1903.] Cyanogenesis in Plants. 291 



The residual liquid left after extraction with ether reduced Fehling's 

 solution, and when warmed with phenylhydrazine gave a crystalline 

 precipitate of phenylglucosazone, melting at 206 



Phaseolunatinic acid is thus proved to be the dextrose ether of a 

 hydroxyisobutyric acid. 



The alkaline hydrolysis of phaseolunatin therefore takes place 

 according to the following equation : 



Dextrose ether Dextrose ether 



of acetone cyanhydrin of a-hydroxytsobutyric acid 



(phnseolunatin). (phaseolunatinic acid). 



The acid glucoside thus formed then undergoes hydrolysis by acids 

 in the following manner : 



2 6 . 



Dextrose ether of o-Hydroxytsobutyric acid. Dextrose. 



o-hydroxywobutyric acid. 



It is therefore proved that phaseolunatin is the dextrose ether of 

 acetone cyanhydrin. 



The Enzyme of Phaseolus lunatus. 



The hydrolytic enzyme of Phaseolus lunatus was isolated in the usual 

 manner by pouring an aqueous extract of the plant (containing 

 chloroform as a preservative) into excess of alcohol and collecting the 

 precipitated proteid matter. This precipitate was then re-dissolved in 

 water and re-precipitated by alcohol. Prepared in this way the 

 enzyme is an amorphous white powder almost completely soluble in 

 water; it readily hydrolyses amygdalin, salicin, and phaseolunatin. 

 The latter is also hydrolysed by the emulsin of sweet almonds, so 

 that it is probable that the enzyme of Phaseolus lunatus is emulsin, 

 although in the present state of our knowledge of the composition and 

 reactions of enzymes it is impossible to prove with certainty the 

 identity of two enzymes of different origin. 



In the two previous papers of this series,* it has been pointed out 

 that the presence of cyanogenetic glucosides in Lotus arabicus and 

 Sorghum vulgare is confined to those parts of the plant in which 

 metabolism is actively proceeding, and that the glucoside no longer 

 occurs when the plant attains maturity, and is not present in the seeds. 

 In the case of Sorghum vulgare, cultivation does not appear to diminish 

 the production of the glucoside. Phaseolus lunatus presents a different 

 group of facts since, as M. Boname has shown, the mature semi- 



* 'Phil. Trans.,' B, vol. 194, 1901, p. 515, and A, vol. 190, 1902, p. 399. 



