CYANOGENETIC GLUCOSIDES 255 



variable, depending on the specific physiology of the plant, 

 the age and condition of the plant member, the conditions of 

 erowth, and so on. Wherefore no general conclusion can for 

 the time being be reached ; this, in fact, may only be possible 

 when knowledge of the sequence of metabolic events, in which 

 the glucoside is involved, in each distinctive case is gained and 

 correlated. This has been done, in part, in one instance. 

 Godwin and Bishop * have traced the relations of the glucoside 

 of cherry laurel leaves to the yellowing stage, and the respira- 

 tion phenomena of starvation. When the mature green leaf 

 is placed in the dark, the available sugars are consumed in 

 respiration, and the hexose concentration perforce falls. With 

 this fall there is a corresponding diminution in the respiration 

 rate and with this disturbance in the equilibrium, there is a 

 tendency for the glucoside to be hydrolysed. This phase is 

 comparatively slow, but the next, marked by the yellowing 

 of the leaf, is quick. In this, senescence is marked by the 

 dominance of katabolic processes : the chlorophyll is des- 

 troyed, starch is hydrolysed and the glucoside disappears. 

 The result of these hydrolytic actions is an increase in the 

 hexose content accompanied by a rise in the rate of respiration 

 which is maintained until the sugar is exhausted. The period 

 of maximum loss of glucoside coincides fairly closely in time 

 with similar maxima in the rates of yellowing and of respiration. 



The younger the leaves, the smaller is the rate of loss of 

 glucoside before yellowing and the longer is the postponement 

 of the beginning of the second phase of rapid loss. 



Godwin and Bishop draw no conclusion regarding the 

 possible role of cyanogenetic glucoside in the plant. They 

 content themselves by pointing out that the three main 

 phases in the life of a member may possibly be explained by 

 the changes in the condition of the protoplasm. 



Reactions, Microchemical and Otherwise. 

 I. The presence of cyanogenetic glucosides or of free 

 hydrocyanic acid can generally be detected by chewing a 

 small piece of the material. 



* Godwin and Bishop : " New Phyt.," 1927, 26, 295. 



