Structure of coniferous wood

In coniferous wood – on the evolutionary scale, much older than deciduous wood – the structure is much simpler. The same cell type (tracheids) is responsible for both sap conductions and providing the wood’s strength.
The only differences are in the thickness of the cell walls. During the growth period in spring, large-pore, thin-walled cells are formed that conduct the water absorbed by the roots to the needles. In late summer, more thick-walled wood cells tend to be formed that are necessary for the tree’s stability and strength.
This is what creates the classical grain of the wood, as the summer wood, made up of thick-walled cells, appears darker than the thin-walled springwood. In fact, there is absolutely no difference in colour between the individual wood cells.

In evolutionary terms, the conifers are much older than deciduous trees and so have a much simpler anatomical cell structure, consisting of only two cell types.

Tracheids: long cells which taper to a point at the ends and are only filled with water or air. They combine water conducting and hardening functions and make up around 90–100 % of the wood’s substance. Fluid exchange from cell to cell occurs via openings working like non-return valves, the so-called pits. In the rays, they operate as transverse tracheids transporting water and mineral nutrients in a radial direction. They make up 4–12 % of the total wood substance.

Parenchyma cells: In longitudinal section, these are mostly rectangular cells that a responsible for conducting nutrients and storing starch and fats. In a radial direction, as ray parenchyma, they make up majority of the ray tissue. The parenchyma cells that surround the resin ducts work as an epithelium and produce the resin which they discharge into the resin duct.

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Corss-section of a spruce
Photo: Grosser, München