62 



LEAVES. 



[SECTION 7. 



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



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

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

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

 wise. It thev arc branches which have assumed exactly the form and 

 office of leaves, they arc equally extraordinary in iiot 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 OF SPECIAL CONFORMATION AND USE. 



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

 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 

 v 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. "\Vhen 



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

 ing parts -within, they are left as thin amt dry husks. In a Ilouscleek, 

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

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

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

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

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

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



FIG. 169. A yomr,' A;_':ivu Aiiirru'ana. <>r Century-plant; 



