74 TRANSPIRATION AND ASCENT OF SAP ch. 



20 min. When the cistern was refilled and stirred, the 

 measurements were resumed. 



Table 7. 



Immediately after the experimental branch is surrounded 

 with steam, the water transmitted through it becomes 

 coloured, at first amber, changing to brown. 1 This change 

 probably indicates the introduction into the transmitted 

 water of some clogging material ; for, instead of 

 an increase in the amount transmitted downwards 

 after the removal of the supposed vital lifting forces, 

 we see from the table that the amount is diminished. 

 According as the downward stream washes out this sub- 

 stance, the original rate of transmission is approximated 

 to, but, during the experiment, is not attained. It is 

 evident that if there was any considerable length of branch 

 below the steamed part, this material would accumulate 

 there. 



The small rise in the amount transmitted by the control 

 branch, noted immediately after the observations were 

 renewed, is probably to be attributed to a rise in tempera- 

 ture and consequent reduction of viscosity. 



The effect of steaming on the experimental branch, and 

 the uniform behaviour of the control, are clearly brought 

 out in Fig. 14, in which the ordinates are grammes of 



1 The production of the brown colour [may with probability be assigned 

 to the action of the oxydases of the stem on a colourless chromogen 

 before the enzymes^were destroyed by heat. 



