2 



THE ECOLOGICAL RELATIONS OF ROOTS. 



weeds. It represents the results of the examination of approximately 

 1,150 individual plants in 8 different communities, as follows: prairies 

 of eastern Nebraska, chaparral of southeastern Nebraska, prairies of 

 southeastern Washington and adjacent Idaho, plains and sandhills of 

 Colorado, the gravel-slide, the half-gravel-slide, and forest communi- 

 ties of the Rocky Mountains of Colorado. 



The method employed in excavating root systems was to dig trenches 

 2 to 3 feet wide and 6 to 10 feet long to a depth of about 6 feet by the 

 side of the plants to be examined. This offered an open face into which 

 one might dig with a hand pick furnished with a cutting edge on one 

 end, and, after sufficient practice and acquaintance with the soil 

 texture, successfully excavate a root system almost in its entirety. 

 Of course, the trenches were deepened as work progressed and the 

 working level sometimes reached a depth of 10 or even 16 feet (plate 

 1). A total of more than 100 such pits was used. To assure absolute 

 certainty as to maximum depth, for extreme care must be used in 

 excavating root termini, the soil underlying the deepest roots was 

 usually undercut about 12 to 18 inches below the root-ends and care- 

 fully examined as it was removed. For the deepest-rooted species of 

 herbs and shrubs it was found expedient to have a longer trench with 

 two levels, one at about 7 to 9 feet and a second one about twice as 

 deep. Thus the soil could be removed from the lower to the higher 

 level as work proceeded. Indeed, in several cases where the roots 

 extended to depths of 18 or 20 feet or more (for example Rosa arkan- 

 sana or Lygodesmia juncea)j the deeper soil was removed by means of 

 a bucket attached to a rope. Considerable danger from caving was 

 experienced, especially in the sandhill soils and also in the deeper loose 

 loess soils as well. In fact, it was found inexpedient to remove the 

 entire root system in a few cases. In each community the work 

 extended over a field sufficiently large, sometimes several square 

 miles in extent, so that any local differences in soil texture, etc., were 

 eliminated. 



All of the roots examined, except as otherwise indicated, were of 

 mature perennial plants. The practice followed was to examine 

 several roots of a given species and then to write a working descrip- 

 tion of the root system. These descriptions were kept at hand, and as 

 new roots of the same species were studied, any variation from the 

 original description was carefully noted. While many of the root 

 systems, especially those of the grasses, were removed in their entirety 

 and photographed against an appropriate background, and a few 

 photographed in position, many others were drawn in place. The 

 sketching was first done with pencil on a large drawing-sheet ruled 

 to scale. Drawings were made simultaneously with the excavating of 

 the root and always to exact measurements. When entirely com- 

 pleted they were retraced with India ink. Such a drawing often repre- 



