LEAVES AND THEIR USES 



23s 



asparagus. Most commonly they arc protective structures. 

 But bulb scales, like those of the lilj- and the onion, serve for 

 the storage of food ; and some scale leaves (for example, 

 those of the "asparagus) contain chlorophyl and manufacture 

 a small amount of food. Scale leaves, except for their smaller 

 size, are usually similar to the blades of foliage leaves ; as a 

 rule they have no stalks. Most flowers are borne at the 

 ends of short branches, each of which grows from the axil of 

 a leaf. This leaf may be an ordinary foliage leaf. But if 

 a plant bears many flowers, and especially if the flowers are 

 close together in a cluster, the leaves from whose axils the 

 flower-bearing branches grow are likely to be smaller than 

 the ordinary foliage leaves. Small leaves, so located, are 

 called bracts. In some lilies that bear large numbers of 

 flowers, the lower flowers grow from the axils of foliage 

 leaves of about the ordinary size. The higher flowers are 

 in the axils of smaller and smaller leaves, and the uppermost 

 leaves are merely bracts. In such a case no sharp distinc- 

 tion can be riiade between foliage leaves and bracts. When 

 many flowers are borne very close together, as in the spike 

 of the mullein or the head of the red clover, each individual 

 flower grows from the axil of a very small, scale-like bract. 

 The chaffy scales of the com tassel and ear, and those of the 

 heads of wheat, oats, and other grasses, are also bracts. 



251. Thorns and Tendrils. — We have seen that some 

 thorns are branches of a special 

 form ; others, though very similar 

 in appearance, are really leaves 

 or parts of leaves, or sometimes 

 even roots. Many of the spines 

 of cactuses seem to be leaves ; 

 others are probably reduced 

 branches. The thorns of the 

 barberry (Fig. 140) are leaves; 

 some of them are simple, some 



Fig. 140. — Simple and 

 branched thorns of the com- 

 mon barberry. 



