compara- 
tively small cost, has made it seem worth describing in advance 
of the discussion of the data which are being obtained by its use. 
The complete outfit, as shown in fig. 1, consists of a hygro- 
thermograph, a chronograph, chemical balances, weight droppers, 
* New precision appliances for use in plant physiology. Bor. GazETTE 39:145. 
1905. 
Botanical Gazette, vol. 52] [54 
