18 Development and Activities of Roots of Crop Plants. 



Manchubia Barley, Hordeum vulgare. 



The barley roots were examined the first time April 25, 20 days after the 

 seed had been drilled. The plants had shown above ground about 8 days. 

 They averaged 5 inches in height and the second leaf was just beginning to 

 unfold. In this early state of growth, however, the root system showed a 

 marked tendency to develop into two rather distinct portions. One set of 

 roots grew at once toward the subsoil, while the other ran off quite hori- 

 zontally. Of the former lot there were two or three on every plant. Quite 

 regularly one of these, not unlike the others in structure or general appear- 

 ance, took a course so vertically downward as to constantly remind one of 

 a tap-root. The others, while nearly always growing rather straight down- 

 ward, occasionally wandered off in an oblique direction to a distance of 6 to 

 9 inches from the perpendicular and finally reached a depth of 0.7 to 1.2 

 feet. Small branches had appeared on the older portions of the roots to a 

 distance sometimes as great as 4.5 inches from the base of the plant. The 

 branches did not exceed 0.5 inch in length. 



The other portion of the root system consisted of four or five roots which 

 usually took an almost horizontal course through the soil. Occasionally 

 one or two of these even curved up slightly towards the surface. Many 

 reached a length of 4 to 8 inches and ended only 3 or 4 inches below the soil 

 surface. This portion of the root system was also branched quite sparingly. 

 However, the branches occurred to within an inch of the root-tips. The roots 

 were a millimeter or less in diameter, light in color, rather elastic, and quite 

 well covered with root-hairs to within a short distance of the tip (fig. 5 a). 



The second examination was made on May 29, 54 days after planting. 

 The number of stalks per plant, including tillers, varied from 2 to 4. The 

 height ranged from 9 to 12 inches. Barley, as was true of all the small 

 cereals at the time of the second examination, had thrown out roots from two 

 distinct points, the original ones from the hypocotyl and the second group 

 from a node just below the surface of the soil. The shallower and deeper 

 portions of the system already noted were still maintained (fig. 5 b). The 

 roots composing the former extended out almost horizontally in all directions 

 from the base of the plant, or had only a slightly downward course. In 

 number they ranged from 8 to 12, were from 5 to 16 inches long, and ended 

 from 2 to 10 inches below the surface of the soil. These shallower roots 

 were profusely branched and rebranched to the second and third orders 

 with thread-like branches varying from a few millimeters to 3 or 4 inches 

 in length. The first 6 to 8 inches of soil were densely filled with these hori- 

 zontal roots and their network of branches. 



The second type of roots penetrated deeply. Two to four occurred on 

 each plant. The depth of penetration was usually from 3.7 to 4.2 feet, 

 although some reached the 4.5-foot level. These main roots frequently took 

 a vertical course, but as often wandered obliquely from the base of the plant 

 to a distance of 8 to 10 inches and then ran irregularly downward. These 

 roots were profusely branched within the first 3 feet of soil; sometimes as 

 many as 20 branches occurred on a single inch. The last 6 to 8 inches were 

 not branched. The old roots near the base of the plant were hard, wiry, 

 and yellowish in color, while the new ones were crisp and white. None of 

 them, at this point, were more than 1 mm. in diameter. As a rule, the diam- 



