374 SCIENCE PROGRESS 



and was absent from such non-living structures as the coverings 

 of the seed of barley. It now appeared that these coverings 

 were able to effect a complete separation of the water from 

 the acid, and to produce a proportional concentration of the 

 excluded acid solution. Nor is this so in the case of a 5-per- 

 cent, solution only. With solutions of varying strengths, up 

 to 36 per cent., a result accrues which is similar in kind, but 

 different in degree, for as the acid solution becomes more 

 concentrated, less water enters the seed. This difference is 

 to be ascribed to the higher osmotic pressure of the stronger 

 solutions. In short, a seed of barley behaves as a cell com- 

 pletely enclosed in a semi-permeable membrane, this membrane 

 being, as investigation has shown, the inner skin or testa of 

 the seed. The same behaviour of the seed is to be observed 

 when it is immersed in solutions of chlorhydric or phosphoric 

 acid, in dilute alkalies, in solutions of many salts — such as 

 sodium chloride, calcium chloride, cupric sulphate or ferrous 

 sulphate, or in solutions of sucrose, dextrose or glycerine. 



This property of semi-permeability is found to extend to 

 the seed-coverings of all the other species of Gramineae yet 

 examined, and its probable value to the seed is a matter of 

 botanical interest, since a property of this unique character is 

 not unlikely to have some important use. This may consist 

 partly in the benefit which the seed derives from being able 

 to absorb water alone when placed in a moist situation where 

 the soil contains soluble matter likely to injure the seed in 

 the early stages of germination. A more important use of 

 the property will probably be that it serves to retain soluble 

 matter within the grain during fermentation. The starchy 

 endosperm which constitutes the food-reserve of the embryo 

 of seeds of the Gramineae is rendered soluble by enzymic 

 changes in the course of germination ; and it is obvious that 

 if the seed-covering were permeable to such substances as 

 sugar, into which the endosperm is largely converted, much 

 of the food-reserve would be lost by diffusion before it could 

 be absorbed by the young plant. The presence of a semi- 

 permeable covering, on the other hand, ensures the preser- 

 vation of the whole of the food supply to the end designed 

 by Nature. This view of the matter is further strengthened 

 by a consideration of the highly-specialised shape of the seed, 

 with its re-entering ventral furrow, suggesting a necessary 



