1 86 BIOCHEMICAL SYSTEMATICS 



others (for example, Isopyrum) roots as well as aerial parts are 

 cyanogenetic. 



More pertinent is the distribution of cyanogenetic compounds 

 within the plant kingdom. According to Dillemann, except for a few 

 isolated examples such as Bacillus pyocyaneus, and certain fungi, 

 cyanogenetic substances are restricted to advanced vascular plants: 

 about thirty species of ferns and nearly 900 species of angiosperms 

 representing ninety-five families. Families notable for the production 

 of cyanogenetic substances are the Rosaceae (150 species), Legumino- 

 sae (100), Gramineae (100), Araceae (50), Compositae (50), Euphor- 

 biaceae, Passifloraceae, Ranunculaceae, and Saxifragaceae. In some 

 families only one species is known to be cyanogenetic. Hegnauer 

 (1959b) lists about 750 species representing sixty-two families and 250 

 genera of seed plants. An indication of the frequency of cyanogenesis 

 among a broad sample of species may be obtained from results of an 

 Australian phytochemical survey (Webb 1949). Eleven cyanogenetic 

 species were found among 306 species representing sixty-seven 

 families. The positive species were scattered among several families. 



At the generic level, in some genera all species studied were 

 cyanogenetic (for example, Passiflora, Prunus, Cotoneaster, Dimor- 

 photheca) while in others some species were cyanogenetic and others 

 were not. In some genera only a single species may be cyanogenetic. 



There are several reports of the existence of physiological or 

 biochemical races within a species. Thus both cyanogenetic and 

 acyanogenetic individuals have been reported for Trifolium repens, 

 and Lotus corniculatus (Armstrong et al, 1912, 1913), Sorghum 

 vulgare (Petrie, 1913), Eucalyptus viminalis (Finnemore et al., 1938), 

 Euphorbia drummondii (Seddon, 1928) Trema aspera (Smith and 

 White, 1920), and other species. The subject of chemical races will be 

 considered in more detail in Chapter 16. 



In Lotus corniculatus a rather complex situation is encoun- 

 tered. In an intensive investigation in 1911 of populations of L. 

 corniculatus (Armstrong et al, 1912), cyanide was rarely detected. 

 However, in the following year, in which the weather was unusually 

 warm and dry, cyanide was rarely absent in the same populations of 

 these perennial plants. There were populations of the species growing 

 near each other which were markedly different in the amount of 

 cyanide present. Futhermore, the variety major was always free of the 

 cyanogen and, hkewise, free of the enzyme which, in the typical L. 

 corniculatus, was present. 



Trione (1960), who studied the cyanogen content of flax 

 seedlings in controlled environment, found that not only did the 

 HCN content increase with more light but even a diurnal variation in 



