DEPARTMENT OF BOTANICAL RESEARCH. 83 



gradually developed a precipitate in the form of a suspension, con- 

 sisting in part of the iron salt, but in no case has this proved disad- 

 vantageous in the conduct of the experiments. 



In general, this series of cultures has exhibited remarkable vigor and 

 an intensity of green which contrasts strongly with the other cultures 

 made at the same time, in which the concentration of iron is much less. 

 Maximum growth occurred in those cultures in which the partial 

 volume-molecular concentration of the salts was as follows: KNO3, 

 0.0099; CaS04, 0.00155; MgS04, 0.00115; and soluble ferric phosphate 

 0.25 gm. per 1,000 c.c. This represents the maximum concentration 

 of all salts employed, but at the same time it represents in all proba- 

 bihty approximately the most favorable concentrations in which these 

 salts may be used, inasmuch as previous work under conditions of high 

 evaporation had indicated a falling off in the growth-rate when con- 

 centrations above this were employed. 



The next more favorable group of results are those in which the iron 

 salt and the magnesium are reduced to one-half concentration, the 

 calcium and potassium remaining at maximum. A slight increase in 

 magnesium with diminution in the amount of calcium has invariably 

 resulted in a much lower growth-rate. In these experiments there has 

 been no notable increase in the growth quantity as a result of the 

 addition of aluminium, and it is quite probable that this is related to 

 the fact that in no culture is the amount of iron as low as in the usual 

 salt solutions recommended for the growth of wheat. 



A second group of experiments has included a solution of iron, 

 nrngnesium, and potassium salts as mentioned above, in minimum 

 quantities, with calcium supplied as monobasic calcium phosphate. 

 In this case, however, the growth quantities are as low as the minimum 

 of the preceding group, and increasing the magnesium and potassium 

 salt to a maximum quantity has afforded little additional growth 

 increase. 



Comparisons have been made between the solution first discussed 

 and one consisting of monobasic calcium phosphate, potassium nitrate, 

 and magnesium sulphate, with the addition of iron either as the sul- 

 phate or as the soluble ferric phosphate, in both cases supplied in the 

 amount usually recommended, namely, 0.0044 gram per liter of solu- 

 tion. Such solutions have yielded growth quantities comparable only 

 with the poorest cultures in the group first discussed. 



Elaborate experiments are now in progress to determine the influence 

 of various proportions of iron in the form of the soluble ferric phosphate 

 contrasted with the insoluble ferric pho.sphate in solutions consisting 

 of (1) monobasic potassium phosphate, calcium nitrate, and magnesium 

 sulphate; (2) monobasic calcium phosphate, potassium nitrate, and 

 magnesium sulphate; (3) calcium sulphate, potassium nitrate, and 

 magnesium sulphate (the phosphate in this case being supplied only 

 in the form of the iron salt). 



