ROOT DEVELOPMENT OF CROP-PLANT ECADS. 135 



Dwarf milo, reached depths of 6 feet and had a maximum lateral spread of 

 3.7 feet. These plants were grown at Garden City, Kansas, from May 26 to 

 September 3, in rows 3.7 feet apart, in sandy loam which had been well irri- 

 gated the preceding autumn. 



Sunflower (Helianthus annuus). — Sunflowers, of the Russian variety, were 

 seeded at two different rates, one plat thick and the other thin, in both the 

 lowland and upland areas. On June 2 the plants in the lowland area had an 

 average height of 1.3 feet and a working root-depth of about 1.5 feet. The 

 maximum root penetration at this time was 2.2 feet. In the upper plats the 

 plants were 0.8 foot tall. Many roots were found at a depth of 0.9 foot, while 

 the deepest ended in the clay subsoil at the 1.3-foot level. At this time many 

 plants were removed from the plats with the thin stand, but competition 

 among plants in the thick stand was permitted to continue. On June 11 the 

 thinning was again repeated until only about 8 plants were left in the thin 

 stand on the area of 25 square feet. The crowded condition of the plants in 

 the unthinned plats at this time is shown in plate 23, a. A month later a 

 trench was dug and 3 of the sunflowers in the thin stand in the lower plats 

 were carefully excavated. The extent of the root system of these plants, 

 which were only 2.5 months old, was quite surprising. They were 6.5 to 7 feet 

 in height, had a stem diameter at the base of 1.2 to 1.5 inches, and each was 

 furnished with 35 to 40 large, active green leaves. The flower-heads were 

 fairly well formed and a week later the plants would have been in blossom. 

 Since all agreed in general root habit and extent, only one will be described. 



The major portion of one of these root systems is shown in figure 37. The 

 roots occurred in such great numbers that it was quite impossible to show 

 them all in the drawing without confusion, and for this reason the front portion 

 of the crown and swollen part of the tap-root, with their accompanying roots, 

 were removed before the penciled draft was made in the field. It may be seen 

 that the bulk of the roots lie in the surface 1.5 feet of soil. The enlarged tap- 

 root gives off so many laterals and tapers so rapidly that at a depth of 8 to 10 

 inches it is only 4 to 5 mm. in diameter and in fact no larger than some of the 

 major branches. It penetrated rather straight downward to a depth of nearly 5 

 feet. In the surface 0.5 foot of soil 28 large laterals originated. Some of these 

 ran off obliquely, at various angles with the tap, spreading rather widely, and 

 reached depths of 2 to more than 3 feet. Numerous others took a course more 

 or less parallel with the soil surface and ran off to distances of 3 or 4 feet, where 

 they ended in the surface 0.5 foot of soil, or, more rarely, turned downward. 

 One large lateral was traced to a distance of 5.5 feet from the base of the plant, 

 but at no point did any of its branches reach a greater depth than 0.7 foot. 

 Many of the large laterals had a diameter of 5 to 8 mm. They gave off few 

 or no large branches, but were thickly clothed with smaller ones. They 

 tapered very slowly and were quite coarse to their tips. The surface 0.8 foot 

 of soil, especially the first 2 feet on all sides of the plant, was so densely filled 

 with great masses of branched and rebranched roots of all sizes that they 

 formed a network. Indeed, a more profoundly developed absorbing system 

 can scarcely be imagined. Not only were roots less abundant, but the 

 branching also was poorer below the first foot. However, even in the third 

 foot, glistening white but poorly rebranched rootlets were quite abundant. 

 These were seldom more than an inch or two in length. 



On August 18 the sunflowers were again examined. At this time the 10 

 plants remaining in the upland plat of thin planting were 6.2 feet in average 

 height, the tallest reaching a height of 6.9 feet, and an average diameter of 

 24.7 mm. In contrast to this, the 7 remaining sunflowers on the lower, thinly 



