May IS, 1916 Hydrocyanic-acid Content of Sorghum 269 



each plot, the following examples tending to show that high water sup- 

 ply is often accompanied by a low cyanid content are discernible: (i) 

 The normal hydrocyanic-acid curve for sorghum during the first two- 

 thirds of its growth is a smooth curve, with a steady decrease in the acid. 

 The Utah curve is an exception to this. In this plot there was for several 

 weeks very rapid transpiration of water, owing to low humidity; hence, 

 the plants and soil were reduced nearly to the minimum water require- 

 ment. Shortly after the first irrigation the hydrocyanic acid is seen to be 

 on a normal decline. Twenty days after this irrigation, however, the plots 

 had become comparatively dry again, and the hydrocyanic acid shows 

 a less decrease in variety S and an actual increase in variety N. The 

 second irrigation was followed by another decline in hydrocyanic acid. 

 By the latter part of August the need of water was once more felt, and 

 the cyanid in variety N, at least, had ceased to decrease. (2) The curve 

 for the South Dakota dry-farming plot also shows an abnormality in 

 that the last part of it has an upward turn in the case of variety N. It 

 is possible that this may be due to the smaller supply of moisture avail- 

 able at this time. (3) In the two South Dakota plots, both received the 

 same amount of rain; one was irrigated once and the other, being culti- 

 vated by dry-farming methods, had a larger reserve supply of water. 

 This would apparently give them about the same amount of water 

 supply, except for the fact that the irrigation was a heavy one, and the 

 heavy rains during May, June, and July disturbed the usual dry-farming 

 condition of the soil. Assuming that the irrigated plots did have more 

 water available, it will be seen that they also contained a less amount of 

 hydrocyanic acid. (4) On analyzing some sorghum plants grown in 

 pots in the greenhouse, they were found to contain no hydrocyanic acid. 

 A few weeks later some larger plants from this same group, growing in 

 drier soil, owing to lack of care in watering and to a larger demand made 

 by the plants, were found to contain some of the acid. There appears, 

 therefore, to be a relation between the supply of water and the amount 

 of dhurrin present. This may be explained on the hormone theory 

 With a liberal supply of water, other things being equal, the plant's 

 means for growth are adequate and it needs less glucosid. With a 

 decreasing water supply, hovv^ever, the plant may need the hormone 

 stimulus for growth, and more glucosid is produced. Although, as shown 

 by Briggs and Shantz (5), sorghum has a lower water requirement than 

 most cultivated plants, it is no doubt affected by changes in the supply 

 of moisture. 



3. Temperature. — No correlation has been found between the con- 

 tent of dhurrin in sorghum and variations in temperature, at least for 

 the range of temperatures which obtained during this experiment. The 

 increase in hydrocyanic acid which sometimes occurs when plants are 

 frosted may be due to disturbed enzym balance. 



