50 



Development and Activities of Roots of Crop Plants. 



mental conditions during the several intervals of growth have already been 

 given in the discussion of oat. It is of interest to note that wheat planted 

 May 15 was further developed after a growth period of 15 days than were the 

 31-day-old plants just described. The former were 3 or 4 inches tall, had 

 unfolded 3 leaves, and the roots were developed proportionally. But even 

 these had not made the rapid root growth recorded by Rotmistrov (1909 : 33). 



Plants 45 days old were examined on May 15. The crop had an average 

 height of 4 inches, the tallest plants exceeding this by only 0.5 inch. Some 

 plants had 2 or 3 tillers, the largest of these offshoots having 2 or 3 leaves. 

 The root development again exceeded that of oats, with a maximum depth 

 of 2.3 feet, a general working level of about 10 inches, and an extreme lateral 

 spread of 8 or 9 inches (fig. 23 a). 8 to 10 roots per plant were commonly 

 found; many new roots only 1 or 2 inches in length occurred on the plants 

 that were tillering. In the surface 6 or 8 

 inches of soil, lateral roots 1 to 3 inches 

 in length and many more shorter ones were 

 found. These had a few very fine second- 

 ary laterals only a few milhmeters long. 

 Below 10 inches the main roots became 

 ghstening white, larger in diameter, and 

 the laterals very sparse. As a whole, wheat 

 roots are somewhat finer and more thread- 

 Uke than those of oats or barley. Wheat 

 planted May 5, when 25 days old, showed 

 more advanced growth than these. It had 

 reached a height of 4 or 5 inches, was de- 

 veloping the fifth leaf, and had tillers with 

 2 or 3 leaves, A third examination of 

 wheat was made on May 29 and 31, when 

 the plants, now 60 days old, had reached 

 an average height of about 8 inches and 

 had grown 4 to 6 leaves. A few plants 

 were 12 inches tall. Nearly all had 2 or 3 

 and some 4 to 7 tillers; the largest of these 

 had 3 or 4 leaves. The roots, during the 

 15-day interval since the last examination, 



had increased to a total of 11 to 18 per plant. Many penetrated deeper than 

 before, others spread obhquely downward, and, with the increase of laterals 

 both in number and length, began to fill in the soil area already deHmited at 

 the earUer stage. The average maximum root penetration was 2.6 feet, but a 

 few roots ended 5 inches deeper. The last 8 to 12 inches of root in the very 

 moist subsoil were ghstening-white, ran vertically downward, and were not 

 only free from branches, but, hke the deep oat roots, were not well clothed with 

 root-hairs. The working depth was about 1.5 feet. The maximum lateral 

 spread was about 10 inches, although few roots spread so widely (fig. 23 b). 



Further studies were made on June 19 and 21, when the crop was in blos- 

 som. The plants averaged about 2.2 feet in height, the tallest reaching 2.8 

 feet. The number of tillers per plant varied from single-stemmed plants to 

 those with 7 or 8 tillers, but the average was about 2. 20 days of growth had 



Fig. 22. — Wheat 31 days old. 



