82 



The Selective Permeability of the Coverings of the Seeds of 

 Hordeum vulgare. 

 By Adrian J. Brown, Professor of Brewing in the University of Birmingham 



(Communicated by Prof. H. E. Armstrong, F.R.S. Eeceived January 23, — 

 Eead January 28, 1909.) 



The seeds of the variety of barley known as Hordeum vulgare var. 

 ccerulescens owe their colour to the presence of a blue pigment in the aleurone 

 cells ; this pigment, like litmus, is turned red by acids. Such seeds, when 

 immersed in a dilute solution of sulphuric acid, if their coverings are damaged, 

 soon turn pink in colour, which is a proof that acid diffuses into the endo- 

 sperm ; sound seeds, on the other hand, although they imbibe water freely 

 from the solution, becoming soft and swollen, retain their colour, showing that 

 the covering has the property of resisting the passage of the acid, whilst it 

 allows water to diffuse freely into the interior of the grain. So much is this 

 the case that a dilute solution of sulphuric acid may be concentrated by 

 steeping barley in it. Thus in an experiment with a solution containing 

 4 - 9 grammes of acid per 100 c.c. it was found that the concentration of the 

 acid was increased to 7' 6 grammes per 100 c.c. In another case, in which 

 the weight of water absorbed was ascertained, it was observed that the con- 

 centration effected was in direct proportion to the amount of water absorbed 

 by the seeds. 



Having made the discovery of so remarkable a " semi-permeable " 

 membrane, I have endeavoured to ascertain its behaviour towards substances 

 generally. In my earlier experiments, of which an account has been given 

 elsewhere,* it was found that sulphuric acid could not penetrate into the 

 grain, not only from volume normal solutions, but also from solutions con- 

 taining 9, 18, or even 36 grammes of acid per 100 c.c. In the case of the 

 seeds immersed in the strongest acid, however, the interior remained dry, 

 presumably because the power of the seed contents of imbibing water was 

 insufficient to overcome the osmotic pressure of the liquid. 



The vitality of the embryos was not destroyed by steeping the seeds in the 

 acid solutions ; when placed under suitable conditions they all germinated.f 



When the blue seeds were immersed in a volume normal solution of 



* ' Annals of Botany,' vol. 21, p. 79, 1907. 



t Recent observations show that the barley corn displays a most remarkable power of 

 withstanding the action of sulphuric acid. A number of blue corns, i.e., those containing 

 the neutral indicator for acid, were steeped in a volume normal solution of sulphuric acid 

 during 48 hours, those corns which showed traces of red after this treatment being rejected 



