Leaf casting. (A walk) 27 



a tree's natural way of getting rid of any twigs which, 

 because they are crowded or badly placed, it does not 

 want. Scotch pines go even further than this, and, as 

 they grow old, cast their branches all the way up the 

 trunk (Fig. 16). On any old pine you will see the stumps 

 left on the sides of the trunk where the branches used 

 to grow. This will happen most where trees are crowded 

 together in woods. Foresters know this and depend 

 upon this process for freeing the trunk from small use- 

 less twigs and branches, or as they call it " cleaning the 

 bole." 



All through the months of October and November 

 the falling leaves are a great trial to the owners of 

 trimly kept gardens and parks, and the gardeners are 

 kept very busy clearing them away. If you remember 

 the great heaps that they collect you will wonder what 

 becomes of the leaves in a wood, where there are no 

 gardeners. Do you know what happens to the garden 

 heaps ? They are all carefully piled together in some 

 sheltered corner where they cannot blow away and are 

 there left. If they were dry to begin with, rain and 

 dew will soon damp them, and when they have lain 

 there for a few weeks they will turn dark and soft and 

 will begin to rot away. This rotting is really a very 

 slow kind of burning, and if you put your hand into the 

 middle of the heap you will find it quite warm there. 

 As it goes on the dead leaves break up until all that is 

 left of them is a much smaller heap of dark brown 

 mould. Although it takes up much less room than the 

 leaves it contains all the rich plant food that was in 

 them. Because it holds much nourishment in a little 

 space this leaf mould is very valuable for gardening 

 and is mixed with the earth used for potting plants. 



