LEAVES. 



[SECTION 7. 



name of Smilax) is peculiar and puzzling. If these blades (Fig. 167, 168) 



are really leaves, they are most anomalous in occupying the axil of another 

 leaf, reduced to a little scale. Yet they have an upper and lower face, as 

 leaves should, although they soon twist, so as to stand more or less edge- 

 wise. If they are branches which have assumed exactly the form and 

 office of leaves, they are equally extraordinary in not making any further 

 development. But in Ruscus, flowers are borne on one face, in the axil 

 of a little scale : and this would seem to settle that they are branches. In 

 Asparagus just the same things as to position are thread-shaped and 

 branch-like. 



2. LEAVES OP SPECIAL CONFORMATION AND USB. 



165. Leaves for Storage. A leaf may at the same time serve botb 

 ordinary and special uses. Thus in those leaves of Lilies, such as the 

 common White Lily, which spring from the bulb, the upper and green part 



serves for foliage 

 and elaborates 

 nourishment, while 

 the thickened por- 

 tion or bud-scale 

 beneath serves for 

 the storage of this 

 nourishment. The 

 thread -shaped leaf 

 of the Onion ful- 

 fils the same office, 

 and the nourishing 

 matter it prepares 

 is deposited in 

 its sheathing base, 

 forming one of the 

 concentric layers of 

 the onion. When 



these layers, so thick and succulent, have given up their store to the grow- 

 ing parts within, they are left as thin and dry husks. In a Houseleek, 

 an Aloe or an Agave, the green color of the surface of the fleshy leaf indi- 

 cates that it is doing ihe work of foliage ; the deeper-seated white por- 

 tion within is the storehouse of the nourishment which the green surface 

 has elaborated. So, also, the seed-leaves or cotyledons are commonly used 

 for storage. Some, as in one of the Maples, the Pea, Horse-chestnut, 

 Oak, etc., are for nothing else. Others, as in Beech and in our common 



FIG. 169. A young Agave Americana, or Century-plant : fleshy-leaved. 



