42 



TRANSPIRATION IN A DESERT PERENNIAL. 



Experiment XVI. 

 The subject of this experiment was an adult tree, called B, growing about 

 20 feet from tree A. Transpiration rate was determined by the calcium 

 chloride method described on page 10, and the evaporation was determined 

 by the use of atmometer of type 2 (C, fig. 2) under a separate l)ell-jar. The 

 area of the branch used was not determined, so that the T here represents 

 actual losses and not losses per unit area. Figure 20 gives the values for 

 V/uj plotted with the values for T/E. 



Table 18. 



-Relative transpiration and stomatal openings from an adult tree. 

 Experiment XVI. Date, August 23, 1911. 



Experiment XVII. 



Method, Lloyd's for measurement of stomata. 



Subjects, plants Nos. 1 and 2, and atmometer No. 10, brown. Situation, 

 in the open, exposed to sun and wind. Conditions, soil-moisture conditions 

 were made to correspond as nearly as possible to those of July 27 and August 

 5. No. 1 had been without water 5 days, while No. 2 had received the usual 

 amount. The leaves of No. 1 had the same curled appearance as on August 

 5, while No. 2 appeared in all respects normal, as on July 27. At the close 

 of the experiment, No. 1 responded to water as on August 5. The percent- 

 age of soil moisture was determined as before and appears in the tables. In 

 this experiment only the widths of the openings of the stomata are given, 

 since the curve of widths has been found to correspond in shape to the curve 

 of V/w. All measurements were taken in the bright sunlight unless other- 

 wise stated. At 6*^ 30"" a. m. and 12'' 30'" p. m. measurements were also 

 made in the shade and appear on the curves as isolated dots above the corre- 

 sponding hours. To the left of the curve appear again, reduced one-half, 

 the relative transpiration rates for plants Nos. 1 and 2 under similar con- 

 ditions of soil moisture. So far as can be told from the evaporation readings 

 for the 3 days, the evaporation conditions were similar. 



Table Id. Comparison of stomatal operiings of potted plants under different 

 conditions of soil moisture. E.vperiment XVII. Date, August 20, 1911. 



Time. 



6i>30a.m 



9 

 10 

 11 



12 



I 



00 

 00 

 00 



30 



00 



a.m 

 a.m 

 a.m 



p.m 



p.m 



f shade. . 



\sun. . . . 



, sun 



, sun 



, sun 



f shade. . 



\sun. . . . 



* Soil-moisture of No. 1 =3.6 p. ct. 



t Soil-moisture of No. 2 = 14.2 p. ct. 



' Cloudine-ss prevented further readings. 



