c88 Journal of Agricultural Research voi. xviii, no. n 



dependent to a considerable extent on the relative water supply. In 

 general, however, reduction in light intensity during the period from ger- 

 mination till maturity gives results similar to those obtained in the pre- 

 ceding tests; and there is a tendency toward a reduced yield of seed, as 

 previously noted. Reducing the intensity of light during the period 

 between blossoming and final maturity, on the other hand, appears to 

 increase somewhat the yield of seed. Without exception, the plants 

 began blossoming on August 7 under all treatments as to shade and 

 differences in water supply, applied either singly or in combination. In 

 these tests it is estimated that under the heaviest shading the maximum 

 intensity of the direct sunlight reaching the plant was only 32 per cent 

 of the normal, and the average for the day could scarcely have exceeded 

 25 per cent of the normal. 



RELATION OF OTHER FACTORS OF THE ENVIRONMENT TO 



REPRODUCTION 



Having seen that under the conditions of the experiments described in 

 the previous section differences in light intensity were without effect on 

 the length of the vegetative period which preceeds flowering in soybeans, 

 it is worth while considering whether other factors of the environment, 

 especially water supply and temperature, are of significance. In study- 

 ing the relation of the water supply to ttie formation of oil in the seed, a 

 number of tests have been made with soybeans, beginning with 191 2; 

 but it will suffice to consider here only the results obtained for the years 

 1 91 6 and 191 8 with the Peking variety. In 191 6 plantings were made in 

 a series of four boxes set in the soil and provided with board covers, just 

 as has been described in the preceding section (see p. 583). Each of the 

 boxes was 12 feet long, 12 inches wide, and 12 inches deep. In one of 

 these boxes the soil was maintained in a relatively moist condition from 

 germination to final maturity, and in a second one the soil was kept 

 comparatively dry during this period. In the third box the soil moisture 

 was kept the same as that in the first box till the most active flowering 

 stage was past, after which the moisture content was reduced to that of 

 the second box. In the fourth box the soil was kept relatively dry till 

 the flowering stage was past and thereafter in a relatively moist condition. 

 A control planting receiving the actual rainfall was also made in the field. 

 The beans were planted June 2 1 , and the addition of water to the boxes 

 began July 17. The transition in the moisture relations of the third and 

 fourth boxes was begun August 1 9. The appearance of the plants in the 

 boxes in the late summer is shown in Plate 79, A. The quantities of 

 water supplied to the boxes each week, together with the rainfall for the 

 period of the tests, are given in Table X. Determinations of the mois- 

 ture content of the soil in the boxes were made at intervals through the 

 month of August. Experience has shown that in the field the soil used 

 in these tests contains i6 to 18 per cent moisture when in best condition 



