in ASCENT OF SAP IN STEMS 71 



the bottom of a metal cistern, about 65 cm. deep. The 

 upper ends of the branches projected above, and the lower 

 ends below, the cistern. The joints round the lower ends 

 were rendered water-tight by binding on a rubber tube 

 overlapping the tubulures and the projecting ends of the 

 branches. The cistern was then filled with water which, 

 being in motion, secured that both branches were at the 

 same temperature, and so differences in viscosity in the 

 water passing through the branches did not arise. 



In order to avoid irregularities in transmission, much 

 care is needed in the preparation of the branches. After 

 selection of the branches, the upper leafy part was cut 

 away, and the cut surface of the lower part still attached 

 to the tree was moistened by a jet of water. This part 

 was then cut off under water, and while still submerged, 

 was removed to the laboratory. Fresh surfaces were next 

 prepared at each end, and smoothed off by a razor, under 

 a stream of distilled water. A wide glass tube about 

 20 cm. long was attached to the upper end of each branch. 

 This was kept full of distilled water, which acted as the 

 supply and head, driving the water downwards through 

 the branches. If it was desired to apply picric acid or 

 some other poison as a killing agent, the simple glass tube 

 was replaced in each case by one which was provided with 

 a side tubulure, bent in a J form, and with two stop-cocks 

 placed as shown in Fig. 13. 



The rate of transmission from above downwards was 

 first observed for the two branches by weighing the amount 

 of water transmitted in a given time (say 10 min.). It is 

 evident if vital actions were at work tending to raise the 

 water in the branches, the rate of flow downwards would be 

 reduced by this activity ; and inasmuch as both branches 

 are under similar conditions, the reduction of flow would 

 be the same for both. It may here be noted that an altera- 

 tion in the head of 10 cm. makes a very sensible difference 

 in the amount transmitted, raising it, to take an example, 



