20 Martin J. Prucha 



Hiltner (1900) showed that the addition of potassium nitrate to the 

 nutrient solution in which legumes are grown has an injurious influence 

 on nodule development, and he thinks this is due to the fact that the 

 formation of bacteroids in the small nodules is hastened by the presence 

 of the nitrate. He considers the bacteroids as degenerate and inactive 

 forms of the nodule-forming organism. 



A somewhat more extensive investigation of this subject was under- 

 taken by Nobbe and Richter (1902). They attempted to determine the 

 influence of potassium nitrate and of humous substances on the fixation 

 of nitrogen by soy beans. They grew the plants in flowerpots in a rich 

 soil and in a poor soil. For rich soil they used garden soil. The poor 

 soil was prepared by mixing 4000 grams of sand and 2500 grams of garden 

 soil. Potassium nitrate was added to the poor soil in the proportions of 

 500 and 1000 milligrams to 6500 grams of the soil. When the plants 

 were harvested the total amount of dry substance and of nitrogenous 

 matter was determined in each plant. The results of this experiment 

 show that the function of the nodules for nitrogen fixation is injured to 

 a high degree by the presence of potassium nitrate. The influence of 

 humous substances is similar, but not so great. 



The observation made by Frank, by Nobbe and Richter, and by others 

 — - namel}'', that soil rich in humous substances has a deleterious effect on 

 nodule development — was confirmed also by Moore (1905). He grew 

 soy beans in rich nitrogenous soil, in poor clay soil, and in poor sandy 

 soil. Very few nodules developed on trie soy beans grown in rich soil, 

 while in the poor clay soil and in the poor sandy soil the plants developed 

 an abundance of nodules. 



The development of nodules may also be affected by other agencies. 

 Gain (1893) attempted to determine the influence of moisture on nodule 

 (development on Pisuni sativum, two varieties of Lupinus albus, and 

 Faba vulgaris. He grew the plants in a field located in a region where 

 rain was very scarce during the early part of the summer. One-half of 

 the plat planted with each legume was watered artificially, and the other 

 half was exposed to drought. Examination of the plants showed that 

 the plants watered artificially had five and one-half times as many nodules 

 as those not watered. 



Marchal (1901) determined the influence of fifteen different nutritive 

 mineral salts on nodule development on peas grown in Sachs' nutrient 



