HYDROCYANIC ACID IN PLANTS 173 



CYANOGENETIC GLUCOSIDES. 



Among the more important glucosides are the cyano- 

 genetic ones, so named because on hydrolysis they yield 

 hydrocyanic acid as one of the products. 



Hydrocyanic acid is of fairly common occurrence in the 

 higher plants, and although sometimes it occurs in the free 

 state it is, in the majority of cases, combined ; the nature of 

 many of these compounds has not yet been ascertained, but it 

 is not improbable that generally they are glucosides. 



Cyanogenetic glucosides, although widely distributed, are 

 somewhat rare when compared with other glucosides such as 

 the saponins. Hydrocyanic acid has been found in a 

 few Fungi, and in certain plants of the following Natural 

 Orders of the higher plants : Polypodiaceae, Aroideae, Gra- 

 mineae, Sapindaceae, Sapotaceae, Proteaceae, Ranunculaceae, 

 Magnoliaceae, Lauraceae, Droseraceae, Rosaceae, Saxifragaceae, 

 Leguminosae, Platanaceae, Euphorbiaceae, Compositae, etc. It 

 will be observed from this list that some Cohorts, for example 

 Rosales and Ranales, stand out in having several natural 

 orders characterized by the presence of the substance in 

 question. 



In the individual plant the cyanogenetic glucosides occur 

 more especially in the leaves and buds, in the seed, and also 

 in the bark. 



In Pangiiim edule Treub * found such glucosides in the 

 phloem, pericycle, and in special cells of the leaves ; Guignard f 

 describes such compounds as occurring in the leaves of vigor- 

 ous shoots, the young bark, and in the unripe fruit of Sam- 

 bucus nigra and species of Ribes. The amount present in a 

 member is not constant ; Verschaffelt % found that as the buds 

 of Primus Padus and P. Laurocerasus open, the amount of 

 hydrocyanic compounds increases as rapidly as do the other 

 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 



* Treub: "Ann. Jard. Bot. Buitenzorg," 1907, 21, 107. 



\Loc. cit. 



JVerschaffelt : " Kon. Akad. Weten. Amsterdam," 1902. 



