THE CABBOHYDBATES OF THE ANGIOSPEBM LEAF 11 



Here the rise, owing to insoJation, is very marked viz., 

 from 17-12 to 25-68 atmospheres. Some of this must be 

 attributed to concentration by loss of water, as at the end 

 of the experiment a few of the leaves had begun to wilt. 

 The last column, however, shows that this concentration 

 can only account for a small portion of the observed rise, 

 from 17-12 to 18-66 atmospheres. It is interesting to see 

 that the mean molecular weight of the sap solutes hardly 

 alters at all, for sucrose and maltose have identical molec- 

 ular weights, 342, whilst that of glucose and fructose is 180. 

 Other constituents of the sap lower the mean, as values far 

 below those of the sugars are frequently obtained. The 

 diminution of osmotic pressure is not, of course, a measure 

 of the total consumption of carbohydrates during darkness, 

 for hydrolysis of starch keeps up the supply of maltose. 

 From the table of sugar analyses just quoted it may be 

 calculated that the ratio of the number of gramme molecules 

 of the sugars present before and after twenty-four hours in 

 the dark is 0-0411 to 0-0419 respectively. This would, of 

 course, produce a rise of pressure, and would quite parallel 

 a similar experiment by Dixon and Atkins in which the 

 osmotic pressures before and after twenty -four hours' 

 darkness were 14-61 and 14-76 atmospheres. In another 

 table given by Brown and Morris the alteration in molecular 

 concentration of sugars is from 0-0436 to 0-0381 after 

 twenty-four hours, which accordingly causes a fall in 

 osmotic pressure. Table V. which follows further illus- 

 trates these changes. The leaves were picked, and each 

 leaf was halved. The halves were then employed in the 

 comparative experiments. 



The most striking result is that the osmotic pressure in 

 the control has not varied at all, though from the work of 

 Brown and Morris it is certain that a complicated series of 

 changes has been taking place in the leaf sugars. The 



