The Tree 43 



Think of these little roots as being so many 

 small pumps; and think of the bigger roots, the 

 trunk, and the branches as pipes leading up to 

 the crown of the tree. The pumps force the 

 water and raw plant foods up from the ground 

 and into a layer of living wood \vhich covers all 

 parts of the tree and is called the '"cambium." 

 The foods, in their journey upward, are forced 

 through this and the younger bark and wood. All 

 contain many small openings or '"pores" through 

 which the food and water pass. On and on they 

 go, sometimes for more than a hundred feet, 

 until at last the crown is reached. There the 

 food goes into the branches, buds, and leaves; 

 and the leaves give off the unused water to the 

 air. 



Now all this time the leaves have been busy 

 taking in carbonic acid gas from the air. This 

 they do by breathing. A tree breathes day and 

 night through its leaves and twigs, and through 

 small holes in the bark of the trunk; but most 

 of all through its leaves. The leaves combine the 

 acid from the air with the water and minerals 

 from the soil. The raw food which the roots 

 have sent up is digested in the treetop. 



