174 GLUCOS1DES 



substances present. Treub has found that in plants growing 

 in the tropics and which contain cyanogenetic glucosides, 

 these substances disappear before leaf-fall ; in some cases this 

 depletion is quite sudden, in others the glucosides gradually 

 disappear. On the other hand in Indigofera and Sambucus 

 the glucosides are not removed before the fall of the leaves. 



Treub also states that the amount present depends on the 

 quantity of available sugar; he observed that there obtains 

 a daily variation, the maximum quantity occurring at about 

 midday. On the other hand, there is no consistent daily 

 fluctuation in Sorghum, and unhealthy plants may contain 

 more than healthy. It has also been ascertained that the 

 quantity of cyanogenetic glucosides in Pangium, Phaseolus 

 lunatus, Zea and Sorghum may be increased by the application 

 of manures rich in nitrates ; on the other hand, it must be 

 pointed out that in some cases, e.g. Phaseolus lunatus, the 

 glucoside may be eliminated from the seed by suitable methods 

 of cultivation. Also the amount varies in different varieties of 

 species, e.g. Sorghum. In some examples of seeds which con- 

 tain little or no hydrocyanic acid there may be a marked 

 increase on germination, thus in the flax, Dunstan and Henry * 

 found that the seeds contained *oo8 per cent of the acid, 

 whereas in the seedlings -135 per cent obtained; the same 

 increase also occurs in the sweet almond. Further, the 

 percentage of hydrocyanic acio^ in Linum, Sorghum, Lotus 

 arabicus and Zea Mais gradually increases to a maximum 

 and then decreases, sometimes to zero. 



The stage of development at which the maximum is reached 

 varies in the different plants ; thus, to take two extreme cases, 

 in the flax the maximum obtains when the seedlings are 

 between four and five inches high, whilst in Lotus arabicus the 

 maximum occurs at the period of flowering. 



From these observations it is clear that the actual amount 

 of the substance in question varies pretty considerably ; it may 

 be very small or relatively large, thus in the young leaves of 

 Pangium the presence of *3 per cent of hydrocyanic acid has 



* Dunstan and Henry : " Brit. Assoc. Rep., York," 1906 ; " Phil. Trans. Roy. 

 Soc., Lond.," 1901, B., 194, 515 ; " Proc. Roy, Soc. Lond.," B., 1900, 67, 224; 

 1901,68, 3745 1903, 7 2 28 5- 



