CYANOGENETIC GLUCOSIDES 173 



the secretion of sugar by extrafloral nectaries, for it appears 

 that the basal cells of these structures, together with the ele- 

 ments of the adjacent tissues, are rich in glucosides. 

 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, 

 Papaveraceae, Magnoliaceae, Lauraceae, Droseraceae, Rosaceae, 

 Saxifragaceae, Leguminosae, Platanaceae, Euphorbiaceae, Com- 

 positae, etc. It will be observed from this list that some 

 Cohorts, for example Resales 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 Pangium 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 J found that as the buds 

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

 hydrocyanic compounds increases as rapidly as do the other 



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



\Loc. cit. 



:}: Verschaffelt : " Kon. Akad. Weten. Amsterdam," 1902. 



