8 THE TREE BOOK 



as a protection to river banks. In our country 

 they plant themselves. Their long, rigid roots 

 are invaluable in binding together the loose 

 shifting soil of sand dunes and bars. Their 

 foliage decays and helps to form a soil in which 

 other trees and plants can live and thrive. 



Trees everywhere are great makers of soil. 

 You will understand this better if you dig up a 

 little soil in the forest or grove. Under the 

 loose dry leaves you will find leaves in all stages 

 of decay : lower, you will find a dark soil, called 

 leaf mold ; below this is a loam made by filter- 

 ings from the leaf mold ; and lastly the soil of 

 that particular locality. Trees, planted upon a 

 hUl-side, fertilize and irrigate the lands below 

 and protect them from winds. 



Trees are of untold value in purifying and 

 renovating the atmosphere. Trees take in the 

 deadly carbonic acid gas, which is produced in 

 immense quantities by the decay of animal and 

 vegetable matter, by the breath of animals, and 

 by all fires in which wood, gas, coal, or petrol- 

 eum is burned; and by some process, recorded 

 only in the closed book of Mother Nature 's se- 

 crets, decomposes it and gives forth pure atmos- 

 pheric air. Of course, the plants, too, aid in this 

 process of purification: but as all the plants 

 united are not equal in bulk to the trees, it is 



