MICROSCOPY OF PAPER. 



lot 



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 



Fig. 40. — ^Tracheid of Birch. (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 



