224 Journal of Agricultural Research voi. xii, no. 4 



the time in the growth of the seedling when permanent resistance to 

 "'attack of the organisms was established. The results obtained do not 

 ■ seem to indicate that seedling roots 18 to 20 days' old are any more 

 resistant to the attack of the organisms than are those that are younger. 

 Evidently if any reaction takes place between the nitrate and the plant 

 root it occurs during the very early stages in the development of the 

 plant. 



These results seem to point to the conclusions that the nonformation 

 of nodules in the presence of nitrates is due not to a weakening of the 

 vitality of the organism, but to some reaction between the plant root 

 and nitrate. One naturally queries whether the plant root cells are 

 made more resistant to the bacteria seeking to gain entrance there or 

 whether the naturally occurring carbohydrate food supply to be used 

 by the organisms after gaining entrance is diminished by its conversion 

 into protein material by the absorption of nitrate? Further studies 

 were not made in an endeavor to solve this question. 



INFLUENCE OF NITRATES IN SOIL ON ALFALFA NODULES AND ON THE REFORMATION 



OF NODULES 



Additional studies were made with nitrates in relation to their influ- 

 ence on nodules already formed and on the redevelopment of nodules 

 once removed from alfalfa plants. The experiments were carried out 

 in an endeavor to determine whether nitrates prevented an increase in 

 the number of nodules on plants possessing nodules and whether they 

 prevented the reformation of nodules when removed. Experiments 

 revealed clearly that removed nodules were replaced by new ones pro- 

 vided the plant was carefully replaced in the soil (soil with normal low 

 nitrate content) and the proper amount of moisture maintained. 



In these experiments i -gallon earthenware jars were used. These 

 were filled to within an inch of the top with 1,800 gm. of soil of a low 

 nitrate content. Different amounts of the nitrates to be studied were 

 added in the quantities indicated in Table XXXI. Concentrations of 

 100 and 300 mgm. of nitrate in 100 gm. of soil were also used, but the 

 transplanted alfalfa seedlings were unable to withstand such excessive 

 concentration, with the result that all died within a week or ten days 

 after transplanting. Quadruplicate pots were prepared for each con- 

 centration of nitrate. The nitrates in solution were mixed with the 

 proper amount of distilled water which, when added to the pots, brought 

 the moisture content to approximately 20 per cent. The pots were then 

 allowed to remain undisturbed for one day at room temperature to 

 allow the water containing the nitrate to become well diffused through- 

 out the soil mass. Into two pots of each set were transplanted young 

 alfalfa plants from which the nodules had been removed. The two 

 remaining pots contained transplanted alfalfa plants with the nodules 

 left on and their location noted. The plants used in this experiment 



