Characteristics of the phloem and the cortex

The conifer-like, vesselless wood has distinct rings with distinct earlywood and latewood (Figs. 1 and 2). Tracheids are thin- to thick-walled and often contain gelatinous layers (tension wood; Fig. 3). Radial cell walls of tracheids have distinctly bordered, round pits in the latewood and scalariform pits in the earlywood (Fig. 4). Axial parenchyma is rare or absent. Rays occur in two forms: uniseriate rays with upright cells and larger, heterocel-lular rays (2-4 square or upright marginal cells) with 3-6 cells width (Figs. 5 and 6). Large, simple pits arranged in axial rows occur in cells of uniseriate rays (Fig. 7). Crystals are absent.

The phloem is simply structured. Parenchyma cells and sieve-tube element cells cannot be distinguished. Large rays are dilated. A belt of thick-walled sclereids is outside the phloem (Fig. 8). The cortex and the pith contain isolated, irregularly formed sclereids (Fig. 9). Prismatic crystals mainly occur in the belt of sclereids.

Fig. 3. Tension wood. Tracheids with gelatinous layers (blue). For origin see Fig. 1. Transverse section.

tr Left Fig. 1. Conifer-like xylem, consisting of tracheids, with distinct annual rings. Branch with a diameter of 3 cm of a 4 m-high tree, hill zone, cultivated, Botanical Garden Zürich, Switzerland. Trochodendron aralioides, transverse section.

Right Fig. 2. Vesselless xylem. Rings with distinct earlywood and latewood. For origin see Fig. 1. Transverse section.

Fig. 3. Tension wood. Tracheids with gelatinous layers (blue). For origin see Fig. 1. Transverse section.

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Fig. 4. Tracheids with scalariform bordered Fig. 5. Rays of two types: Uniseriate and pits in the earlywood and round pits in the multiseriate rays with 3-5 cells in width latewood. For origin see Fig. 1. Radial sec- and partially with sheet cells. For origin see tion. Fig. 1. Tangential section.

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