DISTRIBUTION OF PRUSSIC ACID IN THE VEGETABLE KINGDOM. 143 



ing prussic acid, the poisonous variety of Fhaseolus lunatus. This secQjid 

 series of results indicates that in this plant also prussic acid is a plastic 

 material for proteid synthesis. 



Now we may ask, Is this so for every plant and under all circum- 

 stances ? We may defend the hypothesis, but must acknowledge that we 

 have no proof for it. 



During the last twenty years many plants have been examined with 

 a view to ascertaining whether they yield prussic acid. My friend 

 Professor van Romburgh has examined over a thousand species, but only 

 a few of these gave positive results, though 0-001 per cent, of acid can 

 be detected with perfect certainty. Compared with the distribution of 

 other special plant products, e.g. saponin and cumarin, prussic acid is 

 comparatively rare. Sometimes it is absent in plants in which the litera- 

 ture states it to be present, e.g. Viola and MitcheUa. 



Those who believe that prussic acid plays an important part in proteid 

 synthesis have their answer ready, and it is worth considei-ation. The 

 plant, they say, produces the acid, but uses it immediately to produce 

 more complicated compounds. As a proof that the acid can escape 

 detection as an intermediate compound, we may refer to I'haseolus lunatus. 

 In the young leaf much free hydrocyanic acid is to be found, and in the 

 ripe seeds there is also much hydrocyanic acid, not free, but combined as 

 a glucoside, which must have been transported from the leaves along the 

 stem. But in the stem itself no prussic acid can be found. Hence it 

 must be acknowledged that the fact of this body not being found is not 

 sufficient proof that it does not play an important part in the life of the 

 plant. Nevertheless it is curious that, as a rule, we cannot find even a 

 trace of the acid with our most sensitive reagents, if at any given moment 

 we analyse the whole plant. 



It may be urged, on the other hand, that all plants do not exhibit a 

 prussic-acid stage in the proteid synthesis, and that such a phenomenon is 

 a special feature only in some plants, or in certain groups of plants. But 

 even in the Bixaceaj and the Rosacea;, hydrocyanic acid compounds are 

 limited to a few subdivisions. 



And now, if we find prussic acid in a plant, is it always of the same 

 significance ? Is it always a material for proteid formation, as it prob- 

 ably is in Pangium edule and Fhaseolus lunatus ? I do not think so. 

 The presence of the same substance in difFerent orders or genera may be a 

 proof of natural relationship showing itself in the plant by similarities in 

 its chemistry, but this need not always be the case ; the same substances 

 may arise in plants in very different ways. 



Let us pass on to another prussic-acid plant, which has been studied 

 thoroughly, i.e. the cherry laurel. Here, and in all rosaceous plants, the 

 hnkmg of the hydrocyanic acid to other substances is much stronger 'than 

 in the plants examined by Treub, and is of a difFerent type. Further, the 

 acid is not so definitely localised. In the dark the cyanogenetic com- 

 pound disappears less easily, and it even seems to be formed in the dark. 

 The role of hydrocyanic acid as the first visible assimilation product of 

 the nitrogen is not very evident in this case. The fact that in the sweet 

 almond no trace of amygdalin is present, and that only after germination 

 that body is found there, can be explained in other ways than in the 

 assumption that it takes part in proteid synthesis. Again, such a com- 

 plicated substance as lotusin more closely resembles a decomposition 

 product than an early product of phyto-synthesis. 



