80 
HISTOLOGY OF VEGETABLES. 
large pores. In all the examples above-mentioned, the 
cell wall is invariably present, but there are instances 
when the cells have become old, of the cell-wall dis- 
appearing, and true pores being formed. 
Woody Tissue. — This tissue, which makes up almost 
the entire bulk of certain plants, is by far the most use- 
ful and important to man of ail those occurring in the 
vegetable kingdom, since it supplies material to every 
branch of art, and to it we are indebted for our linen, 
ropes, cordage, &c., to say nothing of paper. 
It consists of elongated transparent tubes of great 
strength, but varying much in size in different plants ; 
each tube is more or less pointed at both extremities, 
and in some cases the tubular part has become almost 
solid by the internal deposition of new matter, so that 
the trace of the central cavity is only indicated by a line. 
Such tubes are remarkable for their toughness, and 
have received the name of fibres. The outer membrane 
of the fibre is generally structureless ; but in the Flax 
and other plants, in which the fibres are of great length, 
there are here and there traces of transverse markings. 
The fibres of Flax are aggregated together in bundles, 
and are separated from the plant for use by a process 
termed hackling, which may be described as an alterna- 
tion of beating and combing. In the rough condition, 
in which it is imported from Russia, the fibres have 
been, to a certain extent, separated by hackling. On its 
arrival here, it is again subjected to maceration, to a 
repetition of the hackling, and to the bleaching process 
in order to reduce it to the white silky condition 
