182 



BIOCHEMICAL SYSTEMATICS 



limited, the compounds are prevalent in certain families such as the 

 Rosaceae. However, Hegnauer (1958) concluded that at present "the 

 taxonomic significance of the character of cyanogenesis is very 

 limited. Its value may be more important once the cyanogenetic com- 

 pounds of most of the known cyanophoric species are known." 

 Hegnauer has alluded to a major Hmitation of many broad surveys of 

 the distribution of cyanophoretic species. The tests generally utihzed 

 merely disclose whether prussic acid (HCN) is liberated by the 

 species. The tests do not indicate the chemical nature of the parent 

 substance. The specific type of cyanogen is known in a number of 

 cases, but in the survey work such as that of Gibbs (1954) and others, 

 only presence or absence of HCN is noted by use of emulsin and 

 sodium picrate. Even with this limitation the distribution of cyano- 

 gen is often of taxonomic interest. 



The most recent view of cyanogenetic compounds is that of 

 Dillemann (1958). Cyanogenetic substances do not include numerous 

 chemical structural analogs or modifications of the basic parent sub- 

 stance as do the alkaloids or flavonoids, and the hmited number of the 

 compounds reduces further their systematic significance. 



According to Dillemann all the cyanogenetic substances which 

 have been fully characterized consist of a sugar, a cyanhydric acid, 

 and a third substance whose nature is variable. Since the number of 

 classes of these compounds is Hmited, a rather complete chemical 

 listing is possible. The following structural formulae are obtained from 

 Dillemann, using his classification: 



True cyanogenetic heterosides. 



In the first group the nitrile (C=N) group is attached to the 

 aglycone group. 



(1) Amygdaloside occurs in many species of Rosaceae. 



CHoOH 



glucose 



(2) Vicianoside is from Vicia angustifolia (Leguminosae) 

 OH ^ ^„ H /-^ 



N=C 



c<3 



