270 Journal of Agricultural Research voi. vi. no. 7 



4. Rate of growth. — The Kansas and Utah plots present extremes 

 in rate of growth and thriftiness of the sorghum plants; and they also 

 present cases of relatively low and high hydrocyanic-acid content, 

 respectively. The cane on the Minnesota plots grew more slowly than 

 that from South Dakota, and it also contains a very much higher hydro- 

 cyanic-acid content. During the first four or five weeks on the Minne- 

 sota plots the plants grew very poorly, the weather being cold and damp. 

 The plants were yellow and uneven in height, similar to those obtained 

 from Utah. The samples from these two stations were by far the highest 

 in hydrocyanic acid. In fact, the percentage in the first Minnesota 

 sample, variety N (0.114 per cent), is the highest ever observed in the 

 authors' experience with sorghum. In the Minnesota samples of 1914 

 those grown on the poorer sandy soil were the higher in cyanid. These 

 examples, together with one furnished by Avery (3), show that some 

 significant relation may exist between poor conditions of growth and 

 high dhurrin content. In opposition to this, however, is the finding of 

 Alway and Trumbull (i) that the yellower plants in a field contained a 

 smaller amount of the acid. Balfour (4) found more in plants infested 

 with Aphis sorghi than in others not so affected. If these facts are now 

 applied to the various theories mentioned above, as to the function of 

 glucosids, some of the possibilities are as follows: (i) If this particular 

 glucosid is a food storage, it is difficult to see how it could exist in largest 

 quantities in the unhealthy, poorly nourished, slow-growing plants. (2) 

 If the constituents of the glucosid act as stimulating hormones when set 

 free by an enzym, it is possible that when conditions of growth are poor 

 more of the glucosid is produced. (3) If the glucosid is an absorber of 

 harmful products of metabolism under disturbed metabolic conditions, 

 an excess of hydrocyanic acid might be produced. Of these three the 

 authors believe the second to be the most tenable for dhurrin, according 

 to the available evidence on this question. 



5. Variety. — The most striking phenomenon in this experiment is the 

 fact that Variety vS has consistently a greater amount of hydrocyanic acid 

 than Variety N. That varietal difTerence is very important was brought 

 out also in the 1914 experiments. In fact, the authors are confident that 

 the most marked and constant differences in the hydrocyanic-acid con- 

 tent of various sorghum plants will be found to be due to variety rather 

 than to external conditions. A comparative study of the glucosid con- 

 tent of all varieties of sorghum would be interesting and valuable. 



6. Distribution in the plant. — The foregoing discussion has been 

 based on the dhurrin content of the whole plant. As is seen from Table II, 

 the distribution of the glucosid between stalk and leaves in the different 

 plots is variable. There is in every instance a more rapid decrease in the 

 stalks than in the leaves, but the comparative rate of decrease varies. 

 The Minnesota and Utah plots had the highest amount in the stalks and 

 also had the slowest growth and the thinnest stalks. The Kansas and 



