156 University of California Publications in Agricultural Sciences [Vol. o 



a balanced solution, since the addition of either magnesium or cal- 

 cium chloride resulted in an increased growth of the pea seedlings. 



In the present investigation there are only two cases in which the 

 growth of the plants was greater with both calcium and magnesium 

 chlorides present than when calcium chloride was used alone in vari- 

 ous concentrations, one in culture 6, series 2, the other in culture 11, 

 series 3. In the latter culture the dry weight of the plants was twice 

 that in the same concentration of calcium chloride alone. There are 

 marked differences in growth recorded between different combinations 

 and concentrations of the two salts, and as can be easily seen from 

 the graphs, the percentages of the two ions found in the plants show 

 an inverse relation to growth in nearly every instance. Proceeding 

 from series to series, the amount of magnesium found in the plants 

 increases with the concentration of the magnesium chloride in the 

 nutrient solution. 



Magnesium sulphate is not as toxic as magnesium chloride in 

 equivalent concentrations of the kation. Growth in solutions of mag- 

 nesium sulphate plus calcium chloride was superior in every case to 

 that found when the salts were used separately. There is a marked 

 contrast between calcium chloride and calcium nitrate in antagoniz- 

 ing the toxic effects of magnesium sulphate, the nitrate proving less 

 effective than the chloride in concentrations of .12 M. and over. This 

 is of especial interest, since the qualitative ionic relations of the nutri- 

 ent are not altered. It is possible that we are dealing with the effects 

 of undissociated molecules in the higher concentrations, which may 

 be very different from ionic effects. 



Results with Salts of the Heavy Metals 



Since salts of aluminum, copper, zinc, iron and mercury were 

 used, it will be necessary for the sake of clearness to treat each more 

 or less separately. 



Miyake 33 has shown aluminum chloride to be highly toxic, in con- 



N 

 eentrations above , to rice seedlings grown in water cultures. 



Similar results have been reported by House 34 and Gies. Micheels and 

 De Heen, 35 Duggar, 30 and Ruprecht, 37 working with several aluminum 



33 Jour. Biol. Chem., vol. 25 (1916), p. 23. 

 34Amer. Jour. Physiol., vol. 15 (1905), p. 19. 

 35 Bull. Acad. Roy. Belg. (1905), p. 520. 

 30 Plant Physiology, New York, Macmillan, 1911. 

 37 Mass. Exp. Sta. Bull. 161 (1915), p. 125. 



