180 Scientific Proceedings, Royal Dublin Society. 



Transpiration into a Water-saturated Atmosphere; on Transpiration into 

 various vapours and gases ; on Transpiration in Dead Branches ; on the 

 Tensile Strength of Water ; on the Tensile Strength of Sap, and on the 

 Strength of Cell Walls ; also on the resistance experienced by the transpira- 

 tion stream. In these researches he further established the Tension 

 Theory, and replied to criticisms on it ; and he showed that the cells of the 

 leaf have often an active part in applying the tension to the sap, and that 

 the tension is transmitted downwards through the tree, and raises the sap in 

 the stem without the intervention of forces exerted by the living cells of the 

 stem. 



A careful and laborious research on the temperature of the underground 

 organs of plants carried out by means of thermocouples, in 1902, showed that 

 such organs possess no detectable proper heat. A similar method of research 

 was subsequently applied by Dixon to the determination of the freezing point 

 of the sap of leaf-cells. He was thus enabled to determine with ease the 

 osmotic pressure of these cells in many plants, and so to define their function 

 in the raising of the sap. He had previously partly solved this problem by 

 a direct method which had to be abandoned on account of the personal risk 

 attending its use. 



The thermo-electric method of cryoscopy thus devised has been extensively 

 used by Dixon, in collaboration with Dr. W. E. G. Atkins, in the investiga- 

 tion, not only of the sap of leaf-cells, but of that of other organs, and much 

 information as to the concentration of the sap in stem, root, and leaves has 

 been obtained. The method has also afforded valuable information in their 

 hands as to the constitution of the sap of the Transpiration Stream and 

 respecting the obscure subject of root-pressure. They have shown that the 

 Transpiration Stream has functions to perform in the distribution of carbo- 

 hydrates as important as those in connexion with the transport of water and 

 of mineral solutions in plants. The thermo-electric method has also proved 

 efficient in studying the metabolism of the yeast cell and the changes brought 

 about by it in wort. 



In these researches it was found that the usual methods of extracting 

 cell-sap did not yield an average sample of the tissues treated, and so a 

 serious error in the cryoscopic investigations of previous workers was 

 detected. At the same time it was shown that this error might be avoided 

 by exposing the tissue under experiment to intense cold and so rendering the 

 protoplasm permeable. This has proved a most useful observation, and has 

 furnished a ready method for extracting enzymes from cells : often a problem 

 of great difficulty. For example, an active preparation of zymase may be 

 obtained by this method in a few minutes. 



