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Sp. 
Fia. 28.—The various chief elements of the wood of the 
oak, isolated by maceration, and highly magnified. f, a 
fibre, distinguished by its thick walls, simple slit-like 
pits, and no contents; ~.p, part of a row of wood-paren- 
chyma cells, with simple pits, and containing starch in 
winter; tr, a tracheid, distinguished from the fibre 
especially by its bordered pits; p.v, part of a rather large 
pitted vessel, made up of communicating segments, each 
of which corresponds toa tracheid, and has bordered pits 
on its walls; sp, part of a spiral vessel. 
