466 Scientific Proceedings^ Royal Dublin Society. 



wfc. 164, agreeing closely in this as in the pressure with C. Limonum. Juice 

 from tlie Tangerine variety, two fruits in February gave 15"51 atm. pressure 

 and mol. wt. 203 ; while after keeping in the laboratory for over three weeks 

 in the dark, the pressure had fallen slightly to 15'24, while the mol. wt. 

 had risen to 231. This high value points to the presence of mono- and 

 di-saccharides in quantity, as well as organic acids. 



It must be borne in mind that the mean molecular weight determinations 

 make no claim to great exactitude ; for example, a solution of pure cane-sugar 

 yielded tlie value 347, the correct chemically obtained value being 342. 



Lycopersicum esculentum (fruit) gave low values from 5-94 to 7"91 atm., 

 the maturer fruits giving the lower pressures, but the higher mean molecular 

 weights, which ranged from 110 to 162, thus again pointed to the absence 

 of quantities of sugars, especially in the less matured samples. 



In Pijnis malm (fruit) much higher osmotic pressures are met with, 17*72 

 to 19'88 atm. The agreement between the values of M is very close, 168 

 and 165 in the sj)ecimens which differed by over two atmospheres in pressure. 

 This same close agreement is found in fruits of Vitis vinifera, M having the 

 values 127 and 128 in pressed juice, although the pressures were 25"64 and 

 27*73 atm. respectively. 



The red stems of Rheum officinale yielded two samples of juice which had 

 an identical value for A, 0'542^ 0. in each case. Here, however, the values 

 of M were 83 and 76, the difference probably being due to experimental 

 error. This very low value is most likely due to the large amount of oxalic 

 acid present in the juice, its mol. wt. being 90, (C00H)2. But its ionization 

 in solution would make its mol. wt. appear to be less. The white bases of the 

 leaves of Apiuni graveolens were also examined and found to have a pressure 

 of 11-36 atmospheres, with low value of M, 125. Sutherst's' datum used by 

 Livingston for calculation gives 12 atm.^ 



Allium Oepa was found by the plasmolytic method to have a pressure of 

 15-21 atm., which is much higher than the specimen examined, 7-97 atm.^ 



Beta vulgaris (root), which was considered to have a high pressure as 

 ascertained by plasmolysis, viz. 15-21 atm.,* was found in the samples used, 

 all from the same source, to vary but little, from 12-52 to 13-11. Here the 

 values of M, 214, 215, 202, denote the presence of large quantities of sugars 

 of the glucose type, mol. wt. 180, and also sucrose, mol. wt. 342, to raise the 

 mean molecular weight. 



1 W. F. Sutherst, Chem. News., 1901, p. 234. 



2 B. E. Livingston, The Eole of Diffusion and Osmotic Pressure in Plants, Chicago, 1903. 

 ' Quoted from Jost's Plant Physiology, p. 419. Eng, Trans., 1903. 



* Quoted from Jost, loc. oit. 



