Physiologie. 191 



pressure of the developing buds, young leaves, and mature leaves. 

 A table is given showing the series of determinations of the de- 

 pression of the freezing point, the osmotic pressure calculated from 

 it, and the mean molecular weight of dissolved substances. The 

 steady rise in osmotic pressure in the buds during February and 

 March is attributed to the transport of dissolved substances into 

 them as well as the Solution of previously undissolved substances 

 already present; the rapid increase in size of the leaves in April 

 was accompanied by a falling-off in pressure in the growing leaves, 

 attributed to dilution of the sap b}^ the predominance of water ab- 

 sorption over accumulation of dissolved substances; but at the end 

 of April assimilation and transpiration more than counterbalanced 

 water absorption, and from then onwards the pressure continued 

 to increase; finally a diminution was registered in the leaves just 

 about to fall, attributed to transport of materials from the leaves. 



F. Cavers. 



Dixon, H. H. and W. R. G. Atkins. Osmotic pressures in 

 plants. I. Methods of extracting sap from Plant Organs. 

 (Sei. Proc. Roy. Dublin Soc. XIII. (N. S.). 28. p. 422—433. 1913.) 



The authors show that the sap pressed from living untreated 

 tissues does not give a true estimate of the concentration of that in 

 the vacuoles of the cells of the organ before the application of 

 pressure. In order to extract the sap from the cells without altering 

 the concentration, it is necessary to render the protoplasmic mem- 

 branes permeable. This can best be effected by the application of 

 liquid air. S. G. Paine. 



Dixon, H. H. and W. R. G. Atkins. Osmotic pressures in 

 Plants. II. Cryoscopic and Conductivity measure- 

 ments ofsome vegetable Saps. (Sei. Proc. Roy. Dublin Soc. 

 XIII. (N. S.). 29. 1913.) 



The discovery in paper abstracted above makes it necessary to 

 revise all cryoscopic or electrical conductivity determinations where 

 expressed sap has been employed. The authors repeat their own 

 measurements of osmotic pressure making use of sap pressed imme- 

 diately after thawing from tissues frozen solid in liquid air. 



These determinations show that their earlier estimates were too 

 low and hence that the actual osmotic pressures in the cells are 

 much greater than the requirements of the cohesion theory of the 

 ascent of sap demand. S. G. Paine. 



Dixon, H. H. and W. R. G. Atkins. Varia tions in the os- 

 motic pressure ofthe sap ofthe leaves of Heder a Helix. 

 (Sei Proc. Roy. Dublin Soc. XIII. 19. p. 239-246. 1912.) 



These observations were made simultaneously with those on 

 Hex recorded in the preceding paper. Two series of measurements 

 were made — from plants growing in a north aspect and in a 

 south aspect respectively — in order to determine the effect of 

 direct sunlight on the osmotic pressure. Tables are given, also a 

 curve showing the results obtained at intervals during two years 

 from the two series of observations. The cryoscopic value of the 

 sap of the south-aspect leaves is consistently greater than that of 

 the leaves from the north aspect; the average depression of freezing- 



