Oct. 1. 1921 Effect of Soil Temperature on Development of Nodules 23 



washed from the soil and the nodules were counted. The count obtained 

 is given in Table I. In the two later series the seeds were planted in 

 soil which had already been placed in the tanks adjusted to the tem- 

 peratures designated. The air temperature ranged from 14° to 18°. 

 The counts obtained in these series are given in Table 11. 



Table I. — Average number of nodules produced on plants 26 days old grown at a soil 

 temperature of about 20° C.for 10 days, after which mociilation was made and the tem- 

 perature of the soil was maintained as indicated 



Temperature. 



"C. 

 10 to 12 



15 



20 



25 



30 



35 



40 



Alfalfa. 



plants. 



IS 

 35 

 18 

 16 

 5 



plants. 



Red clover. 



plants. 



17 

 27 

 40 

 69 



75 

 4 



plants. 



7 

 16 



47 

 4 



75 

 6 



Soybeans. 



6 

 plants. 



46 

 61 



37 

 35 



6 

 plants. 



14 

 25 

 33 

 28 



Field peas. 



plants. 



27 

 31 

 37 

 43 

 128 



plants. 



21 

 24 



30 



60 



64 



3 



o The plants did not survive. 



Table II. — Average number of nodules produced on plants grown at the soil temperatures 



designated 



Temperature. 



Alfalfa. 



20 plants 63 

 days old. 



Red clover. 



10 plants 63 

 days old. 



Soybeans. 



6 plants 63 

 days old. 



9 plants 55 

 days old. a 



Field peas. 



S plants 32 

 days old. 



5 plants 52 

 days old. 



12 



15 



18 



21 



24 



27 



30 



33 



36 



I. 19 

 1.6 

 16. 7 

 8.0 



3-4 

 II. 6 



10.7 

 3-5 



1.8 



5-0 

 12.5 

 24. 6 

 17.4 



II- 5 

 8.9 



5-3 



o. o 

 6. I 



5-9 

 4.0 



II- 3 

 8.0 



5-8 



8.8 



13.6 



13.0 

 14.7 

 19.7 

 18.8 

 16.4 

 20.0 

 12.4 



3-6 



3-6 



8.0 



14. o 



25.8 



30.0 



4.0 



2.6 

 9.0 



27.2 

 23.8 

 13.0 



58.0 



o- The larger number of nodules on the plants 55 days old as compared with those on plants 63 days old 

 is believed to be due largely to the fact that this series of plants was grown in spring, when longer days 

 promoted a far more vigorous growth than was produced by the other plants, which were grown in winter. 



Although it will be seen at once that the data in the two tables are not 

 strictly comparable, nevertheless some temperature effects upon number 

 appear. Most conspicuous of all is the greatly increased number upon 

 peas near the upper thermal limit. But this increased number is accom- 

 panied by a more than proportionate decease in size. No plant has been 

 found to produce large nodules at 30° C. or above. Clover and alfalfa 

 tend to produce their largest numbers of nodules in the middle portion 

 of the range. Soybeans show no decided temperature effect at all, so 



