1914] GATES—X EROPHILY 463 
varies directly with the temperature, inversely with the relative 
umidity, and is greater in daylight than in darkness. The last 
may be almost entirely included in the two former, as the absorp- 
tion of radiant energy during the day would increase the tempera- 
ture of the leaf were it not 
used up in augmenting tran- wou 18 12 3 is 18 16 17 108 29 
spiration. For example, on oc. \ 
February 27-29, with a | +16 e/nr/100 on® \e teepsraton 
temperature constant to | -15 5 
within 2° and the relative |.14 oo \ 
humidity constant to within |.,5; calyculata’ 
5 per cent, in plants of | .,5 Room conditions 
Chamaedaphne which were 
-11 Radiator condi- 
run in the laboratory with Sone san=- 
light about 0.1 per cent of € \ 
sunlight, not at any time ie : 1° Be 
being exposed to direct sun- | °°? “7” Se = ne 
light, the rate of transpira- |-°7 °* " 2° Bee ele Mn, 
tion was very noticeably |-0¢ 
higher (0.071 gm. and |.os ~ oe GO 
0.083 gm.) during the | se.” See 
diffuse daylight than in the | he 
periods of darkness before “ es 
and after. During the 
night following, with the 
temperature constant but 
the humidi ty dropping o Relation of Solution insta 
= ° ° to Transpiration in Ohamaed 
slightly, the transpiration of 
these same duplicates de- Fic. 5.—The relation of solution tempera- 
creased to 0.0 46 gm. and ai to Bs 8 in Chamaedaphne calycu- 
0.060 gm. respectively. — 
Only rarely does the rate of transpiration exceed 0.01 gm./hr./ 
100 sq. cm. in any of the plants experimented with under winter 
conditions. With the exception of Vaccinium macrocarpon, the 
tate was more often less than 0.005 gm. than above it. In 
the deciduous shrubs it was usually below o.0co1 gm., and not 
infrequently was hardly within the power of measurement with 
