CELL-CONTENTS AND FORMS OF CELLS. 269 



circular, ellipsoidal or polygonal, depending upon the pressure 

 upon the walls and whether they are isolated or in groups. They 

 vary in diameter and length, and also in the thickness of the walls ; 

 while most bast fibers are between I and 2 mm. in length, they 

 may be more than 200 mm. in length, as in Boehmeria nivea. 

 The ends may be more or less obtuse or drawn out to a fine point ; 



FIG. 139. Transverse (t) and longitudinal (1) sections of commercial fibers: A, long 

 staple cotton from the seeds of Gossypium; B, Kentucky hemp, the bast of Cannabis 

 sativa; C, jute, the bast of Corchorus; D, sisal, the fibers from the leaves of the Century 

 plant (Agave rigida Sisalana) ; E, raphia, the outer layers of leaflets of Raphia. pedunculata; 

 F, ramie, the fibers from a Formosa nettle; G, Merino wool; H, silk; I, artificial silk, the 

 figure on the left showing a false lumen due to the infolding of the edges, f, fungal hyphae; 

 c, rosette aggregates of calcium oxalate; p, parenchyma cells. 



occasionally they are somewhat branched (Fig. 140). The pores 

 in surface view are narrow elliptical and arranged according to a 

 left-handed spiral. The spiral arrangement of the component 

 elements of the wall is supposed to give strength to the fibers, 

 and, according to Schwendener, they will sustain a weight nearly 

 equivalent to that of wrought-iron and steel. 



