THE LEAF 67 



a thin expansion. This is true in by far the greater 

 number of plants, but many plants, especially those which 

 live in very dry places or near the sea, have leaves which 

 are either thick and fleshy, as in the house-leek, or very 

 small, as in the heather and furze. We have also seen 

 already, when examining iris, artichoke and crocus stems, 

 that leaves are not always green. Other examples of the 

 various characters which leaves can assume will be met 



with later. 



Uses of Leaves. 



Leaves are necessary for the health and growth of 

 most plants, as in them are carried on the processes of 

 breathing and the manufacture of food-material. The 

 consideration of these processes is, however, best deferred 

 until we have made ourselves acquainted with the struc- 

 ture of leaves. We will therefore first deal with their 

 other less important uses. 



The young leaves of most plants are very delicate 

 and easily damaged by exposure to the sun, wind, and 

 frost. It is common to find these young leaves protected 

 by being enclosed by the older ones, as may be seen in 

 the leaf-buds of the lilac and privet, and very strikingly 

 in cabbages and lettuces. In the docks the young leaves 

 are rolled up within the next older leaf, and specially 

 protected from drying up by being bathed in a sticky 

 liquid. The school garden will readily furnish numerous 

 other interesting cases. In the common red clover the 

 stipules protect the young leaves. In many plants for 

 instance, the pear, apple, and beech the stipules are 

 small, and look at first sight mere useless structures. 

 Examination of the buds of these plants shows that this 



