6 Development and Activities of Roots of Crop Plants. 



north-central Kansas at Phillipsburg short-grasses intermingle with the taller 

 ones and constitute mixed prairie (Clements, 1920, 114; Weaver, 1920, 12). 

 Crops were grown at the several stations under measured environmental con- 

 ditions for the purpose of determining not only the nature of the root system, 

 but especially also its distribution and extent at various stages of growth. 

 The work was conducted under field-crop conditions and methods of tillage 

 in order that the results might faithfully portray the root relations of crops 

 as grown under usual farm practice. Moreover, extensive experiments have 

 been conducted both in the greenhouse and under field conditions to deter- 

 mine the active working-level of the roots of cereals and other crop plants as 

 regards the absorption of water and nutrients at various stages in their 

 growth. 



The method used in excavating root systems was the same as that employed 

 during the past six years. By the side of the plants to be examined a trench 

 was dug to a depth of about 5 feet and of convenient width. This affords an 

 open face into which one may dig with a hand-pick and other appropriate 

 apparatus and thus make a careful examination of the entire root system. 

 This apparently simple process, however, requires much practice, not a httle 

 patience, and wide experience with soil texture. In every case several plants 

 were examined, often 10 or more at any given stage of development, to insure 

 an adequate idea of the general root habit. Among this number it was pos- 

 sible to secure some root systems in their entirety. In cases where recon- 

 struction was necessary, this was rendered more accurate and less difficult 

 by methods of record in the field. As the work of excavation progressed, 

 the trench was deepened, so that finally the soil underlying the deepest roots 

 was undercut for several inches and carefully examined as it was removed to 

 assure certainty as to the maximum depth of the root-ends. Frequently the 

 trenches reached depths of 5 to 9 feet. 



The usual practice was followed of writing a working description of the 

 root system after several plants had been examined and then noting any 

 variation from this description as more roots were excavated. This checking 

 of the description in the field leads to a high degree of accuracy, for if any 

 point regarding the root habit remains indefinite, opportunity is offered for 

 further study. This is absolutely essential in developmental studies. 



Drawings of the root systems were made with pencil in the field on a large 

 drawing-sheet and then retraced with India ink. They were made simultane- 

 ously with the excavating of the roots and always to exact measurement. In 

 the drawing the root systems are arranged as nearly as possible in the 

 natural position in a vertical plane; that is, each root is placed in its natural 

 position with reference to the surface of the soil and a vertical fine from the 

 base of the plant. In the case of potatoes the roots were so abundant that 

 to depict all of them led to confusion, so that in the drawings of these plants 

 only one-half of the root system is shown. 



In every case it was sought to illustrate the average condition of root devel- 

 opment rather than the extreme. Although the drawings were made on a 

 large scale, the rootlets were often so abundant that it was quite impossible 

 to show the exact number as determined by average root-counts. Such 

 drawings, however, carefully executed, represent the extent, position, and 

 minute branching of the root system even more accurately than a photograph, 



