24 Scientific Proceedings, Royal Dublin Society-. 



of flow downwards is reduced by this activity ; and inasmuch as both 

 branches are under similar conditions, tlie reduction of flow is the same 

 for both. It may here be noted that an alteration in the head of 10 cms. 

 makes a very sensible difference in the amount transmitted, raising it, 

 to take an example, from 0'450 gram to 0'500 gram per 10 min. If 

 now one branch be killed, the vital lifting-force, if present, will be removed, 

 and we should expect the amount transmitted by the killed branch to increase 

 correspondingly. This increase, even though small, would be easily seen by 

 comparing the flow through the dead and the living branches, when both 

 have been again brought to the same conditions. For killing the branch I 

 used either a jacket of steam or an injection of poison. 



When it is desired to kill the experimental branch with steam, the water 

 in the cistern is run off through a small side-tubulure (c), and, when the 

 cistern is empty, steam is passed by the same tubulure into a wide tube [d), 

 now placed round the experimental branch, and fitting tightly into a socket 

 made for its reception in the bottom of the cistern. The space round the top 

 of this branch, and between it and the tube, is packed with eotton-wool. The 

 supply of steam is kept up for 20 min. ; the tube (d) is then removed ; and 

 the cistern is filled with water through the tubulure (c). After some time, 

 during which the water in the cistern is kept stirred, when it is judged that 

 the experimental and control branches have come to sensibly the same 

 temperature, measurements of the amounts transmitted by each may be 

 resumed. In this way it is easy not only to compare dead and living branches 

 under the same conditions, but also rough manipulation and shaking is 

 avoided. These latter are known to cause irregularities in the amounts of 

 water transmitted by cut branches, probably owing to the displacement of 

 or compacting of some clogging material on their upper surfaces. 



Observations made in this way showed in each case that the amounts 

 transmitted by a branch before and after killing by steam were sensibly the 

 same ; or if they differed in the experimental branch, the same difference was 

 observed in the amounts transmitted by the control branch at the same time, 

 the observable differences being due to changes in conditions which affected 

 the fiow in the living as well as in the killed branch. 



In Table 1. is recorded au example of one of these experiments, which is 

 graphically recorded in fig. 2. 



