42 



Development and Activities of Roots of Crop Plants. 



roots, laterals from 0.1 to 1 inch in length occurred at the rate of 7 to 15 per 

 inch, except near the root-ends, 0.5 to 2 inches of which were unbranched. 

 All of these laterals were of the first order only (fig. 17). The primary set 

 of roots spread laterally at an angle of about 45 degrees from the vertical; 

 the maximum lateral spread on any side of the plant did not exceed 3 inches. 

 The slow rate of development was due to adverse growth conditions. In 

 fact, during this period of 31 days, the growth was about equal to that of 

 18 days at Peru (c/. p. 31). Rotmistrov (1909 : 33) found the roots of oats, 

 wheat, and barley had an average depth of 12 inches only 7 days after the 

 appearance of the sprout. He does not record the environmental conditions 

 of the plants. In our experiment the influence of temperature is clearly 

 shown by the fact that oats planted in the same field on May 15 revealed a 

 much more advanced development of both shoot and root 15 days later than 

 had occurred in a month when the seed was sowed on March 31. Thus, the 

 very slow development of oats is clearly correlated with the unfavorable 

 conditions for growth. Throughout the month of April the weather was 

 cold and wet. Excessive cloudiness prevailed and there was a large defi- 

 ciency in sunshine. The ground was frozen for several days following April 

 2, and more or less covered with snow from April 2 to 9, while freezing tem- 

 peratures with Ught snow occurred during the latter half of the month. 



FiQ. 17.— A and B. Oats 31 daye old. 



There were only 6 clear days. The soil was wet and cold. A water-content 

 of about 22 per cent was rather evenly distributed throughout the first 5 

 feet of soil. Thermograph records from a depth of 6 inches in an adjoining 

 prairie,' gave an average temperature of about 47® F. for the last 15 days 

 of April. During this period the minimum soil temperature fell to 42" F., 

 and at no time did the maximum exceed 54° F. On May 5 the soil tempera- 

 ture at depths of 0.5 to 2 feet in the crop plats ranged from 61* to 54° F. 

 respectively. 



^ Thermographs and evaporimeters were installed in native grassland areas adjoining the crop 

 plats at all the stations except Peru, in connection with "Transplant Quadrats and Areas" (see 

 Year Book, Carnegie Institution of Washington, 1920 : 355) 



