398 



THE STRUCTURE OF ECONOMIC PLANTS 



(Chapter I), but it is clear that the first phase of growth involves a 

 rapid elongation and enlargement of the fiber cell and a slight 

 increase in the thickness of the cell wall resulting from additions of 

 cellulose to the middle lamella. Adjacent to the middle lamella 



D 



\ 



1 2 3 



p w 

 s w 



Fig. 2.03. Structure of fiber: A, transection of group of fibers showing middle lamellae 

 and concentric layers of secondary wall with delicate reticulated structure; B, transection 

 of single fiber showing primary wall and two layers of secondary wall, innermost of which is 

 divided into seven lamellae; C, diagram of fiber in transection showing lumen, lu, middle 

 lamella, m Im, primary wall, p w, and secondary wall, s w; D, longitudinal views of ends 

 of fibers (fibers 1-4 illustrate abnormal forms from basal portion of stem, while those in 

 group 5 are normal types) ; E, F, and G, transections of progressive stages in development 

 of fiber ; E, transections of young fibers showing, a, fiber with infolded inner wall layer ; 

 b, point of fiber in transection, and c, fiber cells still unthickened ; F, transection of two 

 mature fibers from lower part of stem showing infolded inner wall layers ; G, transection of 

 group of fibers from uppermost part of mature stem showing thickened primary wall, very 

 thick secondary wall, and formation of some intercellular spaces, i sp. (/I, B, C, D, redrawn 

 from Herzog ; A after Reimers ; B after Krabbe ; Technologie des Textilfasern, Julius Springer ; 

 E, F, and G, after Tammes, Der Flacksstengel.^ 



there may be more or less pectic material which does not form a 

 definite layer but is intermixed with the cellulose. 



Cell wall formation is usually the result of an intussusception or 

 apposition of wall substances, and it is by means of such processes 

 that the primary and secondary walls of the fiber are probably laid 

 down. However, it has been suggested by Aldaba (i) and Ander- 

 son Ql) that these processes can hardly account for the formation of 

 the successive lamellae which constitute the thickenings of the 



