MICROSCOPY OF PAPER. 103 



less numerous and show larger pores more closely packed. 

 At the ends of the cells is often a long, tail-like point, and 

 the grating seen in the case of birch is absent. 



8. The Fibres of Straw and Esparto. — Paper made 

 from the stems of the grasses and grains is largely made 

 up of long slender bast-fibres knotted or thickened at 

 regular intervals (Fig. 41, a). The central canal is con- 

 stricted at these points and fine pores are present, passing 

 through the wall. The characteristic structures of such 

 tissues are, however, the cells from the epidermis, flat 

 and of somewhat variable length, with thick walls and 

 serrated edges (Fig. 41, c). 



In straw pulp a third type of cell is present, derived 

 from the internal pith layer. These are large, oval, 

 thin- walled cells with rounded ends (Fig. 41, J). Esparto 

 or alfalfa grass (Stipa tenacissima) may be distinguished 

 from straw by the absence of these pith cells, and by the 

 smaller size of the bast and epidermal elements. 



REFERENCES. 



Cross, C. F., and Bevan, E. J. A Text-book of Paper-making. 

 London, 1900. 



Herzberg, W. Papierpriifung. Berlin, 1902. 



Whitney, W. R., and Woodman, A. G. The Microscopic Exam- 

 ination of Paper Fibres, Technology Quarterly, XV, 1902, 272. 



