LEAVES 



43 



-itendnis 



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As examples of the latter, may be mentioned the small, 

 scale leaves on underground stems, the scales enwrapping 

 the growing point in buds, the bracts in grass inflorescences, 

 and the petals, stamens and car- 

 pels of flowers. 



We look upon ordinary foliage 

 leaves as the most common, and 

 hence "normal," sorts of leaves. 

 We would regard scale leaves, 

 bracts, bud scales, and flower 

 parts as "modified" leaves. 



Leaves may function as (i) 

 food-making organs (foliage 

 leaves), (2) protective structures 

 (scales), (3) reproductive organs 

 (floral organs), and (4) as storage 

 organs. The fleshy leaves that 

 make up the bulb of onion are 

 good examples of leaves used for 

 storage. 



Foliage leaves are either par- 

 allel-veined or netted-veined. In 

 leaves with parallel venation, there 

 are many veins, about equal in 

 size, running parallel, and joined 

 by inconspicuous veinlets. This 

 type of venation is characteristic 

 of the leaves of grasses, sedges, 

 rushes, lilies and most all other 

 monocotyledonous plants. In 

 leaves with netted venation, which 

 is so well illustrated in leaves of apple, oak, maple, potato, 

 cabbage and other dicotyledonous plants, there are a few 



^sUpules 



Fig. 19. — A single compound 

 leaf of sweet pea. 



