Exercise IX 



FIBERS 



I. Introduction.— In the strict sense, the term "fiber" shonld 

 be applied only to certain prosenchymatons cells found in the 

 inner tissues or tissue systems of the plant body. Cells of this 

 type are not to be confused with the so-called cotton "fibers" 

 which morphologically represent epidermal hairs of the seed 

 coat (ef. Anderson and Kerr, 1938). The term "fiber" is em- 

 ployed in the present book in the above restricted anatomical 



sense. 



Fibers are the most important type of mechanical cell which 

 occur in higher plants where their great tensile strength, flexi- 

 bility and elasticity serve to enable plant organs successfully to 

 withstand a variety of strains and tensions resulting from the 

 action of gravity, wind. etc. (Cf. Haberlandt, pp. 161-164.) From 

 a commercial standpoint, many plants are cultivated largely or 

 exclusively for the fibers which they produce. Among the more 

 prominent of such textile plants may be mentioned Agave sp., 

 the source of "Sisal Hemp," Musa textilis from which "Manila 

 Hemp" is derived, Cannabis sativa or the "true" hemp plant, 

 and Limnn usitatissimnni which furnishes the commercial flax 

 from which linen is derived. According to Hayward (p. 371), 

 "there is evidence that flax was grown during the Stone Age" 

 and that the annual form of Linum usitatissimum "has been 

 grown in Mesopotamia for at least 4000 years." 



Because of the considerable economic importance of fibers, a 

 very extensive literature has developed. The limited scope of 

 this book however precludes any effort to discuss in detail the 

 many involved problems of wall structure and methods of de- 

 velopment of fibers. Instead, a brief resume is given now of the 

 salient features of fibers which may serve as an introduction to 



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