120 Prof. A. J. Brown and Mr. F. Tinker. Absorption of 



regulated, in the main, by the osmotic pressure of the solution in which the 

 seeds are immersed — a condition normal to the behaviour of any semi- 

 permeable diffusion system. 



On the other hand it has been demonstrated that with solutions of those 

 solutes which are able to diffuse through the seed membrane there is a 

 general tendency not only for more moisture to enter the seeds than from 

 pure water itself, but also for the rate of entry of the moisture to be 

 accelerated to an extent varying with both the nature of the solute and the 

 concentration of its solution. 



The factors controlling the rate of entry of moisture into the seeds 

 provide a promising subject for investigation, but so far the influence of 

 temperature only has been studied. It has been shown in a previous com- 

 munication* that the rate of entry of moisture into the seeds from both pure 

 water and solutions of permeable and impermeable solutes is an exponential 

 function of the temperature with a very high coefficient closely approxi- 

 mating that of vapour pressure, and also of a number of chemical reactions 

 occurring in solution. But this conclusion provides no explanation of the 

 interesting observation that the rate of entry of moisture into the seeds from 

 solutions of permeable solutes varies with the nature of the solute when 

 the solutions are at constant temperature and of equimolecular concentra- 

 tion. Presumably the explanation of this is to be found in the variation in 

 the physical properties of the different solutes when in solution, and it was 

 with the object of discovering, if possible, with which of the physical 

 properties of the solutions the rate of absorption is associated, that the 

 present research was undertaken. Such properties as are likely to exert an 

 influence on the absorption rate are evidently ionisation, osmotic pressure, 

 vapour pressure, viscosity, and surface tension. 



Preliminary experiments showed that the phenols would form a most 

 suitable series of solutes for the purpose of the present comparative study. 

 The membrane of the barley seed is permeable to them all ; they show 

 striking differences among themselves with regard to some of their physical 

 properties, whilst other of their properties are almost equal, and they have 

 a negligible ionisation when in solution, so that consideration of this latter 

 factor is eliminated when dealing with them. The solutions chosen for the 

 present research accordingly comprised those of phenol, catechol, resorcinol, 

 quinol, and pyrogallol. 



Three series of comparative experiments were made with the above 

 phenolic solutions : — 



(a) In the first series samples of seed were steeped in seminormal 

 * Brown and Worley, loc. cit. 



