ii2 TRANSPIRATION AND ASCENT OF SAP ch. 



of the maximum cohesion of boiled sap. The results 

 quoted happen to be the first obtained. Other experiments 

 were not made, as these are sufficient to demonstrate that 

 the boiled sap possesses cohesive properties of the same 

 order as those of water. 



Having found that sap, free from unwetted nuclei, but 

 saturated with air, is able to sustain considerable tensions, 

 it seemed worth while trying if unboiled sap could be put 

 into the tensile condition. The consideration that heating 

 the enclosed sap in the glass envelope until the last visible 

 bubble disappeared would probably remove completely all 

 invisible bubbles encouraged me in this attempt. Accord- 

 ingly a quantity of sap was collected from a branch of 

 Ilex aquifolium by means of centrifuging ; and this after 

 exposure to air and without any special treatment was 

 introduced into several capillary tubes, which had been 

 prepared in a manner similar to those used in the other 

 experiments. 



The first tube closed at a temperature of 78'2, and 

 ruptured on cooling to a temperature of 72*0 (see 

 Experiment No. 7 in Table 11). This rupture occurred 

 simultaneously with a slight shock accidentally dealt it by 

 the stirrer of the vessel of water in which it was immersed. 

 Had it not been for this, probably a lower temperature 

 would have been attained without rupture. Taking these 

 figures and the dimensions of the tube into account, the 

 tension developed must have been about 75 atmospheres. 



Another tube containing some of the same sample of 

 sap completely filled at a temperature of 91 10 C. On 

 one occasion rupture took place only when a temper- 

 ature of 76*2 was reached, on another a rupture 

 developed at some temperature below 81*5. In the 

 latter case, when the tube had fallen to 8l'5, it was 

 withdrawn from the water for examination, and rupture 

 occurred some seconds after it was lifted from the water. 

 In the first instance the tension must have approxi- 



