Mar. 8, 1924 
Effect of Nitrate on Prussic Acid in* Sorghum 
723 
SUMMARY 
The hydrocyanic acid was determined in sorghum plants grown in the 
greenhouse, using three Minnesota soils low in nitrogen and adding 
sodium nitrate in different amounts. The size of the plants, their color 
and prussic acid content were all affected by the amount of nitrate 
applied. 
In general, the percentage of hydrocyanic acid in the green plants, 
was in proportion to the nitrate used. The effect on the prussic acid 
content continued even beyond the point where nitrate ceased to affect 
the color and size of the plants. In the light-colored sorghum plants, 
yellow to yellowish green, the percentage of prussic acid was very low, and 
in some cases none could be detected, while in all darker colored plants 
it was readily determined, even single plants weighing only 2 gm. 
giving distinct qualitative evidence. The leaves of the darker-colored 
plants contained several times as high a percentage of prussic acid as the 
stems, and the applications of nitrate showed no distinct effect upon its 
distribution between stem and leaf. 
Sorghum gives promise of being useful as an indicator plant in studies 
of the supply of readily available nitrogen in soils. It responds readily 
not only by a more rapid growth and darker color but also by an in¬ 
creased hydrocyanic-acid content, which is highest in the young plants. 
As analysis requires only small samples; these may be had within a few 
weeks after the seed is planted. 
