Studies of Bacillus Radicicola of Canada Field Pea 21 



solution. He concluded from his experiments that nodule development 

 is inhibited by the addition of the following nutrient salts in the given 

 concentrations : 



Alkaline nitrates, concentration 1 to 10 , 000 

 Ammonium salts, concentration 1 to 2,000 

 Potassium salts, concentration 1 to 300 

 Sodium salts, concentration 1 to 200 



The influence of phosphates was variable, and calcium and magnesium 

 salts stimulated nodule development. Marchal was of the opinion that 

 the variation of the osmotic pressure, due to the presence of the different 

 salts, may be the cause of this phenomenon. 



Moore (1905) states that the addition of 1 per cent of sodium and 

 potassium salts often entirely inhibits the formation of nodules, and 

 smaller quantities considerably reduce their formation. The addition of 

 calcium and magnesium salts, on the other hand, greatly favors nodule 

 formation. Moore states further that this is not true with all the legumes, 

 since the addition of calcium and magnesium carbonates is injurious 

 to the formation of nodules on lupines and other plants adapted to 

 acid soil. 



In the following experiments the influence of various factors on nodule 

 production has been investigated. The factors studied are light and 

 darkness, aeration, moisture, various concentrations of nutrient solutions, 

 and a considerable number of chemical substances. 



E3fPERIMENT 1 



influence of aeration in light and in darkness 



In this experiment Canada field peas were grown in an aqueous soil 

 extract. The extract was prepared by taking one part of soil and four 

 parts of water, by weight. The mixture was allowed to stand for two 

 hours, and the liquid was then decanted and filtered. Twelve Erlen- 

 meyer flasks of 300 cubic centimeters capacity were filled, and one pea 

 was planted in each flask. Six of the flasks were covered with black paper 

 and the other six were exposed to diffused light. Three flasks n each' 

 of the two series were aerated by passing a current of air through the 

 liquid during the entire experiment. All the plants were inoculated with 



