SECTIONAL TRANSACTIONS.— K. 493 



Prof. T. A. Bennet-Clark and Miss D. Bexon. — The rSles of osmotic and 

 electrosmotic pressures in the regulation of cell turgor (ii.o). 



The view that cell turgor is maintained solely by the osmotic pressure 

 difference between the vacuole and outside solution is shown to be untenable. 

 For example {a) it is shown that when a protoplast is plasmolysed in potassium 

 chloride of 28 atmospheres and is suddenly transferred to sucrose 28 atmo- 

 spheres, rapid entry of water into the vacuole occurs. Further, when a 

 protoplast plasmolysed in 28 atmospheres is transferred suddenly into 

 53 atmospheres sucrose there is still a rapid passage of water from the stronger 

 external to the loeaker internal solution during a period of approximately 

 10 to 20 minutes, followed by a passage of water out of the cell again in the 

 ' normal ' or expected direction, {b) The data obtained enable us to calcu- 

 late that in addition to the ordinary osmotic flow of water expected on the 

 classical theory water movement at pressures of over 50 atmospheres may 

 be encountered under certain circumstances, (c) In general when a tissue 

 is transferred from an electrolyte solution to one of a non-electrolyte there 

 is a flow of water into the vacuoles which is not due to and may act in the 

 opposite direction to osmotic pressure differences. Similarly if the transfer 

 is from a non-electrolyte to an electrolyte, a non-osmotic flow of water out 

 of the vacuoles is brought about, {d) Study of the behaviour members of 

 the lyotropic series Na — K— Ca — La suggested that these water movements 

 are due to electrostatic forces set up by the ions of the electrolyte, (c) The 

 fact that considerable pressures (possibly electrosmotic) can be generated 

 by a cell of which the osmotic pressure is only about 15 atmospheres 

 suggests that these ' electrosmotic ' pressures may be of great importance 

 in the many turgor reactions of plant tissues. 



Dr. T. G. Mason and Dr. E. Phillis. — Observations on the effects of 

 pressure on the properties of protoplasm (11.30). 



Exposure of cotton leaves to direct pressures of 14,000 lb. per sq. in. in a 

 hydraulic press leads to the expression of a clear sap which is believed to 

 come from the vacuole through fissures in the protoplasm. Only about 

 one-third of the total water of the leaf can be expressed in this way. The 

 rest of the water can be expressed by relatively low pressures provided that 

 the residue is gently rubbed between the fingers and the thumb. It is 

 suggested that protoplasm possesses a gross structure that is destroyed by 

 small shearing forces but which can withstand relatively large direct pres- 

 sures. The residue from the hydraulic press shows approximately normal 

 rates of respiration and can imbibe water till turgor is fully restored. The 

 tenacity with which protoplasm retains its water under direct pressures is 

 contrasted with the ease with which water can be separated from gelatin gels 

 under pressure and it is suggested that the continuous medium of protoplasm 

 cannot be aqueous. 



Dr. Winifred E. Brenchley. — The comparative toxicity of inorganic plant 

 poisons (12.0). 



The majority of elements may exert a harmful action on the growth of 

 higher plants, but the relative proportions necessary vary considerably. 

 Boron and manganese, for instance, may be harmless in quantities at which 

 copper and zinc are intensely poisonous. 



The toxicity of any element may depend upon the compound in which it 

 is presented — e.g. arsenious acid and arsenite proved fatal to barley at 

 concentrations at which arsenic acid and arsenates were innocuous. With 



