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102 ELEMENTS OF APPLIED MICROSCOPY. 
swellings at intervals along their course are also present 
in birchwood. 
The small, broad cells of the fibrovascular bundles 
are more characteristic. In birch they are very numer- 
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Fic. 41.—CELLS oF Straw. (After Herzberg.) 240 diameters. 
ous, and are dotted with minute pores arranged in rows 
at right angles to the long axis of the cell (Fig. 4o). The 
distribution of these pores is somewhat irregular. At 
‘the ends of the cell the cross-hatched transverse walls 
are sometimes seen. In poplar the cells of this type are 
