316 EEV. G. HE^SLOW ON THE ABSORPTION OE RAIN 



minimum. The internal flow upwards from the root, however, is not 

 at the same time equally checked ; for the temperature of the soil 

 is not lowered to the same extent as that of the air. 



Hence every thing tends to bring the juices to as high a point 

 of saturation at night as possible. Under these conditions one 

 would hardly expect dew to be imbibed in any appreciable quan- 

 tity, unless the leaves and herbaceous stems were exceptionally flaccid. 



Now Duchartre always weighed his plants early in the morn- 

 ing after this statical condition was fully attained ; so that 

 it is not at all surprising to find that he could not detect any in- 

 crease of weight ; hence his experiments seem to prove conclu- 

 sively that at night dew is not usually absorbed in any appreciable 

 degree. 



Dew, however, does not disappear suddenly from leaves at sun- 

 rise ; and it is only after sunlight and heat begin again to affect 

 leaves that the other function of dew is now carried on, its actual 

 absorption. Herein, however, is involved a practical difficulty ; 

 for the balance will no longer help us. But I believe that as 

 soon as transpiration recommences, then any part that may be 

 the first to become dry will now begin to transpire, and so cause 

 an indraught of dew in any neighbouring spot where it may have 

 been retained ; so that there will be an influx and efflux accom- 

 panied by the usual root-supply, which probably furnishes the 

 main source of water for transpiration. Hence it will be seen that 

 it is generally impossible to detect the absorption of dew or rain 

 by leaves with mathematical accuracy or to prove it to demonstra- 

 tion. On the other hand, the " proof" that such is the case may 

 be arrived at indirectly by accumulating probabilities, based upon 

 observed facts. Such is the method I have attempted by aid of 

 the following experiments. 



The conclusion I have arrived at is that, while there is no ob- 

 jection that I know of which cannot be met, there are ample 

 reasons for believing that dew and rain are, under certain circum- 

 stances, absorbed and utilized to supplement the normal root- 

 supply. 



2. Experiments illustrating the Power of Absorption of Water by 



the Epidermis of Herbaceous Internodes. 



A shoot of first year's growth of Elm had three internodes 

 wrapped up in saturated blotting-paper on June 12, 187G. By the 

 15th the leaves were flaccid and nearly faded ; but the terminal 



