Permeability of Coverings of Seeds of Hordeum vulgare. 83 



hydrogen chloride, the colour remained unaltered, showing that there is no 

 diffusion of acid into the grain. 



Solutions of caustic soda containing 1 per cent, or more of alkali disintegrate 

 the seed covering ; this resists the action of the alkali, however, if the liquid 

 contain only | per cent., and after steeping seeds during several days in the 

 solution, although water diffuses into the grain, no alkali enters. 



Salts such as cupric sulphate, ferrous sulphate, potassium chromate, and 

 silver nitrate were all found to be impenetrant substances. 



Up to this point, it appeared that the covering of the seeds was a perfect 

 " semi-permeable " membrane. Using iodine dissolved in a solution of 

 potassium iodide, however, observations were made which indicated that the 

 membrane possessed the power of selection — iodine was found to pass slowly 

 into the seed until after several days it permeated the whole of the starchy 

 endosperm, staining it a deep blue colour. That this result was not a conse- 

 quence of the destruction of the membrane was proved by steeping seeds thus 

 impregnated with iodine in a solution of sodium thiosulphate. So long as 

 the seed coverings remained intact the iodine was unaffected, but when the 

 coverings were ruptured the thiosulphate diffused rapidly into the seeds 

 decolorising the iodine. 



At this point my earlier studies were directed to an investigation of the 

 nature and position of the particular covering of the seed of H. vulgare., which 

 acted as the " semi-permeable " membrane. The experiments already 

 described demonstrate that the embryo and endosperm of the seeds are 

 enclosed within an envelope through which water and iodine diffuse readily, 

 but through which salts and strong acids do not diffuse. As there appeared 

 to be no recognised instance in the vegetable kingdom of a membrane other 

 than one composed of living protoplasm possessing marked " semi-permeable " 

 properties, it was obviously desirable to ascertain if the selective permea- 

 bility of the seed- coverings were a function of the living tissue. From the 



as faulty. Subsequently, the corns which remained blue were steeped continuously in the 

 acid, and observed from time to time, with the following results : — 



Time 

 of steeping. 



Percentage of corns 

 remaining blue. 



3 days 



100 



5 „ 



99 



? , A : 



95 



10 „ 



89 



14 „ 



74 



19 „ 



25 



24 „ 



1 



G 2 



