Robbins • The Importance of Plants 



ing 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 dissi- 

 pated 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 energ}' stored in our time. 

 This can be regenerated within a rea- 

 sonable period by the activit}' of plants 

 now growing. Other sources of power, 

 water power, wind power, power from 

 the tides, are minor in comparison with 

 the energ)' 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 Priestly, Ingenhousz, Bous- 

 singault. and others over a period of 

 about 100 years beginning in 1771 and 

 are taught in every course in botany 

 and biolog\'. The details of how chlo- 

 rophyll works are, however, still un- 

 known, 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 at- 

 tempting to discover how photosynthe- 

 sis occurs— that is, how plants store 

 the sun's rays— would receive more en- 

 couragement and assistance than they 

 do, and in the discussions of the future 

 of synthetic rubber made from petro- 

 leum we would see some consideration 

 given to the wisdom, from the long 

 view, of using petroleum in quantity' 

 to make something which can be pro- 

 duced from the air and water bv the 

 activity of plants. 



Perhaps the significance of photo- 

 synthesis for our mechanical age could 

 be more clearly grasped if it were pos- 

 sible to prepare a balance sheet on the 

 world's store of available energ\' and 

 the rate at which it is being dissipated. 

 This cannot be done. We can say that 

 the coal and petroleum burned annu- 

 ally represents a net loss of potential 

 energy, and we can also say that in 



5 



time, though not in what time, we will 

 have to depend upon the energ}' fixed 

 annually bv plants unless some other 

 source at present not at our command, 

 for example, atomic energ)', is dis- 

 covered and methods for its utilization 

 devised. 



How much energy is fixed annually 

 bv plants? Abbot has estimated that the 

 energ)' given off by the sun amounts 

 to the equivalent of 4 X 10-^ tons of 

 coal annually, of which the earth inter- 

 cepts a small fraction, the equivalent of 

 2 X 10^^ tons of coal. According to 

 Berl, plants fix each year 2.7 X 10^^ 

 metric tons of carbon, which is the 

 equivalent of somewhere near 3x10^^ 

 tons of coal. If these figures are approxi- 

 mately correct, then about 0.15 per- 

 cent of that part of the sun's energy 

 which falls on the earth is caught an- 

 nually and stored by plants. 



Riley has estimated that photosyn- 

 thetie efficiency of the world as a whole 

 to be 0.18 percent and that of the land 

 areas 0.09 percent. 



Another set of data leads to some- 

 what the same conclusion. Transeau 

 calculated that 1.6 percent of the sun's 

 energy was utilized by a field of corn in 

 Illinois during the 100 days of its grow- 

 ing season. Since for much of the rest 

 of the year a cornfield lacks vegetation 

 it would appear that something less 

 than 1 percent of the sun's energ)' an- 

 nually reaching corn land in Illinois is 

 fixed. In some parts of the Tropics and 

 other sections of the world where vege- 

 tation is active the year round this pro- 

 portion would be larger; on the other 

 hand, in the Arctic and in deserts it 

 would be much less. We may be justi- 

 fied, therefore, in assuming that the 

 annual energ)' fixation of plants ap- 

 proximates the equivalent of 3 X 10^^ 

 tons of coal. 



This astronomical figure is at first 

 sight quite comforting, particularly 

 when we learn that in energ)' value it is 

 over 200 times the coal and oil burned 



