128 ROOT DEVELOPMENT IN THE GRASSLAND FORMATION. 



The lower plats were adjacent to a field of alfalfa in which the plants were 

 2 years old. The upper part of the field had been seeded on July 5 at the rate 

 of 14 pounds per acre, the seed having been harrowed in between the rows of 

 corn. The lower portion was seeded August 6, at the rate of 17 pounds per 

 acre, after a crop of potatoes had been plowed out and the ridges harrowed down. 



A long, deep trench was dug in this field and the roots thoroughly examined 

 during the first week in June. No other plants were present and the soil was 

 occupied entirely by the roots of alfalfa. Of a large number of plants examined, 

 the tap-roots were 5 to 10 mm. in diameter. Just below the crown and to a 

 depth of 1.5 feet, the roots are well supplied with a great abundance of small 

 laterals, usually less than a millimeter in diameter. These often run off 

 parallel with the soil surface for a distance of 1 to 12 inches or even more. 



Table 13. — Development of alfalfa. 



Cut July 8. 



2 Uncut. 



Other branches run more obliquely downward, usually making wide angles 

 with the tap. They are well supplied with secondary laterals, few of which 

 are more than 2 or 3 inches in length, while many are much shorter. All of the 

 rootlets, but especially those in the surface 2 feet of soil, were abundantly 

 supplied with nodules 2 or 3 mm. long and 1 to 1.5 mm. in diameter. Indeed, 

 these occurred to the maximum depth of root penetration, about 12 feet. The 

 tap-roots tapered rather rapidly, so that at a depth of 2 feet the diameter was 

 seldom greater than 1 to 3 mm., while below 9 feet none of the roots were more 

 than a millimeter thick and usually much less. The general course of the root 

 is vertically downward. While many ended at depths of 7 to 10 feet, others 

 extended to the water-level at a depth of 12 feet, where they terminated with 

 little branching. Not infrequently the main root ran for distances of 2 to 5 

 inches in the deeper soil, giving off few or no branches. Branches more than 

 an inch in length were rare in the deeper soil and usually they were very much 

 shorter. The roots showed a marked tendency to branch only in the crevices 

 of the deeper soil, and here the branching was confined to one plane. These 

 laterals ended abruptly, and were poorly rebranched. As a whole the tap- 

 root predominates throughout and typically it branches but little, many 

 plants penetrating deeply without giving off any large laterals. One of the 

 roots, which penetrated to the water-level at 12 feet, is shown in two sections 

 in plate 16, b. Since the roots are light tan in color, they show plainly in the 

 black silt-loam. Their abundance and habit in the first 3.5 feet of soil is 

 illustrated in the bisect in plate 15, a. Here the soil was carefully removed 

 from about the roots in the face of the trench to a horizontal depth of about 4 

 inches and the roots taken in their natural position. Unfortunately, the tops, 

 which were about 1.3 feet high, were trampled down in the process of digging 

 the trench. . 



The presence of earthworm burrows in the deeper, stiff, clayey subsoil is 

 significant. These, with the countless small holes left at all depths, even to 12 



