306 



Scientific Proceedings^ Royal Dublin Society. 



Physiology of Foliage Leaves, the amounts of the various sugars found 

 immediately on gathering leaves of Tropceolum majus, and the amounts 

 determined after the leaves had been kept twenty-four hours in darkness. 



Allowing 342 for the molecular weight of cane-sugar and maltose, and 

 180 for that of dextrose and levulose, and calculating the number of gram- 

 molecules of these sugars present as a measiu-e of osmotic pressure, we find 

 in the first experiment the number changed from 0'0436 gram-molecules 

 when gathered to 0'0381 gram-molecules after twenty-four hours in dark. 

 This change would evidently cause a fall in the osmotic pressure. In Brown 

 and Morris's second experiment the ratio of the number of gram-moleculea 

 is 0-0411 to 0-0419 after twenty-four hours. This would, of course, pro- 

 duce a rise of pressure, and would quite parallel our pair, 66 and 68, 

 where the osmotic pressures before and after twenty-four hours' darkness 

 were 14-61 and 14-76 atmospheres. 



Considered from the point of view of the osmotic pressures. Brown and 

 Morris's analyses are extremely interesting, as showing that it is possible for 

 the osmotic pressure to remain steady when the total percentage of the sugars 

 varies considerably, and vice versa. 



Taking a general survey of the experiments on Syringa vulgaris, we see 

 tliat the highest pressure observed in the leaves freshly gathered was, at the 

 end of August, 26-87 atmospheres (experiment 6). This observation was 

 made by means of the early arrangements, in which the sap was diluted, 

 and possibly is not so reliable as the determination obtained on the pressed 

 sap. The result, however, is supported by experiment 45, iu which undiluted 

 sap was used. The pressure estimated in the latter experiment was 24-57 

 atmospheres. That both these pressures might, under conditions particularly 



