Mar. 1901.] BOTANICAL SOCIETY OF EDINBURGH 59 



biomolecules, by successive transposition of the atoms, such 

 as has just been proved in assimilation ? The formation 

 of amyloid substances in the biomolecule would thus be 

 comparable with that of carbon dioxide ; the atoms of 

 carbon, hydrogen, and oxygen would all, or some at least, 

 be part constituent of the biomolecule before leaving it to 

 form a secretion product. Clearly, on this rendering, the 

 production of starchy substances will depend strictly on 

 the special constitution of the biomolecules and their 

 processes of assimilation. Any biomolecule may produce 

 starch, provided that by its structure and mode of develop- 

 ment it can form the atomic groups which represent starch, 

 and if these abandon the molecule after their formation. 

 These conditions not being realised the biomolecules will 

 not give origin to starch, even although from their 

 possession of chlorophyll, or of bacterio-purpurin, they can 

 utilise the carbon of the atmospheric carbon dioxide. 

 Evidently if the carbon of these ternary compounds arises 

 from the biomolecule, it must previously have been supplied 

 to the latter. It is not absolutely necessary that the 

 carbon be assimilated by the action of the chlorophyll or 

 of the bacterio-purpurin, for it might equally well have 

 been absorbed in the combined form, as it is in those non- 

 chlorophyllous organisms which none the less form starch." 

 Chlorophyll and bacterio-purpurin are of course of the 

 highest importance to those organisms which possess them, 

 but merely because they enable the organism to utilise 

 the commonest and most abundant reservoir of carbon — 

 the supply of carbon dioxide of the air, which is a secretion 

 of other organisms. 



To summarise the results of the argument — " Chloro- 

 phyll and bacterio-purpurin, in favourable conditions of 

 temperature and light, enable the biomolecule to decompose 

 carbon dioxide into its elements ; the carbon is fixed to 

 the biomolecules and becomes a constituent part of them. 

 This is the chlorophyll function. Assirailatory reactions 

 produce in the biomolecules displacement of atoms, in the 

 course of which are formed ternary atomic groups which 

 leave the molecules and constitute products of secretion 

 called starchy substances. This is the amylogenic 

 function. 



