196 Our Field and Forest Trees 



are made to help the leaves in their work of food- 

 making and tree-building. 



Several things must be just right before this 

 work can go on. Sunshine must fall upon the tree, 

 carbonic acid gas must be mixed in the air sur- 

 rounding it, the weather must not be too cold, and 

 water must come up from the roots into the leaves 

 and green stems. 



The first thing which the leaves make is starch. 

 On a bright summer's day a large tree can make 

 more than a pound. 



The newly made starch in leaves appears in tiny 

 grains inside the chlorophyll bodies, or close 

 beside them. It does not remain there and grow 

 into larger starch grains, but when the sunlight is 

 withdrawn it seems to melt away. 



It has been changed into glucose, and this trav- 

 els slowly along, passing through cell after cell, 

 till it reaches some growing part of the tree, where 

 it is used at once, or some resting place where it 

 is turned back into starch again, and stored away 

 to meet the needs of the future. 



In spring all the starch which the leaves make is 

 changed to glucose and used at once to " grow 

 on." But in late summer the tree puts it away. 

 The starch grains may be saved in wood or pith to 

 feed next spring's buds and shoots, or they may be 

 packed into seeds, ready to support the tree's chil- 

 dren till they grow big enough to take care of 

 themselves. 



