THE LIFE OF THE TREES 7 



keep their own substance sufficiently moist, and those 

 molecules that are necessary to furnish hydrogen and 

 oxygen for the making of starch. Water is needed also to 

 keep full the channels of the returning streams, but the 

 great bulk of water that the roots send up escapes by 

 evaporation through the curtained doorways of the leaves. 



Starch contains carbon, hydrogen, and oxygen, the last 

 two in the exact proportion that they bear to each other in 

 water, H-0. The carbon comes in as carbon dioxide, 

 CO-. There is no lack of this familiar gas in the air. It 

 is exhaled constantly from the lungs of every animal, from 

 chimneys, and from all decaying substances. It is diffused 

 through the air, and, entering the leaves by the stomates, 

 comes in contact with other food elements in the palisade 

 cells. 



The power that runs this starch factory is the sun. The 

 chlorophyll, or leaf green, which colors the clear protoplasm 

 of the cells, is able to absorb in daylight (and especially on 

 warm, sunny days) some of the energy of sunlight, and to 

 enable the protoplasm to use the energy thus captured to 

 the chemical breaking down of water and carbon dioxide, 

 and the reuniting of their free atoms into new and more 

 complex molecules. These are molecules of starch, C^H ^®0^ . 



The new product in soluble form makes its way into the 

 current of nutritious sap that sets back into the tree. This 

 is the one product of the factory — the source of all the 

 tree's growth — for it is the elaborated sap, the food which 

 nourishes every living cell from leaf to root tip. It builds 

 new wood layers, extends both twigs and roots, and per- 

 fects the buds for the coming year. 



Sunset puts a stop to starch making. The power is 

 turned off till another dav. The distribution of starch 



