POWER OF SUNSHINE 



If you walk in summer, under a tree in full leaf, it is 

 much cooler than it is in the sunshine outside. This shows 

 what happens : the sunshine has been taken up or absorbed 

 by the leaves of the tree. It does not pass through the 

 foliage, but the heat and light are stopped by the leaves. 



The light and heat which were used up by the leaves in 

 making wood, sugar, and starch come back again when that 

 wood or starch is burnt. 



So that the burning up of a bit of wood is just the 

 opposite to the formation of that wood in sunshine in a 

 living tree. The important point is that it is the sunshine 

 which is used by plants to make all these refractory bodies, 

 such as water, carbonic acid gas, and others, unite together 

 to form sugar, starch, and wood. 



As the earth revolves upon its axis, sunlight falls succes- 

 sively on every acre of land. Almost everywhere it is inter- 

 cepted by green foliage. Each leaf of every plant receives and 

 absorbs as much as it can, and, for so long as the light lasts, 

 its living particles are hard at work : water or sap is hurry- 

 ing up the stem and streaming out of the leaves as water 

 vapour. Carbonic acid gas also is hurrying into the leaves ; 

 inside these latter first sugar and then starch is being manu- 

 factured, so that the green cells become filled with starch 

 or sugar. 



So soon as the light fails, the work begins to slacken. When 

 darkness sets in, the starch changes to sugar and passes down 

 the leaf-stalk into the stem, where it is used up in growth, in 

 the formation of new wood or in supplying the developing 

 flowers or young buds. 



Next morning when the sunlight touches the plant all its 

 little living cells set to work again, and another day''s task is 

 begun. It is very difficult to understand what is going on 

 B 17 



