1918] CURRENT LITERATURE — 281 
NOTES POR STUDENTS 
Transpiration studies.—An excellent review of recent investigations on 
transpiration, by KNnicuHT,? includes the principal contributions for the fiv 
years previous to 1916. Conspicuous among the more recent investigations is 
that by BricGs and SHANtTz3 y os comparison of evaporation from various 
types of atmometers and free w surfaces on shallow and deep tanks, with 
transpiration from alfalfa ralisicais sativa). The departure of the hourly 
evaporation rate of the porous cup atmometers from the hourly transpiration 
rate of the alfalfa seems to be due largely (1) to the marked increase in the 
evaporation over transpiration during the night hours; (2) to the more marked 
response of the atmometers to changes in wind velocity; and (3) to the lack 
of proportionate response on the part of the atmometers to changes in solar 
radiation. The departures amount to 90 per cent for the deep tank, 50 per cent 
for the white cylindrical atmometer, 40 per cent for the brown cylinder, the 
white sphere, and the Bellani plate, and 17 per cent for the shallow blackened 
ci 
diameter and 2.5 cm. high, the water was automatically maintained at a depth 
of t cm 
In view of the divergence of the evaporation rates from the two tanks 
employed in these experiments, it becomes evident that Tuomas and Fercvu- 
son‘ have not taken into account all the variables in their effort to obtain a 
law of evaporation from circular surfaces. This was sought primarily for use 
in standardizing atmometers and other instruments for comparison of water 
loss with that from the plant in the process of transpiration. Their conclusion 
that evaporation from a circular water surface is not proportional to its area 
was already familiar to us, and has been emphasized not only in the investiga- 
tion cited but also by Livingston. 
To facilitate critical studies of transpiration, BLACKMAN and KnicuT® 
have devised an apparatus for controlling air movements about plants under 
investigation and have been able to have constant currents up to a speed of 
25m. per minute. Using this apparatus and otherwise securing carefully 
* Knicut, R. C., Recent work on transpiration. New Phytol. 16:127-139. 1917. 
3 Briccs, L. J., and SHantz, H. L., Comparison of the hourly evaporation rate of 
atmometers and free water surfaces with the transpiration rate of Medicago sativa. 
Jour. Agric. Research 9: 277-202. 1917. 
‘Tuomas, Nesta, and Fercuson, nee On the reduction of tianaplcation 
observations. Ann. Botany 31:241-255. 
5 ivcaasies B. E., Atmometry and ‘the porous cup atmometer. Plant World 
18:51-74. 1915 
° Bracxman, V. H., and Knreut, R. C., A method of controlling the rate of air 
movement in transpiration experiments. Ann. Botany 31:217-220. 1917. 
