28 Journal of Agricultural Research voi. xxii, No. i 



correlated mth the best development of nodules, though the curve 

 which would be produced by these figures when plotted in the manner of 

 the preceding data would not have the same shape. The largest amount 

 of notrogen is found at a higher temperature than the point at which 

 the largest dry weight of nodules was found. A rather sudden increase 

 in nitrogen at 21° C. as compared with 18° and a sudden fall at 33° as 

 compared with 30° has characterized the series obtained thus far. The 

 result of the analyses which have been made seems worth recording; 

 but whether the low nitrogen content of the plants grown at both ends 

 of the series is wholly due to the small nodules found on these plants, 

 and whether the high nitrogen content of plants in the center of the series 

 is due to large and presumably efficient nodules, likely as this connection 

 appears, remains to be determined by more refined methods. 



DISCUSSION OF FACTORS THAT MAY HAVE HAD AN INFLUENCE UPON 



THE DATA GIVEN 



CONCENTRATION OF NITRATES IN THE SOII, 



In view of the fact already discussed, that large amounts of nitrates 

 in the soil solution decrease nodule development and even inhibit it 

 before the concentration becomes great enough to injure the plant 

 directly, it is unfortunate that the soil used in these series should have 

 had as much nitrate as was found (Table IV), even though the largest 

 amounts are far below the inhibition point. There appears to be no 

 data available in literature whereby we may know what is the maximum 

 or the more usual amount of nodular structure formed on the roots of 

 any of the legumes. Although the amount of nodular structure which 

 peas may produce may be quite different from the amount which soy- 

 beans may produce under the most favorable conditions, yet it may be 

 worth while to record here that the writers have found in one instance 

 a variety of wrinkled peas producing at the blossoming stage nodules 

 whose dry weight was 2.2 times as great as that of the entire root system 

 (average of 25 plants) ; and in individual plants the ratio of weight 

 of nodules to roots was as high as 4.5 to i. However the ratio of weight 

 of nodules to tops in these plants was 0.085 to i , a ratio not much different 

 from that found under the best experimental conditions for soybeans 

 recorded here (fig. 3, 4). 



However, the question of immediate interest here is whether or not 

 the nitrate content of the soil used in tliese series was greatly changed 

 at any of the temperatures at which it was held, and if there is any 

 evidence that this change was of sufficient size and in the right direc- 

 tion to indicate that it may have been responsible for the increased or 

 decreased nodule formation at this temperature. In order to obtain 

 information regarding the change which soil temperature maj'- have 

 produced in the series, nitrate nitrogen determinations were made by 



