LEAVES 



217 



merely useless relics, but sometimes they are used for food 



storage, as in lily bulbs, onions, etc., which are mostly made 



up of fleshy scales. In the scaly buds, so common on shrubs 



and trees, the leaves are prevented from developing by being 



kept close together, so that they overlap. These overlapping 



bud scales are clearly 



useful as protective 



structures, and to this 



end they are generally 



firm and resistant, 



often coated with 



resin, and the inner 



ones frequently 



clothed with woolly 



hairs. 



Leaves may some- 

 times develop as ten- 

 drils, either the whole 

 leaf or some of its 

 branches becoming 

 tendrils, as in the sweet 

 pea (Fig. 183). Ten- 

 drils are peculiarly 

 sensitive to contact, 

 and the resulting cur- 

 vature grips the body 

 touched, and a suc- 

 cession of tendrils thus 

 enables a plant to 

 " climb." 



Leaves are sometimes developed as thorns, as may be ob- 

 served in the barberry (Fig. 184), or sometimes only certain 

 regions of the leaf become thorns, as in the common locust, 

 acacia, etc. 



The most singular use of leaves, however, is for catching, 



FIG. 184. Leaves of barberry developing as thorns. 



