452 Scientific Proceedings. Royal Dublin Society. 



August -September, the osmotic pressure of Ilex is very low at that period, 

 reaching its observed minimum in the former month. Its maximum is in 

 spring, and there is another period of high pressure in autumn. 



The graph traced by the concentration of carbohydrates in the leaves 

 of Ilex differs in its form from that of Syringa, but it shows, as in 

 Syringa, that the major part of the sohites are carbohydrates, and 

 that consequently they are chiefly responsible for the osmotic pressures 

 in the cells. Further, to the fluctuations in the amounts of these 

 substances are due the large variations in the osmotic pressure. The 

 fact that the greatest concentrations are found in spring and autumn 

 may indicate that the photosynthesis of this evergreen is most 

 efficient in light of a moderate intensity, whilst the leaves of a deciduous 

 plant, like Syringa, are most active during the period of more intense 

 illumination; some such an adaptation for each is quite conceivably 

 advantageous where a maximum amount of carbon assimilation is desirable. 

 These considerations also possibly suggest an explanation of the greater 

 irregularity of the curves in the winter sections. The fluctuations then 

 probably correspond to fluctuations in the intensity of the light. In the 

 summer the optimum intensity is nearly always exceeded, and the limit of 

 activity residing in the leaves themselves determines a more uniform 

 production of carbohydrates. The smaller fluctuations then may be referred 

 to want of uniformity in consumption and translocation. 



The dotted graph which traces the osmotic pressure of 'sap pressed from 

 untreated leaves follows, in a general way, the graph obtained from the 

 frozen leaves, but is, as is usual, lower than it. 



The figures in Table III demonstrate plainly that, just as in the case of 

 Syringa, there is a concentration of electrolytes in the sap of the leaves with 

 age. In this table the means of all the observations on the leaves of the 

 different growths are entered, and the number of observations thus averaged 

 is given in the top line. It may be seen that, while there is a decided 

 increase in the concentration of the electrolytes, from the youngest to the 

 oldest, the concentration of the total solutes does not show such a rise, nor 

 does that of the carbohydrates. 



The osmotic pressure, of course, is dependent on the fluctuations of the 

 total solutes. 



