MICROSCOPY OF PAPER. ror 
. or oval scar-like pits arranged in regular rows over their 
surface. In the case of pine, lattice-like areas with ob- 
long openings appear at intervals; but the presence of 
long cells mainly of a single type and with discoid mark- 
ings is the characteristic of the Conifers in general. 
7. The Structure of the Angiosperms.—Pulp made 
from the commoner Angiospermous trees shows two 
distinct elements, long narrow fibres and short broad 
Fic, 40.—Tracuem oF Bircw. (After Herzberg.) 240 diameters. 
cells with ,characteristic markings. The two species 
most in use for cheap grades of paper are poplar 
and birch; the longer fibres are very similar in both, 
having a central canal of variable width and ends 
sometimes rounded and sometimes tapering to a point. 
The more thin-walled of these fibres often show rounded 
and oval pores penetrating the wall. Smaller fibres with 
