Characteristics of the xylem

Ring boundaries are distinct in most species (Figs. 1-4 and 6) except in the Quercus species of the subgenera sclerophyllodris (Fig. 5). All Fagus species are semi-ring-porous (Fig. 6). Casta-nea (Fig. 1) and all Quercus species are ring-porous (Figs. 2-4) except those of the subgenera sclerophyllodris (Fig. 5), which are diffuse-porous. Latewood vessels are arranged solitary and in small groups in Fagus (Fig. 6), or are arranged in radial, diagonal or dendritic patterns as in Castanea and Quercus (Figs. 1-4). Earlywood-vessel diameter between 50-90 pm is characteristic for Fagus and 100-200 pm for Quercus. Vessels of Castanea and Quercus have exclusively simple perforations, while those of Fagus are a combination of simple and scalariform (Fig. 7). Vessel pits are arranged opposite in Fagus but alternate in Quercus and

Left Fig. 1. Ring-porous xylem with distinct annual ring boundaries. Latewood vessels are arranged in diagonal to radial strips. Vessel size continuously decreases from earlywood to latewood. Stem of a young 15 m-high tree, Chestnut forest, hill zone, Locarno, Ticino, Switzerland. Castanea sativa, transverse section.

Right Fig. 2. Ring-porous xylem with distinct annual ring boundaries. Latewood vessels are arranged in diagonal to radial strips. Vessel size continuously decreases from earlywood to latewood. Parenchyma cells form intra-annual tangential bands. Stem of a young 15 m-high tree, Quercus cerris forest, Mediterranean, Tuscany, Italy. Quercus cerris, transverse section.

Castanea. Ray-vessel pits are enlarged in all species analyzed. Their form varies between round, upright and prostrate oval (Figs. 8 and 9). Vessels of all species contain thin-walled tylosis

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