II.] ENERGY STORED BY THE PLANT 33 



burning process. In consequence, when a leaf turns 

 carbon dioxide and water into starch and oxygen, it is, 

 as it were, pushing something uphill, endowing the 

 resulting products with more energy than the original 

 material possessed, and since energy cannot be created 

 de novo any more thaJi matter can, this energy must 

 have been obtained from somewhere outside the leaf. 

 The energy required to effect the change is, in fact, 

 obtained from the light ; the green leaf simply acts as a 

 kind of transformer of the energy coming from the sun 

 in the form of light, into the stored-up energy possessed 

 by vegetable material. Stephenson was absolutely right 

 when he called coal "bottled sunlight," for the vitally 

 important feature of the coal — its power to bum and 

 give out heat, whereby it becomes a source of work — is 

 all derived from the light which fell upon those early 

 forests in which grew the vegetation that nowadays is 

 preserved as coal. The plant is not a very efficient 

 transformer of the energy of sunlight, because it only 

 picks out and utilises a very small selection from the 

 numerous rays making up the light ; according to 

 Dr Horace Brown's researches, the leaf only succeeds 

 in utilising for the manufacture of starch about xrW of 

 the energy of sunlight and -^ of ordinary diffuse day- 

 light. Small as this utilisation of the sun's energy may 

 seem to be, we must not fail to realise that in the 

 assimilation of the green leaf we see at work the only 

 great upbuilding process, by which energy is caught and 

 stored, that can be recognised as going on in the world. 

 The life of an animal is a down-grade process depend- 

 ing upon the burning up by respiration of materials 

 which have been previously built up by the plant, and 

 though the animal cannot destroy the energy that was 

 present in his food, he transforms it into low-grade 

 forms which are not longer utilisable. Decay and 



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