28 Development and Activities of Roots of Crop Plants. 



the layer occupied by the roots, did the available moisture fall below 11 

 per cent. Beginning with April 21, when the atmometers were installed, the 

 daily evaporation averaged but 18 c. c. per day. During the last days of May, 

 however, more favorable growth conditions ensued, and the plants passed 

 into the next period under circumstances conducive to rapid development. 



The final examination was made on July 8, 94 days after planting, when 

 growth was complete and about one-third of the leaves were dead (plate 1 b). 

 One-half of the mature root system is shown in figure 11. The root system 

 was very unlike those of the cereals, in that there was an almost entire ab- 

 sence of roots penetrating vertically downward from the base of the plant. 



Fig. 11. — One-half of root system of a mature potato plant. 



In form it was almost identical with that found in the earlier stage of its 

 development. Practically the only difference was in its extent. With a few 

 exceptions, the roots extended outward and downward until they reached 

 a distance of 0.5 to 2.1 feet from the vertical and a depth of 0.7 to 1 foot 

 from the surface. They then turned more or less abruptly downward and 

 continued their irregular course to a depth of 2 to 4.7 feet. A few roots 

 extended out almost horizontally at a depth of 2 or 3 inches to a maximum 

 distance of 15 to 20 inches, but did not turn downward at that point. All 

 these roots, including both the shallow and deep ones, were freely branched 

 throughout their course, even to their very tips, with fine white branches 



