694 Physiologie. 



and sodium arsenate though in less degree; no Stimulation was 

 evident with the smallest quantities tested. Boric acid is less poiso- 

 nous than zinc sulphate or arsenic Compounds, especially with peas; 

 barley shows apparent Stimulation with some of the weaker strengths; 

 but this is not borne out by the dry weights, whereas peas are defi- 

 nitely stimulated with relatively high concentrations, the action of 

 the greater strengths being well marked in the leaves which tend 

 to turn brown and die. F. Cavers. 



Dixon, H. H., Note on changes in the sap caused by the 

 heating of branches. (Sei. Proc. Roy. Dublin Soc. XIV. p. 

 224—228. 1914.) 



The author has demonstrated experimentall}^ by cryoscopic and 

 conductivity measurements, and by various chemical tests, the 

 changes which might be anticipated in the sap of the conducting 

 tracts of a branch by the rendering permeable of the plasmatic 

 membranes and the consequent discharge of the contents of the 

 adjoining cells. Sap centrifuged from a heated branch was found to 

 be four to six times more concentrated than that similarly extracted 

 from a living branch. This change in concentration of substances 

 not rapidl}?- absorbed would acl as a physical poison on the cells of 

 the leaves borne on the branch and would alone explain the chan- 

 ges observed in the leaves. It was also found in four cases out of 

 tive that the sap of a steamed branch acted as a protoplasmic 

 poison to the cells of Elodea leaves, while during the same period 

 the sap from fresh branches was harmless. F. Cavers. 



Dixon, H. H., Note on the spread of morbid changes 

 through plants from branches killed by heat. (Sei. Proc. 

 Roy. Dublin Soc. XIV. p. 207—210. 1914.) 



Experiments are described showing the possibility of washing 

 out the poisonous materials liberated in the water tracts of branches 

 killed by heat, and thus removing the contamination from the water 

 supply of the leaves above. The withering of the leaves on a killed 

 branch may in this way be long postponed. It is also possible to 

 wash back the contaminating substances from the dead branch into 

 other branches, when it is found that the leaves on the otherwise 

 uninjured branches wither. These experiments are held to show 

 that the withering cannot be assigned to failure in water supply 

 brought about directly \iy the dcath of the cells of the heated 

 branch. F. Cavers. 



Dixon, H. H., On the tensile strenght ofthe sap oftrees. 

 (Sei. Proc. Roy. Dublin Soc. XIV. p. 229—244. 1914.) 



Some authors have stated that while water sensibl)^ free from 

 dissolved air has no considerable tensile strength, such cohesion 

 cannot be demonstrated in the sap of trees. The author had nega- 

 tived this Statement from his previous experimental work, but he 

 now gives the results of direct tests of the tensile strenght of sap. 

 Experiments were raade on sap centrifuged from the branches; 

 Berthelot's method of generating tension was used, but allowance 

 was made for the distortion of the containing tube during the expe- 

 riment. It was found easy to generate tension in both boiled and 



