,144 REPORTS ON THE STATE OF SCIENCE. 



Certainly we must be careful in generalising about the r61e of 

 prussic acid in plants. . 



The most important point to determine in the first instance is whether 

 the acid occurs free or loosely combined and circulating in the plant, or 

 combined into a definite substance to be used as a reserve material. The 

 nature of hydrocyanic acid is such as to allow of its production in difi'erent 

 physiological processes by the disruption of the albumen molecule. 



In my list of prussic-acid plants I have mentioned, so far as is known, 

 the manner in which the hydi'ocyanic acid occurs. The two most im- 

 portant forms are (1) combination with acetone, marked A ; and (2) with 

 benzaldehyde, marked B. n.B. means that we know with certainty that 

 benzaldehyde is not split off. 



I propound the question : Does a physiological difference exist 

 between those two large chemical groups, the acetonecyanohydrin and 

 the benzaldehydecyanohydrin ? On chemical grounds the acetonecyano- 

 hydrin may be regarded as a primary material for proteid synthesis. 

 Treub's plants belong to the first group, in which prussic acid is loosely 

 combined with acetone, and where the greater part of the prussic acid is 

 free and cannot be isolated in the combined form. 



With benzaldehydecyanohydrin plants, such as Pruuus and other 

 Eosaceaj, the prussic acid is associated with benzaldehyde as a stable 

 glucoside, and it is not so clear that benzaldehyde could serve as a primary 

 material for proteid formation. Nevertheless, is it not wholly impossible, 

 since the proteid molecule contains aromatic groups, and the step from 

 benzaldehydecyanohydrin to tyrosin is not an unthinkable one in phyto- 

 synthesis ? 



Many plant physiologists in Europe, with more experience with 

 Prunus or amygdalin than with the tropical Pangium, incline to the view 

 that hydrocyanic acid in these plants has nothing to do with either the 

 building-up orthe breaking-down of proteids, but that this substance is made 

 by the plant from sugar and nitrate by a special process, and serves no 

 other purpose than to defend the plants against the attacks of animals. 

 It is, above all, the incompleteness of our physiological knowledge which 

 makes decision between these theories difficult. 



In the study of this question it is important to remember the possible 

 diversity of origin of this body, and every cyanogenetic plant will be 

 requii-ed to be examined on the lines laid down by Treub. I hope my 

 paper has shown how necessary is the co-operation of botany and chemistry 

 in this work, and how much every botanical garden which aspires to be 

 something more than a mere collection of plants needs a chemical 

 laboratory. 



Allow me to conclude with the words of Professor Czapek, in his 

 recent ' Biochemistry of Plants ' (ii. 1905, p. 259), who closes his chapter on 

 this subject as follows : — 



' Die ganze Blausaurefrage bedarf eines griindlichen, umfassenden 

 Studiums, da es sich unstreitig um physiologisch wichtige Stoffwechsel- 

 vorgange handelt, und die Bildung cyanhydrin- oder nitrilartiger 

 Substanzen moglicherweise im Chemismus der Zelle eine bedeutungsvolle 

 EoUe spielt.' 



