298 



Sir F. Darwin. 



Results. 



§ 1. The method employed was to close the stomata by carefully rubbing 

 the stomatal surface with cocoa-fat or vaseline, the intercellular spaces being 

 afterwards put in communication with the outer air by means of incisions. 



In the case of leaves not thus treated, it is well known that the closure of 

 the stomata in darkness greatly diminishes the evaporating surface and 

 vice versa. In my method the evaporating surface is a constant. 



§ 2. The following tables give the comparative effects of diffused daylight 

 and darkness on the transpiration of P. laurocerasus and Hedera helix treated 

 as in S 1. 



P. laurocerasus. 



Date. 



Light. 



Dark. 



Date. 



Light. 



Dark 



1911. 







_ 



1913. 







April 11 



105 



100 



May 14 



101 



100 



„ 19 



100 



100 



„ 17 



185 



100 



» 20 



148 



100 



„ 22 



134 



100 



„ 22 



123 



100 



„ 24 



201 



100 



1913. 







„ 25 



June 6 



7 



151 



100 



April 21 



May 3 



| 113* 



100 



185 

 154 



100 

 100 



„ 3 



116 



100 



„ 9 



151 



100 



5 



107 



100 



„ 12 



126 



100 



6 



125 



100 



» 13 



126 



]00 



7 



114 



100 



„ 16 

 1911. 



138 



100 



7 



134 



100 







8 



100 



100 



Nov. 15 



125 



100 



„ 10 



105 



100 



17 



114 



100 



,, 10 



159 



100 



1909. 







12 



120 



100 



Dec. 9 



119 



100 



» 12 



144 



100 









Average L/D : 131 '7/100, in round numbers 132/100 or 32 per cent. 



# The average of eight experiments, see p. 286. 



Ivy {Hedera). 



Date. 



Light. 



Dark. 



Date. 



Light. 



Dark. 



June 22, 1913 

 July 1, „ 

 4, „ 



174 

 138 

 136 



100 

 100 

 100 



July 7, 1913 i 

 „ 9, „ 

 „ 10, „ 



113 

 121 

 131 



100 

 100 

 100 







Average L/D : 



136/100 or 36 per cent. 







§ 3. The tables given under § 2 show a remarkable degree of variability : 

 the extreme cases are : April 19, 1911, when the result was nil, and May 24, 



