The endodermis of the needle in pine consists of a continuous sheath of parenchymatous cells in which the water transport can occur only through the cytoplasma or across the radial walls. Topochemical results have shown that the radial cell walls, in contrast to the tangential ones, contain lignin as well as other aromatic substances and consequently permit only a very limited permeability. The water transport in needles of pine without an epidermis is accompanied by a high temperature coefficient and a sensitivity towards inhibitors. On the basis of these results as well as the behaviour of needles after an abrupt break in transpiration and the fact that the plasma in the endodermis has a high permeability, it can be concluded that in the endodermis of the needle the water transport occurs mainly in the cytoplasm.
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