THE CARBOHYDRATES OF THE ANGIOSPERM LEAF 23 



One as yet unnoticed deduction from the above table is 

 that it points to a progressive increase in osmotic pressure 

 as the season advances even though the total percentage 

 of sugars may remain unchanged. This follows because for 

 a given weight of sugar a hexose exerts nearly twice as great 

 a pressure as sucrose, owing to its smaller molecular weight. 

 The assumption is here made that the sugars are dissolved 

 in equal weights of water, which is approximately true, for 

 the leaf cells are always almost fully distended. Part of 

 the increase in osmotic pressure with the age of the leaf, 

 attributed by Dixon and Atkins (1912, 2 and 3) to the 

 accumulation of salts, may possibly be due to this change 

 in the nature of the stored sugars. 



DIURNAL CHANGES IN THE SUGARS OF THE SNOWDROP. 



The analyses of beet leaves by Girard previously quoted 

 are quite paralleled by those obtained by Parkin for the 

 snowdrop, for he finds that during any single day of the 

 spring the percentage of hexose sugars in the leaf remains 

 fairly constant, no matter what hour out of the twenty -four 

 the leaves may be examined. The sucrose, on the other 

 hand, fluctuates greatly. It increases during the day and 

 diminishes during the night. Further, leaves detached 

 and insolated contain decidedly more sucrose than their 

 controls. Parkin performed comparative sets of experi- 

 ments on the following : 



(a) Leaves picked in the morning with those gathered in 

 the afternoon. 



(6) Leaves picked in the evening with those gathered the 

 following morning. 



(c) Leaves detached from the plants with those attached, 

 both being kept in the dark overnight. 



(d) Leaves detached and insolated with those left 

 attached 



