IQI2] 



SKINNER— PHOSPHATE AND CU MARIN 



247 



It will be seen that the mainly phosphatic cultures gave a 

 growth in the presence of cumarin which was nearly as good as 

 in the cultures without cumarin. The growth relatively expressed 

 was 98 per cent of the normal. With the other groups it was 84 

 and 89 per cent. The result with the monosodium phosphate is 

 therefore similar to the action of the monocalcium phosphate 

 reported in the earlier paper, a fact which is also shown by the 

 appearance of the plants in the cultures composed of mainly 

 phosphatic fertilizers, the plants having lost entirely the character- 

 istic effect of the cumarin above referred to, an effect which is 



TABLE I 



£CT OF THE MAINLY PHOSPHATIC, MAINLY NITROGENOUS, AND 

 MAINLY POTASSIC FERTILIZERS ON CUMARIN 



Phosphate as monosodium phosphate 



Fertilizers composed of 50 to 



ioo per cent of 



Phosphate 

 Nitrate . . , 

 Potash . . . 



Green weight 



Normal 



With 10 p. p.m. 

 cumarin 



Relative growth (normal 



= 100) 



grams 



39-3 



499 

 46.9 



grams 

 38.6 



42.O 



41.8 



98 



84 

 89 



strongly marked in the cultures low in monosodium phosphate as 

 well as in those low in calcium acid phosphate. This experiment, 

 therefore, disposes quite effectively of the supposition that the cal- 

 cium m the phosphate salt played any significant part in the 

 observed action, since the same action in all particulars is possessed 

 by the monosodium phosphate. There remains the question of 

 the influence or action of the acid character of both phosphates 

 in bringing about the observed result. For this purpose culture 

 experiments in which the acid phosphates were replaced by neutral 

 and even alkaline phosphates were made. 



Effect of disodium phosphate 



The plants in this experiment grew from November i to 12, 

 and the results are presented in table II, the grouping being again 

 made on the basis of the composition of the nutrient salts in the 



