Investigations at Peru, Nebraska. 



27 



The potato was examined only twice. The first examination was made 

 May 31, 56 days after planting. The tops were 9 to 12 inches high. At this 

 time the root system was almost entirely near the surface. As many as 55 

 roots took their origin from the base of a single plant and ran off practically 

 parallel to the surface of the soil. They varied from a few inches to 2.2 feet 

 in length. None penetrated deeper than 1.5 feet and with few exceptions 

 were throughout their length within the first 8 inches of soil. The earth about 

 the plants was so thoroughly filled with these roots that it was found impos- 

 sible to represent all of them in one plane. Consequently the drawing 

 (fig. 10) shows but one-half of the entire root system. 



Some of the roots were confined to the first 2 inches of soil. As is shown 

 in figure 10, a number of the deeper roots had a tendency to turn quite ab- 

 ruptly downward. A dry period of short duration occurred at this time, and 



Fio. 10. — One-half of root system of a potato plant 56 days old. 



it was uncertain whether this downward turn was normal or whether it was 

 a response to low water-content of the surface soil. The dry weather may 

 have had some influence, but subsequent investigation indicated conclusively 

 that this habit of growth is normal. The main roots were densely covered 

 with thread-hke branches from a few millimeters to 3 or 4 inches in length. 

 So numerous were these capillary branches that the soil to the very surface 

 was thoroughly penetrated by them. Several young potatoes from 0.3 to 

 2 cm. in diameter had formed. 



This period, excepting the last part of May, had been rather unfavorable 

 for growth, because of cool weather. The soil-temperature to a depth of 

 2 feet averaged but 55. IT. This was due in part to the high water-content 

 of the soil resulting from the heavy April precipitation. At no time, within 



