Dixon — Transpiration into a Saturated Atmosphere. 629 



gas pressure existing in tlie water conduits has become equalized 

 to that of the atmosphere, and that, consequently, the external 

 pressure exerted at the base of the branch has ceased to move the 

 water upwards. An open beaker, containing water at 100°C., is now 

 introduced under the receiver, and the branch is transferred from the 

 water to a watery solution of eosin. A wooden screen is set to cut 

 off the direct radiation of the beaker from the branch. These arrange- 

 ments are made in a dull light, and, when complete, the whole is 

 set in total darkness. 



As soon as the beaker containing the hot water is introduced under 

 the receiver, the space included will immediately be filled with cloud 

 and water vapour, Water is freely deposited on ihe walls of the 

 receiver and on the surfaces of the leaves of the plant. The space is 

 completely saturated, and remains so, as it continues to fall in tem- 

 perature, owing to the gradual cooling of the whole ; and, as the 

 water is always at a higher temperature than the leaves, a constant 

 distillation goes on from the beaker to the leaves. The arrangements 

 are shown in figure 1 . 



Fig. 1. 



"When these arrangements have been made the apparatus is left 

 for one hour. At the end of this time, it will be found that the eosin 

 solution has been drawn up very markedly into the plant, thus 

 showing that the elevation of the water in the conduits may be 

 effected by vital action. For in this experiment the immediate 

 energy relations of the plant to its surroundings cannot account for 

 the rise. I have performed this experiment, with the same result, 

 with Chrysanthemum sinense, C. lacustre, Myrtus communis, Eucalyptiis, 

 ffhhulus, Escallonia macrantha. 



