296 



Scientific Proceedings, Royal Dublin Society. 



Similarly the osmotic pressure iu leaves gathered after a dull day is 

 lower thau after a bright one, as appears from the foUowiug observations. 



Table VIII. 

 Syrhuja nilgariis : leaves 



As might be e.\pected from the foregoing, and as has already been seen 

 in the ease of Ulmus, leaves taken from a position naturally overshadowed 

 are found to have a lower pressure tlian those taken from au exposed 

 position. 



Table IX. 



8yri.nga vulyaris : leaves. 



The effect of assimilation may also be easily observed, by comparing the 

 freezing-points of the sap of exposed leaves with that of leaves in a similar 

 position, but shaded by an opaque cover. We obtained many results 

 illustrating this. In the following table the leaves giving the (a) samples 

 were surrounded by an opaque paper bag at 10 a.m., September 15; at 

 intervals samples were taken out and examined. The (j3) samples were 

 furnished bj' neighbouring leaves imder similar conditions, but not covered. 



