Characteristics of the xylem and phloem

Various species of Acer

All species are diffuse-porous and have distinct annual rings (Fig. 1). Ring boundaries are indicated by tangentially flat fibers in the latewood. Earlywood vessel diameter varies from 4080 pm and vessel density from 50-80/mm2 (Fig. 1). Vessels have simple perforations, large intervessel pits and helical thickenings (Fig. 2). In specimens with large rings, patches of relatively thin-walled fibers alternate with patches of thicker walled fibers (Figs. 1 and 3). Parenchyma is rare, scanty paratracheal or apo-tracheal diffuse and often difficult to recognize (Fig. 3).

2-5-seriate homocellular rays with procumbent cells are characteristic of the family (Figs. 3, 4 and 5). Crystals are absent, rare or in axially chambered cells (Fig. 6). Phloem structures are relatively uniform. Sieve tubes and parenchyma cells and bands of sclerenchyma are arranged in tangential rows (Fig. 7). Prismatic crystals are frequent (Fig. 8) and occasionally located in axial chambers.

Fig. 3. Rare, scanty paratracheal parenchyma (blue cells). Stem of a 10 m-high tree, Carpinus forest, hill zone, Burgundy, France. Acer campestre, transverse section.

Fig. 4. Uni- and bi-seriate rays. Stem of a 6 m-high tree, garden, hill zone, Bern, Switzerland. Acer negundo, tangential section.

Left Fig. 1. Diffuse-porous xylem with distinct ring boundaries. Patches of relatively thin-walled fibers alternate with patches of thicker walled fibers. Low vessel density is characteristic. Stem of an 8 m-high tree, canyon, hill zone, Sofia, Bulgaria. Acer ta-taricum, transverse section.

Right Fig. 2. Vessel with helical thickenings and ray cells in the cross field with slightly enlarged pits. Homocellular ray with procumbent cells. Stem of a 6 m-high tree, canyon, Mediterranean zone, Treonik, Macedonia. Acer obtusatum, radial section. f

Fig. 5. 1-5-seriate rays. Stem of a 5 m-high tree, maccia, Mediterranean zone, Bitola, Macedonia. Acer heldreichii, tangential section.

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