284 Field, Forest, and Wayside Flowers 
tapering to a point at either end (Fig. 79). Most 
of these run lengthwise of trunk or boughs, and in 
Fic. 79.—Tracheids of the 
fir-tree. (Magnified.) 
their walls there are circles or 
ovals at regular distances 
apart. Each of these is a 
little plate of very thin tissue, 
set into the partition between 
two tracheids, and framed on 
both sides by a ring-shaped 
bulge in the tracheid-wall. 
The whole affair looks like 
a tiny circle surrounded by a 
halo. When the _ tracheids 
were young and full of pro- 
toplasm, plant-fluids were 
drawn through the thin spots, 
and thus a vital communica- 
tion was kept up through all 
the maturing tissue. But by 
the time the tracheid is fully developed the proto- 
plasm which has filled 
it disappears, and the mature 
wood of a cone bearer contains little else but a 
film of water on the tracheid-walls. So most of 
the ‘‘ bordered pits’’ 
vegetable economy. 
are no longer useful in the 
The Conifere combine the utmost grandure of 
