464 Scientific Proceedings, Royal Dublin Society. 



attempt is made to find the relation between the osmotic pressure in plants 

 and their general metabolism. The leaves and other organs yielding only 

 small quantities of liquid have been in part examined by a thermo-electric 

 method;' while the present paper deals with fleshy organs which readily 

 give a plentiful supply of juice. These were treated by means of Raoult's 

 apparatus with a Beckmanu thermometer, about 12 c.c. of juice being used 

 in each determination. 



The zero of the latter was redetermined at close intervals. To avoid 

 freezing out of ice and consequent concentration of the juice, all the precau- 

 tions described in a former paper were adopted.^ 



When the series was almost completed, a copy of Professor Cavara's paper^ 

 was received through the kindness of the author. Cavara examined thirty-two 

 natural orders, determining the depression of freezing-point of their sap, and 

 pointed out how the osmotic pressure could be calculated. His determina- 

 tions were mainly on massive leaves and stems; but some fruits were examined, 

 the changes in pressure on ripening being traced in detail. A few other 

 plant-organs were tested, including two rhizomes. He found an approximate 

 constancy in the similar organs of the same species ; and this is quite in 

 accordance with the results of the present paper. Between different species 

 in the same order there was often a considerable difference in pressure. 

 Many xeropliytes and succulents are included in the list, as well as a number 

 of salt-marsh plants which were shown to have remarkable powers of adapta- 

 tion to the increasing salinity of the lagoon-water during the summer months. 

 With regard to fruits Cavara's results show that, while in some cases the 

 osmotic pressure increases slowly at first, and then very rapidly as maturity is 

 reached, in others the very opposite occurs, there being a marked fall in 

 pressure at maturity. 



The results recorded in this paper add a number of fruits and underground 

 organs to the list of those already examined, and at the same time confirm 

 Cavara's more exhaustive study on the fruits of Vitis vinifera and Citrus 

 Limoniim. 



In the table of results given below, the values of the depression of freez- 

 ing-point are given under A. From the equation P = 12'03 A the osmotic 

 pressure in atmospheres, at 0° C. has been calculated and recorded. As a 



1 " On Osmotic Pressure in Plants ; and on a Ttermo-electric Method of determining Freezing- 

 Points," H. H. Dixon and W. E. G. Atkins, Proo. Eoy. Dublin Soc, vol. xii., N.S., Feb., 

 1910, p. 275. 



2 " Osmotic Pressure of Blood and Eggs of Birds," W". R. G. Atkins, Proo. Boy. Dublin Soc, 

 vol. xii., N.S.. May, 1909, p. 123. 



^"Eisultati di una serie di ricerche crioscopiche sui vegetali," F. Cavara. Coritr. Biol., veg., 

 vol, iv. 



