^2 SECTIONAL ADDRESSES. 



Probably the most extensive attempt to use chemical constituents for 

 botanical classification has been made by R. T. Baker and H. G. Smith, 

 in the case of the Australian genus Eucalyptus with about 200 species : 

 the essential oils from well over half of these have been examined. Baker 

 and Smith trace a relation between the venation of the mature leaves 

 and the composition of their essential oil. The genus is thus divided into 

 fairly well-marked groups, and it is possible to suggest the probable con- 

 stituents of the oil of a given species by examining the venation of the 

 leaves, and, conversely, by chemical investigation of the oil to gain a clue 

 to the species. Maiden, the botanical expert on Eucalyptus, has not 

 always agreed with the classification of the chemists, but upon occasion 

 has discovered morphological differences after a delimitation of species 

 had been proposed on chemical grounds. 



Among characteristic plant constituents perhaps most chemical labour 

 has been expended in the alkaloids, which are usually restricted to a 

 particular order, genus, or species. An increased knowledge of the various 

 amino-acids of protein, and a study of many alkaloids has in many cases 

 indicated a plausible way in which the alkaloids, particularly those con- 

 taining an isoquinoline nucleus, may arise from aromatic amino-acids, 

 by decarboxylation and ring formation from the side chain, but we are 

 still very much in the dark as to the physiological importance of alkaloids 

 to the plant. Nor is it easy to trace a connection between chemical 

 structure and botanical classification. Thus, within the same genus 

 differently constituted alkaloids may occur, or certain species may contain 

 an alkaloid and others not. Some thirty-five species of Cytisus were 

 examined by Plugge and Rauwerda ; about half contain cytisine, half 

 do not. Yet cytisine occurs in Ulex, Genista, and several other genera 

 of Leguminosae. It may even happen that in one and the same species 

 the alkaloids change according to the age of the plant. Thus Papaver 

 orientale contains during the vegetative period only thebaine, which is 

 almost entirely replaced by isothebaine after the death of the aerial parts 

 of the plant. Obviously it is very difficult under these circimistances to 

 draw conclusions as to a taxonomic relationship. The only wide generalisa- 

 tion which seems to me justified is that the large group of isoquinoline 

 alkaloids are characteristic of the rather primitive cohort, Ranales, and the 

 related order, Papaveraceae. 



The main biological interest of alkaloids is not botanical, in their 

 distribution, but pharmacological, in their action. This leads to a mention 

 of the great developments in synthetic drugs, due to organic chemistry. 

 In particular there.is great scope for the organic chemist in chemotherapy, 

 the combating of general infections of the host by synthetic drugs. The 

 production of salvarsan which had made such a great change to the treat- 

 ment of syphilis and other protozoal diseases and the subsequent intro- 

 duction of germanin (or Bayer 205) in the treatment of sleeping sickness 

 indicate great possibilities of applying organic chemistry to this particular 

 department of medicine, and constitute a link between workers in very 

 different fields. 



I have called attention to the many points of contact between organic 

 ■chemistry and biology in the past and present and if finally I am permitted 

 to draw a conclusion it would be an educational one. I hold it to be 



