60 TRANSPIRATION IN A DESERT PERENNIAL. 
The seals of the pots were not broken in the meantime. This day proved 
to be continuously clear, with practically no air movement. The results 
appear in table 24. No. 6 showed a drop and rise in both actual and relative 
transpiration, being of much less magnitude in the former case than in the 
latter. No. 7 behaved very much as on April 2, the maximum for actual 
transpiration coinciding with that of evaporation, and the maximum for 
relative transpiration occurring earlier. . 
ee 
a a oe a ae a ee er a ae 
Fic. 26.—Graphs for transpiration of plant No. 6, under 
two different conditions of evaporation. Exp. XXTI. 
Under conditions of high evaporation thus far, No. 6 has shown a morning 
drop and rise and No. 7 has not. The next plan was to put No. 7 under 
conditions of still higher evaporation and No. 6 under conditions of lowered 
evaporation. On April 11 the natural conditions provided greater evapo- 
ration than was obtained on either of the previous days, as the sun was 
bright and the wind velocity extremely high during the entire day. In 
order to secure the desired conditions for No. 6, a wooden box large enough 
to hold plant, atmometer, a Lambrecht’s polymeter, and a thermometer 
was lined with wet towels; an opening was left in the side and top of the box 
for the entrance of sunlight and air. The towels were wet frequently and 
