93^ Rural School Leaflet. 



The most striking difference between trees and other kinds of plants is 

 that trees grow their leaves on a crown which is lifted high in the air. Is 

 this advantageous to them? And how did they gain the power to do it? 



To answer the first question we need to know what leaves are for. 



About half the substance of dry wood, by weight, is obtained from 

 water, which is taken through the roots. Most of the other half is ob- 

 tained from air, and is taken in through the leaves. 



That anything so solid as wood should be made largely of air seems 

 a very strange thing, but it is true. A piece of charcoal is merely that 

 part of the wood which was taken from the air by the leaves, together 

 with a little mineral substance from the ground which will be left in the 

 form of ashes when the charcoal is burned. 



Trees live on soil, water, and air. The soil and water is taken in 

 through the roots. The air through the leaves. 



But leaves are also practically the stomachs of trees, because both the 

 two kinds of food are digested in the leaf. And a leaf can digest plant 

 food only when it is green. 



Leaves cannot keep green without a good supply of light. 



What difference do you observe between living and dead leaves? 

 How do you explain these differences ? 



Why do the lower branches of trees growing close together die off? 



What is the use to a tree of its trunk? What is this made of? 



It ought not to be hard now to tell why it is worth while for trees to 

 have their leaves so far from their root-mouths, in spite of the incon- 

 venience of having to lift the water so far to be digested. 



To explain how trees develop the power to grow tall, think what 

 would be the result if a quantity of seed from a single tree were planted 

 in a good-sized flower bed. Since no two individuals are exactly alike, 

 some would grow faster than others. Which would live long enough to 

 bear seed? 



Some kinds of trees throw a much denser shade than others. A hard 

 maple, for example, throws a heavier shade than an elm or aspen. This 

 is because the leaves of some kinds of trees can live and work with less 

 light than others. The power of trees to endure shade is called their 

 tolerance. An intolerant tree (that is, one which needs a great deal of 

 light) shades off its own lower branches mlich more easily than tolerant 

 kinds of trees. Hence it has a thinner crown. 



Arrange the trees with which you are familiar in a list, beginning with 

 those which endure most shade, as shown by the density of their crowns. 

 Remember that the needles of evergreen trees are their leaves, though so 

 differently shaped from the "broadleaf" trees. On which do branches 



