RELATIVE WILTING COEFFICIENTS FOR DIFFERENT PLANTS. 35 



Referring to Table XII it will be seen that the corn varieties, taken 

 as a group, give a ratio which is slightly greater than unity. In other 

 words, corn appears to give a slightly higher wilting coefficient than 

 the mean of all the plants used. The several varieties of corn dif- 

 fered only slightly, the lowest ratio being given by Boone County 

 White, a variety largely grown in humid regions. It is of interest to 

 note that the Mexican and Indian varieties native to dr} r regions gave 

 no indication of being able to reduce the soil-moisture content lower 

 than other varieties. 



It will be seen that in the sorghum group also the differences 

 exhibited by the several varieties tested are small. The two varieties 

 which gave the lowest value were White durra and Red Amber, each 

 having a mean ratio of 0.94, indicating that they are capable of 

 reducing the soil-moisture content somewhat below that reached by 

 corn at the time of wilting. 



The results obtained with different varieties of the small-grain 

 crops — millet, wheat, oats, and barley — show that the influence of the 

 different varieties upon the wilting coefficient is slight, the extreme 

 range 1 for the four crops being from 0.95 to 1.03. Rye, of which 

 only one variety was tested, gave a wilting coefficient slightly lower 

 than the other grains and comparable with the sorghums. 



Of special interest are the low determinations observed in the case 

 of rice, in view of the fact that this crop is generally supplied with an 

 abundance of water. The low wilting coefficient is probably due to 

 the abundant development of fine fibrous roots, which insures a root 

 penetration through all parts of the soil. 



The different grasses tested, most of which are natives of the 

 Great Plains, gave ratios differing only slightly from one another and 

 in practical agreement with the small grains. Most of the legumes, 

 on the other hand, gave a mean wilting coefficient slightly higher 

 than the average. 



The miscellaneous plants upon which only a few determinations 

 have been made are grouped in the last part of the tables as hydro- 

 phytes, mesophytes, and xerophytes. The water plants give a mean 

 wilting coefficient slightly higher than the other groups, due to the 

 presence in this group of Isoetes, submerged plants of which were 

 taken from the water and grown in the air without being permitted 

 to develop new leaves. This plant also had a poor root distribution. 

 If we except Isoetes, the other hydrophytes give a mean wilting 

 coefficient identical with that of the mesoplrytes. The xerophytes 

 tested gave a mean ratio intermediate between the hydrophytes and 

 mesophytes. This would indicate that plants native to dry regions 

 are unable to reduce the water content of the soil to a lower point at 

 the time of wilting than is reached by other plants. 



1 Based upon all variety tests which include six or more determinations. 

 230 



