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Research Bulletin No. 3 
roots observed. In other cylinders three perennial desert legumes 
were grown until they died or were near their limit of endur- 
ance; then the cylinders were opened and the moisture content 
and root distribution determined. 
In all the cylinders bearing plants, a hard crust developed 
below the surface mulch of dry soil but it seemed to have no in- 
jurious effect. The formation of such a crust is to be regarded 
as unavoidable where during a prolonged period of rainless 
weather plants with a well-developed root system and a very 
limited amount of moisture in the subsoil are transpiring a large 
amount of water. 
In their ability to exhaust the moisture of the subsoil before 
dying. Red Fife wheat, Kubanka wheat, milo. Mexican beans, and 
maize showed little difference, but in their ability to continue 
alive after first showing serious injury from drouth they ex- 
hibited marked differences. The interval between wilting and 
death in the case of the beans amounted to only a few days but 
in that of wheat and milo it often extended to many weeks. 
Where there was a well-developed root system and no remark- 
ably unfavorable conditions occurred before the death of the 
plants, the moisture content could be reduced by any of these 
plants almost to the hygroscopic coefficient. 
In experiments with perennial desert legumes the plants re- 
mained alive after the water content had fallen slightly, but 
distinctly, below the hygroscopic coefficient, even to the point at 
which all the above-mentioned annual crop plants had died. 
Under favorable conditions these legumes adjusted themselves 
to the gradually increasing dryness of the soil by dropping their 
leaves one by one, but where, with the subsoil moisture already 
reduced to near the hygroscopic coefficient, conditions causing 
an abnormally high transpiration suddenly set in. death oe- 
curred without the leaves having dropped. While the experi- 
ments furnish no evidence of any ability on the part of these 
legumes to utilize for growth the last portion of free water, 
they indicate that this portion has a very high value for the 
maintenance of life and that even some of the water below the 
hygroscopic coefficient may be available for the maintenance of 
life in these plants. 
In the portions of a semiarid subsoil where roots are well de- 
veloped the final content of free water is independent of the dis- 
tance from the surface, except where the stored water is much in 
excess of the amount required for the complete maturity of the 
plant. 
When the portion of the subsoil in immediate contact with the 
roots contains only a comparatively small amount of free water. 
