84 



Development and Activities of Roots of Crop Plants. 



and night air-temperatures during this interval are shown in figure 37. In 

 general, the temperature is highest at Lincoln and lowest at Burlington. 

 The low night temperature (45° to 56° F.) is especially significant in con- 

 sidering the growth of crops. The lower relative humidity and greater 

 wind movement is indicated by the higher evaporation at Phillipsburg and 

 Burlington (fig. 38). 



On May 25, the barley at Lincoln began to head out. By the first of June 

 all of the crops were fairly well headed and had an average height of 3 feet. 

 The wheat and oats continued heading during the first week of June. The 

 crops had been blown down badly on May 8 during a heavy rainstorm, 

 but recovered more or less completely by June 1, when another storm lodged 

 the wheat and barley again. 



May June July 



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Fig. 38. — Average daily evaporation at Lincoln (solid line), 

 Phillipsburg (long broken lines), and Burling- 

 ton (short broken lines), 1921. 



At Phillipsburg the crops headed out about a week later than at Lincoln. 

 Moreover, they developed much more irregularly, the barley having an 

 average height on June 10 of about 2.7 feet, the oats 2.3 feet, while the wheat 

 was only 1.9 feet tall. The latter crop had been rather severely damaged 

 by drought; all but the upper two or three leaves were badly discolored or dead. 



At Burlington none of the cereals exceeded a foot in average height on 

 June 10, and they did not begin heading out until 10 days later. The effect 

 of a scant water-supply was shown by the many dry and dead leaf-tips, 

 this being especially marked on the first four or five leaves. It is interesting 

 to note that these shorter plants with less extensive foliage had almost as 



