Ill 



ASCENT OF SAP IN STEMS 



65 



through the dead portion. Subsequently, it was twice 

 filtered, and supplied to cut branches. These latter faded 

 in two and a half days, while controls did not show signs of 

 fading for several days later. 



Removal of Contamination. It has been found 

 possible to confirm this explanation of the fading 

 of the leaves in another very striking manner. It 

 was to be expected that if poisonous materials gene- 

 rated by the application of heat in the supporting stem 

 caused morbid changes in the leaves above, it should be 

 possible partially or completely to prevent the changes 

 by washing out these materials from 

 the stem as they are formed. We 

 should expect the leaves above such a 

 heated and washed-out stem to last 

 fresh much longer than those above 

 a similar piece of stem which had been 

 heated but was not washed out. 



The experiment was performed on 

 a pot plant of Prunus cerasus. The 

 stem of this plant, at a level of about 

 40 cm. above the soil, bifurcated into 

 two equal branches, B and C (see 

 Fig. 11). B produced two lateral 

 branches, E and D, at 11 and 34 cm. 

 respectively above the bifurcation, 

 while C had two smaller leafy branches 

 about 15 cm. above the bifurcation, 

 and terminated with a tuft of leafy 

 branches above. The top of B above 

 the base of D was removed, and, with suitable precautions 

 to minimise clogging, a rubber tube was attached 

 to it. The whole of E, except a few centimetres of its 

 base, was cut away. The cut surface at the top of 

 B was now supplied with distilled water under a head of 

 33 'cm. When the cut surface of E, by becoming moist, 



F 



Fig. 11. 



