A Recording Transpirometer. 
BY 
V. H. BLACKMAN, Sc.D., F.R.S. 
AND 
S. G. PAINE, B.Sc., F.I.C. 
With two Figures in the Text. 
'I instrument which will automatically record the amount of water lost 
l \ by a transpiring plant is of great service in many physiological and 
ecological studies. Of such instruments the most practicable type is that in 
which the loss in weight is automatically registered by means of a balance 
provided with some special mechanism. A number of such instruments 
have been devised, mainly by workers in the United States, but either they 
have never been put upon the market or else their cost is very high. 
The first accurate recording balance which could be satisfactorily used 
for measuring the transpiration of a potted plant appears to be that described 
by Anderson , 1 who was the first to use the method of balancing the scale- 
pans by means of metal balls released at intervals by an electrical device. 
This balance seems never to have been put upon the market, and obviously 
would be costly to reproduce. 
Woods 2 has invented another type of transpirometer on the plan of 
a recording hygrometer, which does not seem to have come into use. The 
best-known type of recording instrument is that of Ganong , 3 which of late 
years has been somewhat modified, and is described in his book on Plant 
Physiology. In this instrument, which is very ingenious and convenient, 
the scale-pans, as in Anderson’s balance, are kept in equilibrium by steel 
balls which are added when required. It has, however, two drawbacks : 
it is expensive, thus prohibiting the use of a number of instruments in com- 
parative work, and it is adapted to one particular weight only, the steel 
balls weighing one gramme. The instrument thus only records the time- 
intervals required for the loss of one gramme of water ; an interval which is 
1 Alex. P. Anderson : On a new Registering Balance. Minnesota Botanical Studies, Bull. 9, 
Pt. IV, 1894, p. 177. 
2 Bot. Gaz., xx, 1893, p. 473. 3 Bot. Gaz., xxxix, 1905, p. 141. 
[Annals of Botany, Vol. XXVIII. No. CIX. January, 1914. 
