302 



Scientific Proceedings, Royal Dublin Society. 



Table XVI. 



Syringa vulgaris : leaves. 



Here two reasons may be adduced as principally responsible for the rise in 

 pressure, viz., (1] the liydrolysis of starch and tlie production of maltose ; and 

 (2) the inversion of cane-sugar into dextrose and levulose. Unfortunately 

 no determination of the mean molecular weight of the (a) sample was made, 

 and consequently we are unable to decide between these two alternatives. 



A similar rise in pressure on keeping lias also been observed in leaves 

 which have not been exposed to light for twelve days. 



Table XVII. 

 Syringa vulgaris : leaves twelve days in dark bag. 



In this case the rise of the mean molecular weight indicates that the 

 rise in the osmotic pressure is due to the formation in the leaves of some 

 disaccharide, probably maltose from the hydrolysis of starch. Observations 

 53 and 54, Table XVIII., favour this view. These were made on leaves 

 taken from an overshadowed position, and which consequently had not the 

 opportunity of storing appreciable quantities of carbohydrates. As was 

 expected, the overshadowed sample did not give tiie usual rise in pressure on 

 keeping. Presumably they contained neither starch to hydrolyse nor cane- 

 sugar to invert. The consumption of dextrose in respiration was probably 

 accountable for the slight fall in pressure observed. 



