61 



The soil from plot 31 nitrified dried blood much 

 more etriciently than ammonium sulphate. However, 

 ammonium sulphate caused nearly twice as much man- 

 ganese to go into solution as did the dried blood. 

 Anmionium sulphate retarded nitrification in the soil 

 from plot 32, but increased the amount of manganese 

 in the solution. Incubation of this soil without ferti- 

 lizers of any kind, increased the amount of soluble 

 manganese from 21 to 37 p. p. m. of solution. 



In every case, the peas grown in the untreated soil 

 extracts showed a tendency to bleach; the untreated 

 extract from plot 32 produced plants that were almost 

 white. Those extracts to which calcium carbo^nate 

 was added made a good growth of both roots and tops; 

 but even here, bleached leaves were found, and the 

 entire foliage was of a lighter green color than that of 

 plants grown in the solution to which caustic potash 

 had been added. According to McCooI (12), such 

 bleaching is a characteristic cfTect of manganese. Had 

 these cultures received direct sunlight, instead of the 

 subdued light from glazed windows, it is very probable 

 that the injury to the tops would have been much more 

 severe. 



As shown in Table XII, the extract of the soil from 

 plot 31 which had been incubated with dried blood 

 contained 22 p. p. m. of Mn., and 200 p. p. m. of NO^. 

 The original air dry soil from plot 32 gave an extract 

 with 21 p. p. m. of Mn., and 18 p. p. m. of NO.,. With 

 the same manganese content, these two extracts differ- 

 ed widely in toxicity. Each supported a fair root 

 growth; but the tops of the peas grown in the extract 

 from plot 32 were highly abnormal in development, 

 and were almost white. Since these extracts contained 

 widely different amounts of nitrates, it was thought 

 possible to explain the difference in toxicity on the 

 basis of the difference in calcium content. Therefore, 

 after the cultures w^ere taken down, quantitative cal- 

 cium determinations were made on these, and on sev- 

 eral other untreated extracts. And the less toxic extract 

 with the high nitrate content, was found to contain 60.2 

 p. p. m. of Ca., while the more toxic extract contained 

 only 22.0 p. p. m. of Ca, Incubated with sulphate of 

 ammonia, soil from plots 31 and 32 gave extracts with 

 identical amounts of manganese. But the extract from 

 plot 31 was not nearly so toxic toward pea roots as 

 was the extract from plot 32. The difference in the 

 calcium content of the two extracts again offers an 



