60 THE OAK 
various groups of smaller vessels—the groups being 
rounded, or in radial rows, or curved or oblique rows. 
Successive sections prove that the vessels in the 
bundle change in number—z.e. there are fewer when 
passing from stem to leaf. A vessel may end in an 
interpectinating, pointed, terminal cell; or it may 
branch, as it were, dichotomously, owing to fusions with 
other similar elements; or such a fusion may occur 
lower down, the original vessel ending blindly. 
In the vicinity of the reticulated and first pitted 
vessels, following on the spiral vessels, we find libriform 
fibres, tracheids, wood parenchyma, and_ secondary 
rays of parenchyma; the tracheids are especially in 
the neighbourhood of the vessels (see fig. 14). 
The tracheids are long cells with gradually taper 
ends, and the walls rather thick but by no means ob- 
securing the lumen; on the walls are numerous, usually 
elongated, oblique or horizontai bordered pits. ‘These 
pits occur whether the next element is a tracheid, a 
vessel, or fibres or cells of any kind (fig. 16, #r). 
The length of the tracheids varies, and the diameter 
is also variable. 
The libriform fibres are also long cells, but often 
more pointed at the ends, and their very thick walls 
almost obliterate the lumen (fig. 16, f); their length is 
about that of the tracheids, but slit-like, small, simple 
pits are rare on their walls. Inthe wood of later years, 
however, the lengths may be different. 
There are also elements which stand midway between 
