Dixon and Atkins — On Osmotic Pressure in Plants. cVc 297 



Table X. 



Syringa vulgaris : leaves. 



During the period of this series of observations, the pressure of the 

 exposed leaves fell from 24'5 to 19'0 atmospheres, while the leaves in the 

 bag were reduced in pressure by 3 atm. below the exposed ones, and this 

 difference is recorded at the end of the series. Strangely enough, in the two 

 cases observed, the percentage of water in the exposed leaves is greater than 

 that in the covered leaves. This fact may be explained by the greater 

 distension of the cells of the leaves wliich contained larger amounts of 

 dissolved substances. This naturally raises the proportion of the liquid to 

 the solid constituents of the leaves, the latter remaining approximately 

 constant during exposure, except for the formation of starch. The high mean 

 molecular weight of the solutes maintained in the shaded samples is 

 surprising. The highest mean molecular weight in the series is recorded 

 for a sample which had been cut off from the light for three days. This 

 seems probably due to the hydrolysis of starch and the formation of maltose, 

 also possibly to the transport of this sugar, or to the formation of the salts 

 of organic acids during respiration. 



