THE PLANT SKELETON 255 



are very coarse and stiff. These are the so-called "hard" fibers 

 secured from various Monocot leaves such as sisal and nianila 

 hemp. The fibers from sisal hemp leaves reach a length of three 

 or four feet, while those of manila hemp are usually less than a 

 foot in length. 



In Chapters 18 and 20 the economic significance of these 

 skeletal elements is considered in greater detail, showing the 

 multifarious uses to which man has put the woody tissues of trees 

 and the fibrous elements of numerous herbaceous plants. 



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