May 29, 1916 Root Systcms and Leaf A reas of Corn and Sorghum 319 



Stage I. — At this period of growth, the plants of Dwarf milo and Black- 

 hull kafir had reached a height of i foot and had four fully and four par- 

 tially unfolded leaves, while the corn plants with the same number of 

 leaves had a height of i foot 6 inches. In 191 4 the plants reached this 

 stage on June 24, four weeks from the time of planting the seed; but in 

 1915, omng to cool weather, they did not reach this stage until July 10, 

 six weeks after seeding (PL XLIII, fig. i). 



In 1 91 4 the greatest depth reached by the root system of the corn plant 

 at this stage was i foot 4 inches, while the greatest depth of the kafir and 

 milo roots was i foot 6 inches. At this time the roots of the corn ex- 

 tended horizontally to a distance of 2 feet 9 inches, while in the same 

 direction the roots of both kafir and milo extended 3 feet (PL XXXIX, 

 fig- 3)- The depth of root penetration for corn and kafir at this stage was 

 practically the same in 1915 as in 1914, but D^varf milo exceeded the 

 depth reached the previous year by 6 inches. The maximum lateral ex- 

 tent of the corn roots was the same as in 1914, but it was i foot less for 

 the kafir and milo (PL XXXIX, fig. 2, 4). 



At this time the differences exhibited by these three plants in their 

 method of rooting were very slight. The number of primary roots which 

 penetrated to a depth of a foot was between 12 and 15 for each plant, but 

 more of the first primary roots of the com took a horizontal direction 

 than did those of the kafir and milo. On this account more of the primary 

 roots of the latter penetrated to the maximum depth than did those of the 

 com plant. The secondary roots of all the plants grew both upv/ard and 

 downward from the primary roots, so that at this stage the upper foot of 

 soil was filled with a network of roots to within X inch of the surface. 



Stage II. — The root system.s at this period of growth were isolated only 

 in 1 91 4. At this time the corn plants had reached a height of 3^ feet and 

 had 8 fully and 6 partially unfolded leaves, while Blackhull kafir, with 

 approximately the same numxber of leaves, had a height of 2}4 feet. The 

 Dwarf milo plants had from 9 to 10 fully unfolded leaves, including the 

 "boot" leaf, and stood 2^ feet high. The plants reached this stage on 

 July 17, seven weeks from the time of planting (PL XLIV, fig. i). 



The greatest depth reached by the corn roots at this time v\-as 3 feet, 

 while the maximum depth for Blackhull kafir and Dwarf milo w^as 2 feet 

 6 inches and 2 feet 9 inches, respectively. The greatest lateral extent 

 reached by the roots of com and Dwarf milo at this period was 3 feet, 

 while the roots of standard kafir extended horizontally for a distance of 4 

 feet. The tendency of the first primary roots of the com to take a more 

 horizontal direction than those of the sorghums is well shown at this 

 stage (PL XXXIX, fig. i). 



It was found that the later roots of the com take the same general 

 direction as do those of Blackhull kafir and Dwarf milo, and that the 

 maximum depth of root penertation is practically the same for all three 

 plants. 



