142 REPORTS ON THE STATE OF SCIENCE. 



process, as it gradually narcotises and kills any insects which may have 

 penetrated into the flower after they have performed their task of bring- 

 ing about self-fertilisation. 



The estimation of the amount of prussic acid yielded by plants is also 

 a matter of importance. In my own work I have followed the plan of 

 crushing the plant under water and then macerating it without acid in a 

 moderate quantity of water to allow the enzyme to break up the whole 

 of the cyanogenetic glucoside. Even when dealing with very small quan- 

 tities of acid I usually precipitate it at once as cyanide of silver, which, 

 after having being weighed, can still be converted into Prussian blue, I 

 may remark here that sometimes in the investigation of plants which 

 contain but a small quantity of an amygdalin-like glucoside only benz- 

 aldehyde is found in the distillate, the hydrocyanic acid being either 

 consumed by the plant or escaping into the air. Thus in Xeranthemuni 

 I found benzaldehyde repeatedly, but only once hydrocyanic acid. 

 Similarly in some plants, e.g. Gymnema, the quantity of enzyme present 

 is insufiicient to hydi'olyse the glucoside ; in that case emulsin should be 

 added in the form of sweet-almond emulsion. Treub has shown that in 

 these researches the micro- chemiciil method of studying the localisation 

 of prussic acid in the plant is of great value. I will give here the modus 

 operandi, proposed by me in 18S9. Place a freshly cut section, not too 

 thin and containing at least one layer of intact cells, in a 5-per-cent. 

 alcoholic potash solution, then transfer it after 1 5 to 90 seconds to a warm 

 (60° C.) ferrous-ferric solution (2-5 per cent, ferrous siilphate and 1 per cent, 

 ferric chloride) and leave it there for ten minutes, and Anally place it for 

 from five to fifteen minutes in dilute hydrochloric acid (one part of 

 concentrated acid and six parts of water). A section so prepared shows 

 minute agglomerations of Prussian blue wherever prussic acid occurred 

 in the original thin section. In order to follow the distribution in 

 whole leaves these may be uniformly pricked by means of a brush of 

 thin steel needles arranged in rows and then subjected to the reagents 

 mentioned above. Even hard and leathery leaves when pricked in this 

 way receive regularly distributed small holes, through which the reagents 

 can penetrate. 



As regards the physiological role of prussic acid in plants there is yet 

 no consensus of opinion. 



Treub regards the hydrocyanic acid in Panynim edule as the first 

 product of nitrogen assimilation in the formation of albuminoid matter. 

 Treub has considerable experience of plant physiology and anatomy, and 

 has built up his theory on experimental results obtained with living 

 Pangium plants at Buitenzorg, so that it cannot be refuted by mere discus- 

 sion. Prussic acid is abundant in the growing parts of this plant ; in 

 young foliage there occurs 03 per cent. HON. I estimated the total 

 amount in a single Pangium tree at 350 grams. 



This remarkable abundance of the acid and the fact that it appeai-s 

 to be produced in special cells of great chemical activity, as is proved by 

 the simultaneous occurrence iji them of prussic acid, proteid matter, and 

 calcium oxalate, and the evid^rit influence of sunlight on its formation, 

 the dependence of this formation on the presence of sugar and nitrates in 

 the green leaves in which cyanogenesis occurs, the transport of the prussic 

 acid from leaves along the phloeum to the growing parts or to the seeds 

 as a reserve material, have all been fully proved by Treub's investigation. 

 Similarly he studied for some years the physiology of another plant yield- 



