Dixon — Transpiration into a Saturated Atmosphere. 633 



In carrying out this experiment, of course, care must be taken tliat 

 the gas-pressure in the branch has become equalized with that of the 

 atmosphere. With this precaution, however, the result seems con- 

 clusive, i.e. that pumping actions, and not evaporation cause the rise 

 of the eosin into it. 



It Tvill be found that, if the water in the receiver is warm 

 (25°-30° C), and if the apparatus is placed in a strong light, the 



Fig. 2. 



ascent of the eosin will be rapid ; if, on the other hand, the water is 

 cold (below 12° C.) and the light is not strong, the eosin will rise 

 but slowly in the branch. If the apparatus is placed in darkness, the 

 eosin will rise but little or not at all. 



It seems probable that the increased rate is, in part, due to the 

 quickening of the vital processes due to the rise in temperature when 

 the water suiTounding the leaves is warm. 



