The Tracheid
It is a common belief that the wood of angiosperms
exclusively contains fibers and vessels and that the
wood of gymnosperms contains only tracheids, which
are cells that have the dual purpose of sap conduc-
tion and support. There are crossover plants that have
both fibers and tracheids in their wood, like some
species of Magnolia, showing that these contrasting
anatomies evolved in stages. Indeed, there is not one
ancestral plant that was the first to 'invent' wood;
rather, wood has arisen from various plant families inde-
pendently, which is rather amazing, given all the similar
building blocks used to grow the woods of the world.
This image shows tracheids in larch (Larix decidua). On
the left, see the uniformity of typical coniferous wood,
with a transition across an annual ring (from earlywood
to latewood). There is one easy-to-spot larger hole that is
a resin duct. On the right-hand side is a closer-up image
of the earlywood/latewood section, where you can see
the spiraling pattern inside each tracheid. Like the fibers
found in the wood of angiosperms, due to the need for
tracheids to supply structural strength, there is in this
conifer a spiraling matrix of cellulose strands, set within
lignin in these tracheids and glued together with pectin.
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