46 UNDER THE OPEN SKY 



but much-needed supply of dissolved soil. 

 This current of crude sap runs through the 

 white wood that lies between the bark and 

 the torpid centre of the tree so inaptly 

 called the heart. Out through the branches 

 it flows and into the leaves,^-for nowhere 

 else is this sort of sap of any use to the tree. 

 In the soft tissues that fill the gaps between 

 the veins of the leaf this crude material 

 meets the gases the tree has breathed in 

 from the air through the many little mouths 

 on the under side of the leaf. Wherever a 

 plant is green and t has the sun shining on 

 it, there water and air and dissolved soil can 

 be built up into sugar and starch and such 

 like plant food. These are useful to the 

 tree because in them is stored the power of 

 the sun's rays, in such form that the plant 

 can use it for doing its own work. • This 

 material too we use for food and from it we 

 gain our energy. All the life power in the 

 world, be it in the trees of the forest, in the 

 beasts of the field, or in man himself, comes 

 from the sun and comes by the way of the 

 green tissues in the plant. As fast as this 



