Characteristics of the xylem

Annual rings are present in most species (Figs. 1 and 2) but are indistinct in Polygala myrtifolia (Fig. 3). Rings are very small in Polygala chamaebuxus (Fig. 2) at natural sites. Ring boundaries are marked by semi-ring-porosity; vessels are arranged mostly solitary (Figs. 1-3, 6 and 7). The earlywood vessel diameter of the majority of species varies from 30-40 pm. Vessel density varies mostly from 200-300/mm2, but it is below 100/mm2 in Polygala myrtifolia (Fig. 3). Vessels contain exclusively simple perforations (Fig. 4). Inter-vessel pits are mostly round and large (3 pm) in alternating position (Fig. 5). They are vestured in Polygala chamae-buxus. Distinct helical thickenings occur in Polygala chamaebuxus (Fig. 4). Vessels of a few species contain dark-staining substances, e.g. Polygala tenuifolia.

Fibers are mostly thin- to thick-walled (Figs. 6 and 7), but are thick-walled in Polygala myrtifolia (Fig. 3) and thin-walled in Polygala alpestris. Parenchyma is absent or apotracheal in aggregates (Figs. 6 and 7). Rays are absent or difficult to recognize in Polygala chamaebuxus, and are uni- to biseriate in all other species (Figs. 8-10). Rays are mostly homocellular with square and upright cells (Fig. 11) but are occasionally heterocellular with a few square or procumbent cells (Polygala myrtifolia; Fig. 12). Crystals are absent in all species.

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Polygala Myrtifolia Sur Tige

Fig. 3. Indistinct rings in a diffuse-porous wood. Stem of a 1 m-high shrub, cultivated, Botanical Garden, Ticino, Switzerland.

Polygala myrtifolia, transverse section.

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Fig. 4. Vessel with a simple perforation, large, round intervessel pits and thick helical thickenings. Root collar of an 8 cm-high chamaephyte, on rock, subalpine zone, Grisons, Switzerland. Polygala chamaebux-us, radial section.

Fig. 3. Indistinct rings in a diffuse-porous wood. Stem of a 1 m-high shrub, cultivated, Botanical Garden, Ticino, Switzerland.

Polygala myrtifolia, transverse section.

Left Fig. 1. Distinct rings of a semi-ring-porous xylem. Root collar of a 5 cm-high hemicryptophyte, meadow, alpine zone, Grisons, Switzerland. Polygala alpestris, transverse section.

Right Fig. 2. Distinct rings of a semi-ring-porous xylem containing more than 30 rings. Root collar of a 8 cm-high chamae-phyte, on rock, subalpine zone, Grisons, Switzerland. Polygala chamaebuxus, transverse section.

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Fig. 4. Vessel with a simple perforation, large, round intervessel pits and thick helical thickenings. Root collar of an 8 cm-high chamaephyte, on rock, subalpine zone, Grisons, Switzerland. Polygala chamaebux-us, radial section.

Fig. 5. Large, round pits on vessels and fibers. Root collar of a 10 cm-high hemicryp-tophyte, dry meadow, mountain zone, Grisons, Switzerland. Polygala pedemontana, radial section.

Left Fig. 6. Apotracheal parenchyma in aggregates in a semi-ring-porous xylem. Root collar of a 10 cm-high hemicryptophyte, dry meadow, mountain zone, Grisons, Switzerland. Polygala pedemontana, trans-

verse section.

Right Fig. 7. Apotracheal parenchyma in a semi-ring-porous xylem. Root collar of a 15 cm-high hemicryptophyte, dry meadow, mountain zone, Caucasus, Georgia. Polygala transcaucasica, transverse section.

Left Fig. 6. Apotracheal parenchyma in aggregates in a semi-ring-porous xylem. Root collar of a 10 cm-high hemicryptophyte, dry meadow, mountain zone, Grisons, Switzerland. Polygala pedemontana, trans-

verse section.

Right Fig. 7. Apotracheal parenchyma in a semi-ring-porous xylem. Root collar of a 15 cm-high hemicryptophyte, dry meadow, mountain zone, Caucasus, Georgia. Polygala transcaucasica, transverse section.

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