CYANOGENETIC GLUCOSIDES 1 77 



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 

 mid-day. 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. 

 In some examples of seeds which contain little or no hydro- 

 cyanic acid there may be a marked increase on germination, 

 thus in the flax, Dunstan and Henry* found that the seeds 

 contained -008 per cent of the acid, whereas in the seedlings 

 135 per cent obtained ; the same increase also occurs in the 

 sweet almond. 



These authors also point out that the percentage of hydro- 

 cyanic acid in Linum, Sorghum, Lotus arabicus and Zea Mais 

 gradually increases to a maximum and then decreases, some- 

 times 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 

 been ascertained. In this connexion attention may be drawn 

 to observations of Greshoff,f who states that the absence of 

 hydrocyanic acid does not necessarily indicate the absence of 

 a cyanogenetic glucoside. If the glucoside produced be very 

 small in amount, as in the case of Xerantkemum, the hydro- 



* 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, 374 ; 1903, ?2, 285. 



tGreshoff: "British Assoc. Rep., York," 1906, 138; " Kew Bull.," 1909, 



397. 



