ROOT DEVELOPMENT OF CROP-PLANT ECADS. 127 



and as a result of frequently recurring rains the crops all came up in 

 excellent shape. The sorghum was planted on May 27. The stand 

 was thick and the plants made an excellent growth. 



A detailed discussion of the environmental conditions under which 

 the two sets of crops were grown, including soil type, water-content and 

 mechanical and chemical composition of soil, evaporating power of the 

 air, etc., is given after the description of their development. These 

 data are then correlated with the root development of the natural vege- 

 tation on the adjoining areas. 



Alfalfa (Medicago sativa). — The first examination of alfalfa roots was made 

 on June 1, 38 days after planting. In the lower plats the plants averaged 6 

 inches in height, in the upper ones they were only half so tall. The root 

 system of alfalfa is simple and easily excavated. Usually the plant sends 

 a single strong tap-root almost vertically downward, deep into the soil. The 

 tap-root gives off some branches along its course, but these are relatively 

 few and usually small. The roots in the lower field were very abundant to a 

 working level of 0.7 foot, some of the longer ones reaching depths of 1.3 to 1.6 

 feet. In the upper plats, notwithstanding the smaller above-ground parts, 

 the roots were abundant to a depth of 0.8 foot, some deeper ones penetrating to 

 1.4 to 1.7 feet. At this time the tap-roots were only 1 or 2 mm. in diameter. 

 Laterals were especially well developed in the surface 6 inches of soil, some 

 spreading rather horizontally for a distance of 2 or 3 inches or even more. 



The root development was again examined on July 8. At this time the 

 plants in the lower field were 1.1 feet in average height and those in the upper 

 plats about 0.9 foot. Alfalfa in both plats was rather badly discolored by an 

 attack of Pseudopeziza medicaginis so that at this time the plants in one of the 

 duplicate plats in each field were mown close to the ground and the forage 

 removed. In the lower plats the roots were abundant to 3 feet. The black 

 silt-loam was thoroughly moist to this depth. Some of the roots extended 

 quite through it and into the underlying wet, sticky, yellowish clay, reaching a 

 maximum depth of 3.6 feet. A typical specimen, excavated at this time, is 

 shown in figure 35. This well illustrates the dominance of the tap-root, the 

 paucity of laterals below the first foot of soil, the occurrence of nodules at con- 

 siderable depth, and the rather direct downward course. In the upland plats 

 roots and bacterial nodules were fairly abundant in the clay-loess subsoil to a 

 depth of 3.3 feet, which was the working depth of the plants. Several of the 

 longer roots extended to the 4.3-foot level. The tap-roots were fairly well 

 branched in the surface 8 to 10 inches of soil. As in the lower plats, they 

 varied from 2 to 4 mm. in diameter. Differences in number and length of 

 branches in the two areas were not pronounced, probably both being slightly 

 greater in the upland soil. 



A third examination of alfalfa roots was made on August 18. In both cases 

 the plants from which the tops were cut on July 8 were examined. In the 

 lower field these were 8 inches tall, and some were in blossom. In the upper 

 one they were only 6 inches high and not so well developed, the crop having 

 suffered from dry weather following the cutting on July 8. In the lower plats 

 the maximum root-length was 5 feet, and several plants had attained this. 

 The maximum root-depth on the upland soil, which was also reached by 

 several plants, was 4.2 feet. At this time examination was made of the 

 adjacent uncut plat, which had completely recovered from the fungus attack. 

 Here the plants were thick, about 1.1 feet high and in every way well de- 

 veloped. The roots, 116 days after the seed was sown, had reached a maximum 

 depth of 6.3 feet. These data are summarized in table 13. 



