290 



Sir F. Darwin. 



leaves of the current year were cut under water, and fitted to the Bausch 

 and Lomb (Prof. G-anong's) potometer. The leaves were vaselined and cut 

 as usual, the incisions being usually four in number. The surface of the 

 branch was always carefully greased. 



The first column gives times of observation. The second the number of 

 seconds occupied by the absorption of one degree of the potometer, 

 i.e. of - 01 c.c. The third column (E = rate) gives the reciprocals of the 

 time readings (Column 2) multiplied by 10,000. Thus the hourly rate of 

 absorption (E) is expressed in units of 0-0036 c.c. The fourth column gives 

 the rate E corrected for ty. 



Experiment 20. — June 9, 1913. P. laurocerasus. 



Seven leaves. Eelative humidity (yfr) varying between 58 and 63. 

 Temperature between 1G'5 and 18'3. 



Time. 



Time in seconds. 



E. 



Corrected. 



10.14 A.M. 



Leaves greased. 



Cut : placed at east window. 



10.18 „ 



96 



104 -0 



108 -0 

 (bright day) 



10.26 „ 



102 



98 -0 



98 -0 



10.35 „ 



105 -0 



95 -2 



102 -0 



10.52 „ 



92 5 



108 -0 



115 -0 



11.1 „ 



100 



100 -o 



100 -o 



11.11 „ 



107 -0 



93 -5 



93 -4 



11.16 „ 



107-0 



93 -5 



93 -4 



11.18 „ 



Placed in dark room. 





11.30 „ 



128 



78 -1 



85 -4 



11.42 „ 



141 -0 



70 -9 



77 -5 



11.55 „ 



160 -0 



62 -5 



68 -3 



12.3 P.M. 



161-0 



62 -1 



70 -0 



12.15 „ 



175 -0 



57 -1 



62 -4 



12.20 „ 



Eeplaced afc east window, rather dull. 



12.27 „ 



135 -0 



74 -0 



76 -0 



12.37 „ 



126 -0 



79 -4 



81 -0 



12.44 ., 



110 -o 



90 -9 



94 -9 



If we take the last (corrected) reading in each period we get — 



Light. Dark. Light. 



93-4 62-4 949 



or 150 100 152 



Average: L/D = 151/100. 



The rest of the experiments are given in abbreviated form, i.e., merely the 

 rate E corrected for difference in yjr. « 



