1909.] 



Coverings of the Seeds of Hordeum vulgare. 



89 



It will be noticed that the gain in weight in presence of the iodide is 

 markedly greater than in presence of the chloride or sulphate, but that none 

 of the salts has so considerable an effect as sodium chloride. 



In the case of the seeds steeped in the solution of cadmium iodide — a salt 

 which is supposed to be very slightly dissociated when dissolved in water — 

 small quantities of the salt diffused through the coverings ; cadmium was 

 not detected, however, in the seeds which had been steeped in solutions of 

 either the chloride or the sulphate, which are supposed to undergo dissocia- 

 tion to a somewhat limited extent, although to a greater extent than the 

 iodide. 



Acetic and other Weak Acids. — On searching for compounds capable of 

 passing through the seed-coverings, when it was found that acetic acid 

 possesses the property, it at first seemed probable that the acid might be 

 capable of destroying the semi-permeable layer of the seed. Seeds were 

 therefore steeped in solutions containing both acetic and sulphuric acids or 

 acetic acid and cupric sulphate ; in both cases only acetic acid and water 

 diffused through the coverings. 



Water also passes freely together with the acid into the seeds. The 

 results of experiments with a volume normal solution of the acetic acid 

 are recorded in Table V ; it will be noticed that the acid has but a slight 

 influence in diminishing the amount of water which is absorbed when 

 equilibrium is established. 



Table V. 



Solute. 



Percentage of water 

 absorbed. 



Acetic acid 



Water (control) 



Sodium acetate (control) 



73 -8 

 78 -2 

 39 "8 



On examining the behaviour of the seeds towards organic acids other 

 than acetic, it was found that formic, propionic and butyric acids also 

 enter the seed system, and that they affect the introduction of water much 

 as acetic acid does. 



Glycollic acid, although excluded during about 48 hours, subsequently 

 diffuses slowly into the seed. Lactic acid did not enter most of the grains 

 until after the lapse of 72 to 96 hours. The amount of water absorbed by the 

 seed is diminished more by these acids than by acetic acid, thus : — 



