1912] LIVINGSTON & BROWN—TRANSPIRATION 327 
thus far, was carried out on August 21 and 22. From 5 A.M. on 
the first day till 6 a.m. on the second, hourly weighings were made 
on two potted and sealed plants of Physalis, while corresponding 
readings were obtained from a porous cup atmometer having the 
same exposure. The two plants were similar to each other and, 
though somewhat smaller, not dissimilar to the Physalis plants of 
the leaf moisture tests of the same period (table II), so that the two 
series of data are fairly comparable. Space will not permit the 
presentation here of the transpiration and evaporation rates and 
of the resulting ratios and graphs, but we may mention the findings 
of most present interest. Averaging the data for the two plants 
(these data are very similar), the maximum of absolute transpira- 
tion occurred from 11 A.M. to 12 noon, while the maximum rate of 
loss from the porous cup atmometer fell three hours later. The 
maximum of relative transpiration occurred from 12 noon to I P.M.; 
thus the non-stomatal retardation of water loss became effective 
about 1 p.M. As already shown (table II), the moisture content 
of the leaves of Physalis in the open soil fell during the period from 
9 A.M to 3 P.M., and rose again to its maximum, or what we may 
term its normal, at 7 P.M. From these data we see that the non- 
stomatal retardation of water loss became manifest in the potted 
plants four hours after the leaf moisture had begun to decrease in 
the plants in the open, and two hours before the occurrence of the 
minimum water content. The maximum evaporation rate occurred 
in the hour preceding the minimum water content. All of these 
points are quite in harmony with the requirements of the hypothesis 
of incipient drying, and the data appear to substantiate this 
hypothesis, so far as their incomplete nature will allow. 
The work of Briccs and SHANTz™ on some of the conditions 
which determine wilting has thrown not a little indirect light upon 
the question of the occurrence of incipient drying. By the ingenious 
balanced system which these authors devised, they have shown 
clearly that, with the gradual drying out of the soil, there comes a 
time when the rate of entrance of water into the upper part of a 
plant is surpassed by the transpiration rate. This is, of course, 
* Briccs, L. J., and SHantz, H. L., The wilting pane for different plants and 
its indirect determination. Bur. Pl. Ind. Bull. 230. 
