44 



HOW PLANTS GROW. 



in a Quince-leaf: 5, the blade; p, the footstalk ; and st, the stipules, looking like a 

 pair of little blades, one on each side of the stalk. But many leaves have no 

 stipules ; many have no footstalk, and then the blade sits directly on the stem (or is 

 sessUe), as in Fig. 138. Some leaves even have no blade; but this is uncommon; 

 for in foliage the blade is the essential part. There- 

 fore, in describing the shape of leaves, it is always 

 the blade that is meant, unless something is said to 

 the contrary. 



121. Leaves are either simple or compound. They 

 are simple when the blade is all of one piece ; com- 

 pound, when of more than one piece or blade. Fig. 

 128 to 132, and 133, are examples of compound leaves, 

 the latter very compound, having as many as eighty- 

 one little blades. 



122. Their Structure and Veining, Leaves are com- 

 posed of tlie same two kinds of material as stems (110), 

 namely, of wood or fibre, and of cellular tissue. The 

 woody or fibrous part makes a framework of ribs 

 and veins, which gives the leaf more strength and 

 toughness than it would otherwise have. The cellu- 

 lar tissue forms the green pulp of the leaf. This is 

 spread, as it were, over the framework, both above 



and below, and supported by it ; and the whole is protected by a transparent skin, 

 which is termed the Epidermis. 



123. Ribs. The stouter pieces or timbers of the framework are called Ribs. 

 In the leaf of the Quince (Fig. 82), Pear, Oak (Fig. 120), &c. there is only a single 

 main rib, running directly through the middle of the blade from base to point ; this 

 is called the Midrib. But in the Mallow, the Linden (Fig. 83), the Maple (Fig. 

 84), and many others, there are three, or five, or seven ribs of nearly the same size. 

 The branches of the ribs and the branchlets from them are called 



124. Veins and VcinletS. Tlie former is the general name for them ; but the finest 

 branches are particularly called Veinlets. Straight and parallel veins or fine ribs, 

 like those of Indian Corn, or of any Grass-leaf, or of the Lily of the "S'alley (Fio-. 

 3, 85), are called Nerves. This is not a sensible name, for even if in some degree 

 like the nerves of animals in shape, they are not in the least like them in use. 



