438 



Scientific Proceedings, Royal Dublin Society. 



the requirements of the coliesion theory of the ascent of sap. Even tlien the 

 values obtained were, in all cases, ample. Now, tlie newer and more accurate 

 figures tabulated above show that our earlier estimates were too low, and 

 hence tliat the actual osmotic pressures in the cells are much greater than that 

 demanded by the theory. 



A survey of the table shows that the range of the osmotic pressures observed 

 in the saps extracted by the liquid-air method is as large as that recorded by 

 us and others for those obtained from the untreated organs. Tlie highest, so 

 far observed, is that for the fruit of Vitis vinifera, viz., 38*32 atm. (A = 3'185°), 

 and the lowest for the leaf of Saccharum officinanim, viz., 5"83 atm. (A = 0'588°). 



The following abstracts show in what plants the maxima and minima for 

 the various organs have been found, and also record the values ascertained. 

 Our previous determinations have, however, given us higher values in several 

 instances. We now know that even these were underestimates. 



Reference to the table of results will sliow that the leaves of Hedera Helix, 

 taken from a north aspect, have on the average a smaller depression of freezing- 

 point (1'233°, mean of tliree observations) than those taken from a south 

 aspect (1"308°, mean of six observations). A similar difference had been 

 found for the untreated leaves. 



Again, just as in the ease of the untreated leaves oi Ilex Aquifolium, those 

 frozen in liquid air showed a concentration of their sap with age. 



In the same way the general trend of the results obtained by the use of 

 sap extracted by the old method (2, 3, 4, 5) has been confirmed by the 

 observations made on that from organs treated with liquid air. Thus, it 

 will be seen that in the same plant, e.g., Iris gennanica, the osmotic pressure 

 in the root is less than that in the rhizome, while the pressure in the latter 



