CQ2 Journal of Agricultural Research voi. xviii. no. h 



The rainfall was relatively light but extraordinarily uniform in distri- 

 bution during the season; and, though the field soil was comparatively 

 dry most of the time, the plants did not show wilting at any stage. In 

 the boxes the plants in the "dry" sections were kept in a condition in 

 which wilting frequently occurred in the middle of the day through the 

 season. The boxes were 12 inches in width while the distance between 

 field rows was 3.3 feet. It is interesting to note, therefore, that the plants 

 in the boxes, which had slightly less than a third as much lateral soil 

 area from which to draw their moisture as was available to the plants 

 in the field, required an addition of water equal to three times the rain- 

 fall in order to attain the same development as was reached by the field 

 plants. When this condition was attained — that is, in the ' 'wet " boxes — 

 the size of the plants was almost exactly the same as that of the plants 

 in the field. 



It is seen at once (Table X) that in the boxes the water supply is the 

 chief limiting factor, for the height of the plants, the size of the stalks, 

 the production of seed, etc., are greatly affected by the quantity of the 

 water supplied. On the other hand, reduction of the water supply, even 

 to the point where almost daily wilting of the plants occurred, did not 

 change the time of flowering by a single day. Changing the water 

 supply after the flowering stage likewise produced decided effects on the 

 further development of the plants, and in the same general direction as 

 noted above, although naturally the changes are not so great as when 

 the differences in water supply are maintained throughout the active 

 period of the plant's life. As regards maturation, it was observed that 

 the plants in the wetter soil of the boxes were perhaps a week later 

 in shedding their leaves and ripening their seed pods than those in the 

 field and in the drier soil of the boxes. 



While water supply is the chief factor influencing plant development 

 in the boxes, these tests furnish a clear case of the simultaneous action 

 of two limiting factors, for the different degrees of shading likewise 

 affected the development of the plants. Quantitatively, these two 

 limiting factors are of decidedly unequal significance. Within the limits 

 covered by the tests, the effects of the differences in water supply could 

 be demonstrated in nearly all cases even if the light intensity were an 

 uncontrolled variable. On the other hand, the effects of the differ- 

 ences in light intensity would be completely masked in most instances 

 if the water supply were not rigidly controlled. This experiment illus- 

 trates the problems of soil productiveness and crop yields which con- 

 front the agronomist and clearly points to the futility of attempting to 

 deal with limiting factors of relatively small significance, such as com- 

 paratively narrow distinctions in fertilizer requirements of given soils 

 or crops or in the crop-yielding powers of different strains or varieties of 

 plants. 



