The Utilization of Foods 



91 



squares. The hnes in each 

 direction are still parallel. 

 This indicates that all 

 parts of the blade are 

 growing equally. 



These facts regarding 

 the growth of leaves may 

 be summarized in a some- 

 what different way. In the 

 ferns the last part of the 

 leaf to mature is the apex. 

 In parallel- veined leaves a 

 region near the base is still 

 in a growing condition 

 after the other parts are 

 mature. In net- veined 

 leaves all parts of the blade 

 mature at the same time. 



Leaves as sources of commercial products. Many plants 

 are grown or collected for the sake of their leaves. The 

 most nourishing part of forage crops like hay and alfalfa is 

 the leaves. Lettuce, celery, and Swiss chard are important 

 garden leaf crops. The leaves of the tobacco plant furnish 

 the basis of a world-wide industry. The conductive bundles 

 from the leaves of certain Mexican agaves furnish the sisal 

 fiber used in the manufacture of binder twine. Manila fiber 

 is made from the bundles of the leaves of a Philippine banana. 

 The leaves of the tropical palm, rafiia, are used by gardeners 

 for tying up plants, and by others for the making of orna- 

 mental baskets. Other tropical palms furnish the fibers 

 from which Panama hats are woven. The eelgrass, which 



-v.K, Fink 

 Fig. 56. Hat pahii, Portu Rico. The leaves 

 are split into strips and are used in weaving 



hats. 



