CHLOROPHYLL AND ENERGY 221 



wealth — the products of chlorophyll. The quantity is important 

 because we must promote vegetation, and the problem which 

 poses itself is whether we shall have turbines or chlorophyll. 

 As for the quality, we must make the best use of the energy 

 obtained through chlorophyll, and this poses problems of 

 vegetable and even animal selection. 



Turbine or Chlorophyll? 



A quantity of water can be used either for its substance, 

 if it is made to penetrate into the hfe cycle of a plant or animal, 

 or for its mass, if it is used to drive a turbine. When a dam 

 is constructed to use the water which flows aimlessly to the 

 sea, should it serve to generate electricity, or to irrigate the 

 land?i 



One of the most essential needs of the plant is water that 

 it absorbs by its roots and gives off to the atmosphere by 

 transpiration. For the sap to rise and for the necessary sub- 

 stances to reach the leaves, the plant needs to transpire and 

 the process is so critical that there is a fairly constant ratio 

 for each species between the weight of dry matter formed and 

 the quantity of water transpired ; this is called the coefficient 

 of transpiration. 



A stem of maize builds up ^\ lb. of dry matter per day, 

 but it transpires during that time some 10 lb. of water, that 

 is, 300 lb. of water transpired for each lb. of dry substance 

 elaborated. These figures attain an average of 500 lb. for 

 barley, 550 lb. for wheat and 850 lb. for lucerne. The highest 

 figure is 1,000 lb. and the lowest 225 lb. It can therefore be 

 assumed that the average for crops is 500 lb. of water per lb. 

 of dry matter elaborated. 



If the plant had plenty of water, irrigation would be 

 unnecessary, but this is rarely the case. Too often, water is so 

 scarce that it becomes a limiting factor in growth. Under 



iJhe problem is quite topical, for France, for example, is short of 

 electricity. Hydro-electrical engineers calculate that, by making the best 

 use of rivers, a total of 8 x IQ^^ kWh. could be reached, as compared 

 with 3 X IQio kWh. today. 



