306 ANNUAL REPORT SMITHSONIAN INSTITUTION, 1945 



The first of these powers, limited from a practical standpoint to 

 plants which possess the green pigment chlorophyll, is the familiar 

 process of photosynthesis in which the plant transforms water obtained 

 from the soil and gaseous carbon dioxide from the air into sugar and 

 oxygen. In the course of photosynthesis, which occurs only in the 

 light, energy from the sun is stored in the product sugar and in the 

 starch, wood, oils, and fats, or other organic substances constructed 

 by living things from this sugar. The energy we obtain by burning 

 coal, lignite, peat, and petroleum was stored by the activity of plants 

 in the dim past. It represents our capital stock of usable energy and 

 once dissipated cannot be recovered. The energy in wood, sugar, plant 

 and animal oils and fats released by burning or by the metabolism 

 of living things is that part of the sun's energy stored in our time. 

 This can be regenerated within a reasonable period by the activity of 

 plants now growing. Other sources of power, water power, wind 

 power, power from the tides, are minor in comparison with the energy 

 which has been and is being stored by the photosynthesis of plants. 



The major features of this essential process were discovered and 

 elaborated by Joseph Priestley, Ingenhousz, Boussingault, and others 

 over a period of about 100 years beginning in 1771 and are taught in 

 every course in botany and biology. The details of how chlorophyll 

 works are, however, still unknown, and the basic and essential character 

 of the process is not yet a part of our national thinking. If it were, 

 the small group of men who are attempting to discover how photosyn- 

 thesis occurs — that is, how plants store the sun's rays — would receive 

 more encouragement and assistance than they do, and in the discussions 

 of the future of synthetic rubber made from petroleum we would see 

 some consideration given to the wisdom, from the long view, of using 

 petroleum in quantity to make something which can be produced from 

 the air and water by the activity of plants. 



Perhaps the significance of photosynthesis for our mechanical age 

 could be more clearly grasped if it were possible to prepare a balance 

 sheet on the world's store of available energy and the rate at which it 

 is being dissipated. This cannot be done. We can say that the coal 

 and petroleum burned annually represents a net loss of potential 

 energy, and we can also say that in time, though not in what time, we 

 will have to depend upon the energy fixed annually by plants unless 

 some other source at present not at our command, for example, atomic 

 energy, is discovered and methods for its utilization devised. 



How much energy is fixed annually by plants? xVbbot has esti- 

 mated that the energy given off by the sun amounts to the equivalent 

 of 4 X 10 23 tons of coal annually, of which the earth intercepts a small 

 fraction, the equivalent of 2X10 14 tons of coal. According to Berl, 

 plants fix each year 2.7X10 11 metric tons of carbon, which is the 



