268 : BOTANICAL GAZETTE [APRIL 
outside the tent at noon is much greater than the difference in 
the average relative humidity of the two stations. 
Evaporation 
Records of the relative rates of evaporation in the two stations 
were obtained by means of the porous cup atmometer described by 
Lrvincston’ and since frequently used in studies dealing with the 
relation between plant functions and meteorological conditions. 
TABLE V 
EVAPORATION FROM POROUS CUP ATMOMETERS 
Date Open Shade Date Open Shade 
December 2..... 19.9 Ce. 15.5 cc.|| December3r.... G27 CG: 4.2 CC. 
- See 16.4 12.4 January 1... at 4-3 
. A 10.8 10.0 . a0. 12.6 6.5 
. oe 12.7 9.2 . hares 12.2 7-8 
Ks ae 22.5 16.2 , Pee 12.0 6.4 
2 ; eee 18.2 12.8 . €52. £8 1.8 
4 ere 15.6 12.0 . O.6. 13.6 8.3 
. e028. 14.4 10.6 « ee 14.1 6.8 
SO: a 15.6 11.3 . eS 12.5 6.0 
= io. e264 16.4 es Oop 6.2 2.4 
. eo 17.0 12.6 - ore: 18.5 8.5 
. Yea 1.4 0.0 . ere 19.8 8.5 
“a Sf 14.8 10.7 4 1S. 22.7 10.0 
ie | EN 18.3 13.5 g 43; 19.4 8.1 
. 16.05. 14.1 10.8 = ee a1.3 9-3 
ea: ie 21.0 15.2 - 15.5 1s:5 6.2 
He 2 Feng 25.2 16.7 . 16.. 13.8 5-9 
. 1 22.1 16.0 . Mis 14.8 5-7 
r eee a2 ¥s.7 . 18. 6.8 1.7 
goo ree 16.6 14.3 . 19.. 13.6 5-4 
. rr pees 13.8 9-5 . a0, 14.4 5-7 
ee 1I.7 7.0 . at 14.6 6.1 
Ss ee 20.2 14:5 . 22.. 15.8 (ee 
gis er. Sonar. 16.3 II.1 « 23. 13.8 6.1 
eo ee 20.7 12.3 : 24.. 12.8 6.0 
go aes ee 21.1 13.3 . a5. 15-3 oe 
. a8 30.3 1 Se ae © 26.. 13.8 6.6 
oe 16.4 16.8 . ae 13.8 6.2 
« BOs. 13.0 8.0 eS 28. 14.4 6.6 
OU ok ck Se a 905.9 sad 
The instruments were set up in such a manner’that the cups were 
about one meter above the ground, the water being supplied to the 
cups by means of burettes. With the growth of the surrounding 
plants the cups were partly shaded, but this was not considered 
6 Lrvincston, B. E., A simple atmometer. Science N.S. 28:319, 320- 1908; S€° 
also Plant World 15:157-162. 1912. 
