1896 NOTES AND COMMENTS. 151 



In the stem and roots it occurs chiefly in the phloem, while in the 

 leaf it occurs in most of the parenchyma cells, but also in certain 

 specialised cells of the epidermis. To these last Dr. Treub assigns 

 the formation of the acid. By various experiments he showed con- 

 clusively that it is transported through the phloem. For its appearance 

 in the leaves he found certain conditions necessary. He could not 

 prove that the presence of carbo-hydrates was required, but in the 

 absence of light and carbon dioxide the acid rapidly disappeared from 

 the leaf. It would appear, then, that the carbon and hydrogen of 

 hydrocyanic acid comes from assimilated carbo-hydrate, while the 

 nitrogen must be obtained from material absorbed by the roots. 



In accordance with this supposition, Dr. Treub found that 

 interference with the supply of water tended to prevent the 

 appearance of hydrocyanic acid in the leaf; thus, if the vascular 

 bundles of certain lobes only of a leaf be cut, these lobes continue to 

 grow, but much less of the acid appears in them than in the uninjured 

 lobes. The connection between water-supply and the presence of 

 hydrocyanic acid is also borne out by another very interesting 

 observation ; it was found that the lowest leaf on the plant was 

 entirely or almost entirely free from hydrocyanic acid ; but, on 

 removal of all the upper leaves of the plant, hydrocyanic acid soon 

 appeared in the lowest leaf, the reason being, as Dr. Treub believes, 

 that this leaf has now the whole water-supply to draw upon, and so is 

 no longer starved for want of nitrogen salts. 



From a study of the conditions for the appearance of hydrocyanic 

 acid in the leaves, Dr. Treub concludes that in Pangmni edule, at least, 

 " hydrocyanic acid is the first recognisable product of nitrogen 

 assimilation." He believes that the carbo-hydrate formed in 

 ordinary assimilation is combined with nitric acid (set free by the 

 vegetable acids from the nitrates absorbed by the soil) to form hydro- 

 cyanic acid, and that this, by further anabolic change is converted 

 in:o proteid. 



These new and suggestive observations will no doubt lead to 

 further work from which certain conclusions may come. x\s yet 

 Dr. Treub cannot be said to have given direct evidence that carbo- 

 hydrates and nitrogen salts are necessary for the formation of 

 hydrocyanic acid ; nor for his important inference that the acid is the 

 first recognisable product of the assimilation of nitrogen. Hydro- 

 cyanic acid might equally, so far as we know, be a product of the 

 decomposition of some more complex organic body. 



Botanical Drawings. 



An interesting series of coloured drawings of plants is on view 

 at South Kensington, in the Botanical Department of the British 

 IMuseum. The largest amount of space is justly devoted to the 

 beautiful and yet botanically accurate sketches of the brothers Bauer. 



