142 SOME RECENT RESEARCHES IN PLANT PHYSIOLOGY 



no passage of sodium chloride through the membrane occurs, 

 though other substances are able to penetrate. 



The capability or incapability of a substance to enter 

 the seeds was judged by the amount of water taken up by 

 them from various solutions, which were usually gramme- 

 molecular. 



The results are well summarized in the table opposite, 

 quoted from ShulTs work. 



The table shows that as a class the nitrates penetrate 

 the coats. This is especially so in the case of silver nitrate. 

 Ferrous sulphate enters slowly, but copper sulphate 

 penetrates only to a very slight extent. Mercuric chloride, 

 iodine in potassium iodide, the monohydroxy alcohols, 

 ether, the alkalies and acids, enter with rapidity from 

 aqueous solution. The penetration of hydrochloric and 

 tartaric acids is only slight, whilst that of sulphuric also 

 is very slow. To glycerol and the sugars the membrane is 

 impermeable. 



Since neither boiling nor treatment with iodine or 

 mercuric chloride alters the semi-permeability of the 

 membrane towards sodium chloride, it is evident that 

 this property depends, not on living cells, but upon the 

 chemical and physical properties of the cell walls. 



Shull has recorded that a number of other seed coats 

 also behave as semi-permeable membranes, and gives the 

 list which follows: Alismaceae (Alisma plantago-aquatica), 

 Graminese (barley, wheat, oats, etc., probably most grasses), 

 Chenopodiacese (sugar beet), Rosaceae (peach, apple), Legu- 

 minosae (Vicia faba, scarlet runner, Lima bean), Com- 

 positae (Xanthium glabratum, Helianthus annuus}. These 

 however, vary considerably m their degree of semi-perme- 

 ability, and some of the number permit of the passage of 

 salts to a noticeable extent. 



