74 FIBERS 



the subject. For students wishing cidditional technical informa- 

 tion, reference should be made to the literature cited by Hayward 

 under Caiinahis (pp. 244-245) and Linuni (pp. 409-410). 



1. Classification. Fibers, either singly or more commonly in 

 the form of strands or cylinders, are widely distributed in the 

 plant body. In stems and roots, fibers are commonly found in 

 the cortex, pericycle, phloem and xylem. In the leaves of many 

 monocotyledons (e.g., Miisa, palms, Agave, etc.), fibers are very 

 prominently developed, occurring as strands or sheaths which 

 accompany the vascular bundles; they may also appear inde- 

 pendently of the vascular strands, either as distinct bundles or 

 as massive hypodermal cylinders. (Cf. Ilaberlandt, pp. 168-184, 

 and Meeuse, 1938.) From a iopographical standpoint, two prin- 

 cipal "types" of fibers may be recognized, at least in stems and 

 roots which experience secondary growth in thickness, viz.: (1) 

 Bast or extracambial fibers, and (2) Wood fibers or intracambial 

 fibers. As Ilaberlandt (p. 155) has clearly emphasized, such a 

 distinction is quite arbitrary since bast fibers, as a class, cannot be 

 distinguished on a structural basis from wood fibers. Fames and 

 MacDaniels (p. 57) and Hay ward (p. 23) suggest that fiber types 

 should be more specifically designated according to the tissue or 

 tissue region in which they occur, e.g., cortical fibers, pericyclic 

 fibers, phloem fibers, etc. A classification of this kind, however, 

 necessarily depends upon accurate information on the origin and 

 development of the fibers in each particular case. This is very 

 clearly shown l)y the recent investigations of Esau (1938b, pp. 

 367-369) on the origin and development of the fibers in the stem 

 of tobacco. In this plant, Esau interprets the fibers morpho- 

 logically as part of the primary phloem rather than as "peri- 

 cyclic fibers," as has been done by certain workers. It is evident 

 from Esau's discussion of the literature that there is a great need 

 for a complete re-examination of the concept of "pericycle" from 

 an histogenetic point of view. Under such circumstances, the 

 classifications of fibers into "bast fibers" and "wood fibers" will 

 be followed in this book largely for the sake of simplicity and 

 convenience. 



2. Form and length of fihcrs. Fibers are classical examples 

 of typical prosenchymatous cells. Tlie ends are either acute or 



