io6 



This may be illustrated 



LECTURE VII. 

 by some of Garreau's results : 



The mode in which Garreau conducted the experiments of which 

 these are the results has been recently criticised by von Hohnel. 

 Garreau determined the amount of water given off by the increase of 

 weight of some chloride of calcium which was placed in a receiver 

 together with the leaf. Von Hohnel points out that the chloride of calcium 

 in the lower half of the receiver is under more favourable conditions 

 than that in the upper half for absorbing the moisture exhaled by the 

 leaf. In an experiment made in this manner with Coleus Blumei, he 

 found the relative transpiration of the two surfaces to be i : 8. In a 

 second experiment, he reversed the position of the leaf so that the true 

 lower (dorsal) surface transpired into the upper half of the receiver : 

 he now found the relative amount of moisture absorbed by the chloride 

 in the upper to be to that absorbed by the lower as i : 4*6. It appears 

 therefore that the differences determined by Garreau are too great. 



From the foregoing table it appears that although the 

 surface with the greater number of stomata transpires the 

 more freely, yet there is no sort of proportion between the 

 number of the stomata and the activity of the transpiration. 

 Von Hohnel has, however, repeated Garreau's experiments 



