The selective permeability of the coverings of the seeds of hordeum vulgare

Abstract

The seeds of the variety of barley known as Hordeum vulgare var. cœrulescens 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 endosperm; 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 concentration 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 containing 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.