v TENSILE STRENGTH OF SAP OF TREES in 



days in water, heating and cooling being effected in the 

 same water. The tube was emptied before each boiling, 

 and allowed to fill with the freshly boiled water. The 

 .object of this was to wet the tube thoroughly, and any 

 dust-particles it contained, by bringing all undissolved air 

 on their surfaces into solution. The tube, after filling with 

 the sap to within a few millimetres of its end, was sealed 

 off. The heating of the tube was effected, as in my pre- 

 vious work, in a large volume of water, and was very slow. 



In the first tube submitted to experiment the air- 

 bubble disappeared at 63*5, which may be described 

 as the " closing ' temperature, and reappeared with the 

 characteristic click at 59 1. Three other observations 

 were made with this tube. All four agree in indicating that 

 the sap withstood a tension of more than 45 atmospheres 

 before rupture (cp. Experiments 1, 2, 3, and 4 in 

 Table 11, p. 113). 



A second tube was charged with some of the same 

 sample of sap ; it was found to become completely filled 

 at 66*2, and ruptured at 59*5. Calculating the tension 

 developed in this case the result is more than 70 atmo- 

 spheres (see Experiment 5 in the Table). In another 

 experiment with this tube a tension of about 50 atmo- 

 spheres was produced (see No. 6). 



It was thought that possibly, by keeping one of these 

 tubes after closing at a temperature close to that at which 

 the bubble disappeared, greater tensions might be attained. 

 This surmise was not realised. The tube used in the first 

 experiments described above was kept for two days at a 

 temperature of about 61. However, when ultimately 

 allowed to cool slowly, the rupture occurred at 59*2, a 

 temperature not quite so low as had sometimes before 

 been successfully passed. This experiment is recorded as 

 No. 3 in Table 11. 



It mav be noted that there is no reason to believe that 

 the tensions produced in these experiments are indications 



