268 Journal of Agricultural Research voi. vi, No. 7 



Accompanying these various conditions were also widely differing 

 amounts of hydrocyanic-acid glucosid. How the correlations between 

 these two may be explained will depend upon the function assigned to 

 the dhurrin in sorghum. Various uses have been attributed to glucosids 

 in plants, as (a) a protection against bacteria and other enemies by 

 means of the poison set free when some glucosids are hydrolyzed; (6) 

 a reserve food material in the plant; (c) the inactive form of a stimu- 

 lating hormone (2) set free when necessary by a glucosidase; (d) a harm- 

 less compound absorbing injurious products of metabolism; (e) an in- 

 active storage of "respiratory pigments," and other uses.^ Hydrocyanic 

 acid itself is thought by some investigators to be a necessary intermediate 

 product in protein formation (6, 8). As such, it is probably rather 

 transitory in the plant, and seldom occurs free in any appreciable 

 amount. 



A discussion of each factor which might have any bearing on the 

 cause of the variations in cyanid content, or throw any light on the 

 function of dhurrin in sorghum, follows. 



1. Humidity. — It is hard to perceive how the relative humidity might 

 have any direct bearing on the quantity of dhurrin produced. The 

 humidity affects primarily the rate of transpiration, and this in turn 

 might influence the rate of growth. The latter factor is considered in 

 the next paragraph. The interesting thing to note in the humidity 

 curves in figure 2 is the fact that the Utah curve shows a decrease dur- 

 ing a period of decreasing precipitation, which is natural, but the Kansas 

 and Minnesota curves show an increase during periods of decreasing 

 precipitation. It is possible that this very low humidity in Utah caused 

 a rate of transpiration too high for the best development of the plants, 

 and their growth was retarded accordingly. When the humidity was 

 lowest, in July and August, the plots received their two irrigations. 

 Following these the growth was more rapid. If the humidity affects 

 the amount of glucosid at all, it is by means of its effect on the nutri- 

 tion and growth of the plant. 



2. Moisture supply. — As mentioned above, there are among the 

 four stations one having very high, one with very low, and two with 

 medium rainfall. Two plots at the last-named stations were under 

 irrigation and one under dry-farming methods of cultivation. In the 

 data as a whole there is no evident correlation between the amount of 

 the glucosid and the moisture supply for the five months. Arranging 

 the stations in the order of their moisture supply, they are Kansas, Min- 

 nesota, South Dakota irrigation. South Dakota dry farming, and Utah; 

 while arranged in the order of their cyanid content they are Minnesota, 

 Utah, Kansas, and South Dakota dry farming the same, and South 

 Dakota irrigation. However, by a closer examination of the curves for 



iFor a complete discussion of the function of glucosids in plants see Armstrong, E. P., The Simple 

 Carbohydrates and the Glucosids. Ed. 2, p. 123-133. London, New York, 1912. 



