sp. 



p.v. 



FIG. 28. The various chief elements of the wood of the 

 oak, isolated by maceration, and highly magnified. /, a 

 fibre, distinguished by its thick walls, simple slit-like 

 pits, and no contents ; n\j>, 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 to a tracheid, and has bordered pits 

 on its walls; sp, part of a spiral vessel. 



