70 
Deherain also arranged the following experiments showing the 
effect of temperature. Some living leaves of wheat were kept within 
a glass tube which lay in a water bath at a uniform temperature of 
15° C. and the following measurements taken : 
In full sunshine the transpiration was 0.939 gram of water per 
hour per gram weight of leaf. 
In darkness the transpiration was 0.016 gram of water per hour 
per gram weight of leaf. 
The water bath was then reduced to a temperature of 0° C., and the 
temperature of the leaf within the tube must therefore have been at 
the freezing point. In this condition the transpiration in full sun- 
shine was 1.088 grams of water per hour per gram weight of leaf. 
Thus leaves in sunshine in free air'at 28° C. and leaves in the 
air at 15° C., and again in the water bath at 0° C., give us the tran- 
spiration under these conditions 0.882, 0.939, 1.088, respectively. It 
is evident that this transpiration is not due to evaporation alone, else 
it would be independent of sunshine and depend wholly on heat; the 
decided differences here shown must be attributed to the special 
excitement of the cell by the solar radiation. 
Marie Davy gives for July 24 and 25, 1877, the following record 
from a self-registering apparatus showing the diurnal periodicity of 
the transpiration from the leaves of four plants of haricot beans 
which were watered daily at 7 p. m.: 
Diurnal periodicity of transpiration. 
Riou [Beano gta, 7 ease | 9 ices ea eee 
WetorSepeamis me. seen cee AO 4scolora meee nee eerse S| | LEGO FA nye ee eee 120 
8 to9 p. m__- E 2) ||hOsbO Grane sees reas Brin | ees ovis iq Oss AO 95 
Oetoe Ola Bee ee 2) (6 toian maeesns ee 465) |t3 Cords pares 67 
JOOS pam == soee 4a MigtOxSias Mae anes ee 99) || 45bodp am S22 2a 44 
11 p.m. to1l2midnight- | NSxtO19 fan ee ee 86))|\-5toiGsp sams =e 25 
12 midnight tola.m_-_ 4 | 9 ton Oaemis see 128 | 6itoWepsm: hos eee 10 
ADR ORE Fah 0 eh eee ae 2) lO tor tases eee 153)||iGtO Sap sina eee 4 
Pan Oy yelp 08 Ole, oe el eae ae 4 || 11 a. m. to 12 noon _-_- 179 
Sto aia bth ae ee 4 || 12 noon tol p. m_---- 143 
These same four plants showed the transpiration day by day, as 
given in the first column of the following table (Marie Davy, 1880, 
p. 239). The third and fourth columns, respectively, show the rela- 
tion of this transpiration.to the daily mean temperature and the daily 
mean radiation, as shown by the conjugate thermometers. 
