TREES IN WINTER. 73 



that a change in the cell-contents of the leaves 

 has begun. 1 



The process of making food is carried on in 

 these leaf-cells. " They are the factories where 

 starch, or something very similar, is made." 2 The 

 raw material brought from the ground is here 

 changed into food, on which plants and animals 

 can live. Throughout the summer food has been 

 constantly made and carried from the leaves to 

 other parts of the plant, where it has been used 

 for food, or stored as a reserve for the future. 

 When this activity ceases, and the leaves fall from 

 the tree, it would be a great waste of valuable 

 material if all the food contained in their cells 

 were to be lost. Nature permits no such waste. 

 In autumn, when the life of the leaf is nearly 

 at an end, its food materials are withdrawn and 

 deposited in the stem and branches, for use in the 

 following spring. This withdrawal is preceded by 

 the breaking up of the contents of the cells. The 

 chlorophyll the green coloring-matter of the 

 leaves is decomposed ; and the products of this 

 change, together with the starch and other food 



1 Sachs, "Die Entleerung der Blatter ira Herbst." Flora. 1863. 

 p. 200. 



2 " Concerning a Few Common Plants." By G. L. Goodale. Bos- 

 ton : D. C. Heath & Co. 1886. p. 30. 



