154 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



PRESSURES DUE TO ELECTROLYTES AND TO NON- 

 ELECTROLYTES. 



In the following table, compiled from the work of Dixon 

 and Atkins, the freezing-point A is shown for the sap of 

 various leaves, pressed after treatment with liquid air. 

 In addition P, the osmotic pressure in atmospheres cal- 

 culated from A, and C, the electrical conductivity in 

 mhos at 0, are shown. Furthermore, in order to record the 

 osmotic pressure due to electrolytes, the column under 

 A e shows, as already explained, the depressions of freezing- 

 points of solutions of potassium chloride having the con- 

 ductivities shown in the column C. The column A A e 

 contains the values of depression of freezing-point occa- 

 sioned by non-electrolytes. 



Almost all these determinations were carried out in the 

 late autumn or winter ; accordingly but few of the pressures 

 found exceed 20 atmospheres, though in previous work, 

 in which the freezing-point only was measured in each case, 

 values up to 30 atmospheres were found. Those plants 

 marked with an asterisk were growing in greenhouses. 

 In some of the latter very low pressures were met with, 

 and in producing them electrolytes were preponderant as 

 a general rule, whereas in the case of plants under average 

 conditions of assimilation in the open air in Ireland the 

 reverse is the case, most of the pressure being due to non- 

 electrolytes. The increase in the quantity of electrolytes 

 in old leaves as compared with young leaves under similar 

 conditions is well shown by the values of A e for Ilex aqui- 

 folium and Populus alba. 



It is remarkable that the only Pteridophytes examined, 

 Equisetum, Polypodium, and Selaginella, have unusually 

 high conductivities, and that the major portion of the 

 osmotic pressure of their cells is due to electrolytes. 



