MACDOUGAL--ACTION OF LIPOIDS IN GROWTH. 37 



possibility of the action on other colloids than proteins and Hpoids is 

 not considered. Kahho pubhshed the results of his tests as to the 

 permeability of roots of yellow lupine to neutral salts late in 1921. 

 He confirms the series as to permeability of kations which runs 

 K>Na>Li>Mg>Ba>Ca, in which the greatest penetrability is 

 shown by potassium and the least by calcium. It is also seen that the 

 interferences are such that each kation is retarded by those to its 

 right, and to a degree proportionate to its distance to the right, and 

 that the greatest retardation is by the kations which show the greatest 

 coagulating action on colloids. The kations which have the least 

 coagulating action on colloids penetrate most rapidly. The anions 

 retard the colloidal or coagulative action of the kations in a series, 

 citrate <sulphate< tartrate <C1<N03< Br < I, in which the effect is 

 least with the citrate and most with the iodine. That is, each kation 

 has the greatest effect when combined with the citrate and least with 

 the iodine. As a further consequence, the citrates have the least 

 penetrability and the salts of iodine greatest. It is held that the be- 

 havior of the roots in a weak alkaline solution supports the conclusion 

 of Hansteen-Cranner as to a lipoidal layer.'^ The greater expansion 

 and contraction of growing roots in weak alkaline solutions is attrib- 

 uted to the solution or displacement action of such solutions on the 

 lipoidal meshwork of the walls, rendering them more contractile. 



The results cited above are not decisive or final when taken sep- 

 arately. Their concurrence lends substantial support to the conten- 

 tion that the lipoids are a prime factor in the exchanges between the 

 cell and the medium. The establishment of the fact that such a lipoid 

 as lecithin may be present as an emulsion consisting of a disperse 

 medium soluble in water and of a disperse phase swelling in water, 

 the entire system displaceable by fat-solvents, would furnish a plas- 

 matic membrane or peripheral layer through which both salts and 

 fatty substances might diffuse. Lecithin, for example, is supposed 

 to absorb about 40 per cent, of its volume in hydration in water, is 

 soluble in chloroform, alcohol, benzene, carbon disulphide, etc., and 

 has the power of combining with both acids and bases. 



" Kahho, H., " Ein Beitrag zur Permeabilitat des Pflanzenprotoplasmas 

 fiir Neutralsalze," Biorhem. Zeit., 120: 284-303, 1921. See also p. 125, same 

 volume. 



