THE CHEMICAL COMPOSITION OF CHLORELLA; EFFECT OF ENVIRONMENTAL CONDITIONS.

The purpose of the investigations here described was to determine to what extent the chemical composition of a plant can be altered by growing it under different environmental conditions. The three general processes which determine the organic composition of a plant are photosynthesis, respiration, including aerobic and anaerobic catabolism, and biosynthesis. In the present state of knowledge it is difficult to discern to what extent these three processes are interrelated. For the immediate purposes of this investigation it is, in fact, not essential to attempt to determine which of these processes may be responsible for any observed changes in composition. If decided changes in composition are observable as results of altered environmental conditions, these effects can then be further analyzed and can perhaps ultimately be ascribed to one or another of the major processes. The immediate problem was to discover which environmental conditions would, when altered, affect the organic composition of the plant, and to determine the nature and magnitude of the effect. The objective was to find environmental conditions which would materially modify the relative proportions of the three major plant constituents, carbohydrates, proteins and lipids. For such an undertaking, very little information was available as a basis for a working hypothesis to aid in the choice of environmental conditions. It was obvious from the outset, therefore, that a large number of experiments would have to be made. In an investigation requiring many analyses, the determination of the organic composition of the plants in terms of definite chemical compounds, or even of groups of compounds, would be very laborious and time consuming. Regarding all of the organic carbon of the plant as arising from the reduction of, carbon dioxide, we were more concerned with the energy level of this total organic matter than with the isolation of particular constituents. The determination of the heat of combustion of the plant material would, in a measure, satisfy this requirement; but such data would have a limited usefulness. Recourse was taken to a very simple means of determining the "degree of reduction" of the entire organic material of the plant from its elementary chemical composition. This general concept, which has been used but little in connection with problems of this nature,