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. 



7 8 9 10 11 12 1 2 3 4 5 6 



Fig. 26. Graphs for transpiration of plant No. 6, under 

 two different conditions of evaporation. Exp. XXI. 



Under conditions of high evaporation thus far, No. G 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 1 1 the natural conditions provided greater evapo- 

 ration than was obtained on either of the previous days, as the sun was 

 bright and the Avind 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 



