BY JAMES M. PETRIE. 627 



Methods. — Cyanogenetic compounds were shown to be present in 

 all the species, by plasmolysis of the tissues with vapour of chloro- 

 form. (1) Those classified as "very strong" changed colour 

 within one minute, and yielded, in one case, over0 - 015% total 

 hydrocyanic acid. (2) Those marked as "strong" gave the 

 colour change within one hour. (3) Those which required to 

 stand 24 hours before any visible change occurred, are described 

 as "faint." 



General Results. — When portions of these grasses are placed in 

 stoppered bottles, with the test paper, but without any reagents, 

 and kept at 37° C. for 24 hours, two species only were found to 

 evolve free hydrocyanic acid, these were Cynodon incompletus, 

 and Diplachne dubia. The others only gave a positive result 

 after anaesthetising. 



Immersing about 10 gm. portions in boiling water does not 

 immediately kill the enzyme; even with 2 minutes' immersion, the 

 grass subsequently liberates hydrocyanic acid when placed in 

 chloroform vapour, but when kept immersed for 2-5 minutes the 

 enzyme is completely destroyed. All the species, when thus treated 

 for 5 minutes, and found to evolve no hydrocyanic acid with 

 chloroform vapour during 48 hours, were then mixed with emulsin, 

 and quickly showed the colour change due to hydrocyanic acid 

 evolution. The compounds were thus shown to be glucosides. 



Detailed Results of the Individual Grasses. 



Andropogon halepensis. — This grass, which is regarded by 

 Hackel as the original wild species from which the sorghums have 

 sprung, is of very wide distribution, and is now considered indi- 

 genous. The reaction of the cyanogenetic glucoside was found to be 

 maximum in January and August, i.e., in the Midsummer growth 

 and the second growth due to the late winter rains. At other times 

 throughout the year, including the flowering period, the grass gave 

 only a "faint" positive reaction. 



