1909,] Vegetable Assimilation and Respiration. 31 



Table XVII. 



Julv 22 



25-3 



„ 24 



26 -6 



„ 26 



24 -4 



„ 27 



23 -8 



„ 30 



27 -6 



August 3 



22 -2 



Maximum 

 temperature in 

 degrees C. 



Weather. 



Average percentage 

 decrease in area 

 of Leaves I — IV 



between 5 a.m. and 

 3 P.M. 



Clear 



Hazy 



Bright : white clouds 



Clear, changing to rather cloHdy, 

 then hazy 



Clear : some wind 



Clear 



Average of all six days 



3 7 



Applying such a medium correctiou to Sachs' result, we obtain the 

 following : — 





Sachs' results. 



Results " corrected " 

 for shrinkage. 



Dry weight of 700 sq. cm., 5 a.m 



grammes. 



grammes. 



3 054 



3-054 



3 P.M 



3 -693 



3-556 





0-639 



0-502 



Gain per square metre per hour 



0-914 



0-717 



If 0'7 gramme is really the true result, Sachs' value was too high by 

 0'2 gramme, i.e. by about 30 per cent. 



Brown and Morris, in their repetition of this experiment under similar 

 weather conditions, terminated it two hours later than Sachs.* It is possible, 

 therefore, that their smaller result is to be accounted for by the fact that 

 their experimental half-leaves had had two hours longer in which to recover 

 from shrinkage.-f 



Sachs' experiment with RheumX is also liable to a great error. In this case he com- 

 menced at 6 A.M. and ended the experiment at 11 a.m. after five hours of prevailing 

 sunshine. He obtained for the gain of dry weight per square metre per hour the value 

 0-652 gramme. 



In one of my experiments, when the sunshine was only intermittent, four marks were 

 made on a large Rhubarb leaf, roughly in the positions which would be occupied by the 



* Loc. cit., p. 627. 



f It may not be entirely fortuitous that their result, 0-713 gramme per square metre 

 per hour, agrees closely with the value 0 7 obtained above by introducing a correction for 

 shrinkage into Sachs' result. 



% Loc. cit., p. 24. 



