252 SCIENCE PROGRESS. 



ance to us now could exist before the discoveries, towards 

 the end of the last century, which led to the foundation of 

 that central scientific doctrine around which the whole 

 practice of agriculture must revolve, viz., that the green 

 plant is a living focussing engine, which concentrates 

 energy, in the form of solar radiations, and packs it away 

 in its combustible substance in a latent or potential form, 

 capable of being made to do work at a later time, and in 

 another place. 



Only after a series of brilliant chemical pioneers had 

 discovered the existence and properties of oxygen, carbon, 

 hydrogen, and nitrogen, and the composition of water, car- 

 bon dioxide, and ammonia, while equally important physio- 

 logical discoveries had explained the primary functions of 

 green leaves and their relations to light and air, was it 

 possible to begin building up — laboriously and with many 

 slips at first — our present theory of nutrition (3). 



This theory can hardly be said to have obtained firm- 

 ness until Sach's splendid demonstration, about thirty-five 

 years ago (4), proved that the fulcrum on which all turns 

 is the construction of carbo-hydrates in the chlorophyll 

 apparatus of the green plant. 



Chemical and physiological theory were then in a position 

 to see more clearly than ever before that, given, on the one 

 hand, a practically limitless supply of carbon-dioxide and 

 water in the environment, and of available energy in the 

 form of solar radiations, and, on the other hand, a living 

 machine like the green plant capable of so directing this 

 energy on the carbon-dioxide and water brought together 

 in its cells that the greater part of it is stored for the time 

 being in the molecules of carbo-hydrates, resulting from 

 the decomposition of the carbon-dioxide and water, you have 

 a real source of wealth which can be theoretically calculated 

 in scientific units, and expressed in the only terms which 

 really mean access of wealth. 



Every grain of starch or sugar or other carbo-hydrate 

 thus formed is capable of liberating a perfectly definite and 

 measurable amount of energy, the amount locked up in it 

 from the sun ; and it does not matter whether this energy 



