president’s address. 
295 
shown to happen in the macerated cellular tissues. We, 
therefore, deduce this outstanding characteristic of an 
enzyme. An enzyme is a catalytic agent , and can induce 
chemical action in tissues without itself undergoing change. 
Before leaving this particular case of enzyme action, 
however, I should like to refer to cyanogenesis in some 
other plants, solely with a view to call attention to its 
occurrence in different phases of the plant’s life-history in 
different plants. This is a point of some physiological 
interest, and may be of economic importance. 
Lotus arabicus, an Egyptian vetch with an attractive 
bright green colour and fragrant odour, known to the Arabs 
as “Khuther,” is used by them as fodder when fully ripe, but 
is avoided as poisonous in the early stages of its growth, 
especially just before the ripening of the seeds. The plant 
has been found to contain a cyanogenetic glucoside and an 
enzyme in the early stages of growth. The enzyme persists 
after maturity, but the glucoside disappears, being hydrolised 
by the enzyme in the metabolic processes of the plant at the 
ripening period of the seed. It is a possible view that the 
“ mobilization ” of enzyme and glucoside to produce poison 
just before maturity is a measure of protection against the 
attacks of animals. 
Sorghum vulgare, the “ Great Millet,” so widely culti- 
vated in the Tropics for the sake of its valuable grain, is 
also poisonous in its young and green stages, especially at 
times of drought. This is also due to the temporary 
appearance of a cyanogenetic glucoside and its accompany- 
ing enzyme. In both cases ( Lotus and Sorghum ) the seed 
is free from glucoside. 
In the flax plant, on the other hand, the course of 
cyanogenesis is different. The seed contains a little gluco- 
side, which increases on germination, reaches a maximum at 
a very early stage in the growth of the plant (when it is 2-3 
inches high) and finally disappears altogether. 
