Leaf casting. (A walk) 



25 



grow from each side of the leaf's stalk where it was 

 joined to the main stem. As the leaf dries up the green 

 colouring matter which gives it its bright colour and 

 is called chlorophyll breaks up and disappears, its 

 place being taken by various yellow and red substances 

 according to the kind of leaf. At last the cork has grown 

 right across the leaf stalk except just where the veins 



Fig. 15. Falling Horse-chestnut leaves. 



pass into the leaf. At this stage the leaf is seen to be 

 hanging on by a few threads only. Then the cork layer 

 joins right across the middle and the leaf drops off. In 

 this way the wound on the stem is never exposed to the 

 cold air as would happen if you tore a leaf off before 

 it was ready to fall. Of course leaves are not always 

 allowed to hang peacefully on the boughs until they 



