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ACCORDING to the classical and perhaps most generally accepted theory of protein synthesis in plants the amino-acids are intermediates in a process which proceeds after the pattern first outlined by Emil Fischer in the well-known polypeptide theory. On other views the amino-acids are regarded rather as the products of protein hydrolysis and as the form in which soluble nitrogen may be stored and eventually mobilized when synthesis proceeds1. Whichever of these views is held, it is a commonplace that free amino-acids are widespread in plants and they are known to exist dissolved in the cell sap, to which they contribute part of the buffering properties which titration curves reveal. This is neither the place nor the occasion to give the number of free amino-acids which have been identified in plant materials.

The conclusions which have been drawn from the results of C{sup 14}O{sub 2} fixation experiments with a variety of plants are developed in this paper. The evidence for thermochemical reduction of carbon dioxide fixation intermediates is presented and the results are interpreted from such a viewpoint.

A blue fluorescent compound, which becomes radioactive during the post-harvest conversion of nicotine-methyl-C 14 to nornicotine in leaves from a strain of cigar tobacco, has been isolated in crystalline form and identified as scopolin. Upon demethylation, all of the carbon-14, within experimental error, was found in the methoxyl group of the scopolin. This finding further supports the hypothesis that the methyl carbon of nicotine, at least to a limited extent, can enter the one-carbon metabolic pool in tobacco and serve as a precursor of the methyl groups of various metabolites.

It seems hardly necessary to repeat to an audience of this kind the importance of the process known as photosynthesis in the interaction and the interdependence of organisms and in the very existence of life as we know it. This process by which green plants are able to capture electromagnetic energy in the form of sunlight and transform it into stored chemical energy in the form of a wide variety of reduced (relative to carbon dioxide) carbon compounds provides the only major source of energy for the maintenance and propagation of all life.