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, @). 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, ¢). 
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, 6). 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. 
HeErzpBerc, W. Papierpriifung. Berlin, 1g02. 
Watney, W. R., and Woopman, A. G. The Microscopic Exam- 
ination of Paper Fibres, Technology Quarterly, XV, 1902, 272. 
