STRUCTURE OF VEGETABLES. 161 



bark, and a layer of soft wood, called alburnum, 

 Then comes the solid wood, which serves as a 

 support for the whole, and in the centre of this 

 there is, in some species of plants, a soft matter 

 called the pith. All these parts may be very 

 clearly seen in the young branch of an elder 

 tree. 



The leaves of vegetables are of many shapes, 

 and serve in a great measure for marking one spe- 

 cies from another. The upper surface of leaves 

 is in general very smooth and glossy, and of a 

 much deeper colour than the under side ; this 

 may be observed in the laurel, the willow, and 

 many other trees. 



Leaves differ, too, very much in size. In some 

 plants they are large, broad, and numerous, almost 

 hiding the branches, as in the sycamore and 

 horse-chestnut ; in others, they are small, long, and 

 narrow, as in the ash and willow. Some leaves 

 are simple, that is, having a single body; in 

 others, each leaf-stalk holds several small leaves, 

 called leaflets, as in the rose tree; such leaves are 

 named by botanists compound leaves. 



Leaves form the foliage of plants ; and are 

 found to be set upon the branches in particular 

 ways, according^ to the species. Thus, if we 

 examine the leaves of the elm or ash, we shall 

 find them arranged in one certain form, which is 

 just alike in every branch we can find. In the 

 weeping willow, the long and slender leaves are 

 pendent, or hanging, whilst the common willow, 



