162 University of California Publications in Agricultural Sciences [Vol.3 



as the ratio of these two ions in the solution becomes narrower. 

 "Where a wide ratio exists in the solution, there is always a much nar- 

 rower ratio in the plants. 



From the brief discussion above it is evident that the barley plants 

 grew equally well in solutions having widely different ratios of cal- 

 cium and magnesium ions. There is no "optimum lime-magnesia 

 ratio," as Gile 46 and "Wyatt 47 as well as others have shown, and their 

 results are confirmed in the present investigation. 



The balance between all the ions present in the solution appears 

 to be of far greater importance than any single ratio. A considera- 

 tion of the ratios existing between the various ions of the nutrient 

 solution, aside from calcium and magnesium used, is reserved for 

 further study. 



Permeability and Antagonism 



It is not proposed to enter into a discussion of the structure and 

 composition of the plasma membrane. Davidson 48 has recently sum- 

 marized our present knowledge concerning it with special reference 

 to selective permeability. A discussion of the various theories which 

 have been advanced to explain antagonistic salt action need not be 

 taken up in detail here. The reader is referred to papers by Clark, 49 

 Loeb, 50 Osterhout, 51 Loew, 52 Koenig and Paul, 53 True and Gies r ' 4 , True 

 and Bartlett, 55 Kearney and Cameron, 65 and Ostwald 57 , for a discus- 

 sion of the various factors which may be of importance in this con- 

 nection. 



The recent work of Clowes 58 and Fenn 50 is important and some 

 very striking similarities between the action of toxic and antagonistic 

 solutions on oil emulsions and on gelatine on the one hand, and plant 

 cells on the other, have been reported by these investigators. 



46 Porto Rico Exp. Sta., Bull. 12 (1912). 



47 Jour. Agr. Research, vol. 6 (1916), p. 589. 



48 Plant World, vol. 19 (1916), p. 331. 

 49Bot. Gaz., vol. 33 (1902), p. 26. 

 soArchiv. ges. Physiol., vol. 88 (1902), p. 68. 

 "Science, n.s., vol. 35 (1912), p. 112. 



52 Flora, vol. 75 (1892), p. 368. 



53 Zeitschr. Hygiene u. Infektionskrankheiten, vol. 25 (1897), p. 1. 



54 Bull. Torr. Bot. Club, vol. 30 (1903), p. 390. 

 ss TJ. S. Dept. Agr., Bull. 231, 1912. 



56 U. S. Dept. Agr., Bull. 71, 1902. 



57 Archiv. ges. Physiol., vol. 120 (1907), p. 19. 

 5* Jour. Phys. Chem., vol. 20 (1916), p. 407. 

 5»Proc. Nat. Acad. Sci., vol. 2 (1916), p. 539. 



