324 Journal of Agricultural Research voi. vi, No. 9 



The dry weight of the stem and leaves was 9.6 times the weight of the 

 roots in 1914, and 8 times their weight in 1915. In 1914 the dry weight 

 of the grain, stem, and leaves of Blackhull kafir was 15 times that of the 

 roots, while the ratio of the dry weight of the stem and leaves to the dry 

 weight of the roots was as 10.9 to i. The average ratio of the weight of 

 all the aerial parts to the root weight in 191 5 was as 14.9 to i, while the 

 weight of the stem and leaves v\^as lo.i times that of the roots. In 1914 

 root systems of corn were obtained from 4 cans and from 10 cans in 191 5. 

 The average ratio of the weight of the stem and leaves to the weight of 

 the roots was 9.6 in 1914 and 7.8 in 1915. The roots of Dwarf Blackhull 

 kafir were isolated from five cans in 191 5. The weight of all the aerial 

 parts was 15.7 times that of the roots, while the ratio of the weight of 

 the stem and leaves to the weight of the roots was 8.9 to i. 



For the purpose of comparison the results obtained by various investi- 

 gators for the relative weights of the tops and roots of plants are given 

 here. It must be borne in mind, however, that the relative weights of 

 the roots and aerial portions of plants vary according to the conditions 

 under which they are grown. It has been shown (4, 8, 12) that, among 

 other factors, the soil-moisture content and the amount of available plant 

 nutrients are important in determining the ratio of the weight of the 

 tops of plants to their root weight. Hellriegel (3) found the ratio of the 

 aerial portions of mature barley and oat plants to the w^eight of their 

 roots to be 1 1.6 to I, and 6.6 to i, respectively. Schulze (7) reports the 

 ratio of the weight of the aerial portions to the weight of the roots to be 

 10.8, 13.5, and 1 1. 1, respectively, for mature wheat, barley, and oat 

 plants. King (5) found the weight of the aerial part of mature com to 

 be 7 times that of the root weight, while Kiesselbach (4) found the ratio 

 of the weight of the tops to the root weight to be 8.5 for com plants 

 grown in a soil with a water content of 98 per cent and 5.2 for plants 

 growing in a soil with a water content of 20 per cent. 



SOII^-MOISTUR^ CONTENT AND THB DEPTH OF ROOT PENETRATION 



In order to be able more exactly to define the conditions under which 

 the plants used for root examinations were grown, soil samples for 

 moisture determinations were taken at intervals of from 10 to 14 days 

 from the plots upon which the corn, standard kafir, and Dwarf milo 

 grew. Since the moisture content of the soil was determined a few days 

 before or a few days after the isolation of the various root systems, it 

 was possible to compare the depth of the penetration of the roots with the 

 depth of the moisture depletion of the soil. 



The results of these observations are given in Table VII. The moisture 

 content of the soil for each foot to a depth of 10 feet is shown for several 

 periods of the two growing seasons. The depth of the root penetration 

 was determined from the root systems isolated at the various stages 



