Ecological trends and relations to life forms

The phloem of all species consists mainly of parenchyma in which small groups of sieve-tubes are embedded (Figs. 13 and 14).

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Ecological trends in relation to vegetation zones are not recognizable. The shrubby species display some distinct characteristics: Polygala chamaebuxus reaches a relatively old age (>30 rings) and vessels have helical thickenings. Rings are indistinct and vessel density is low in the Australian shrub Polygala myrti-folia (cultivated in Europe).

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Left Fig. 13. Phloem with small groups of small sieve-tubes surrounded by larger parenchyma cells. Root collar of a 10 cm-high hemicryptophyte, dry meadow, mountain zone, Grisons, Switzerland. Polygala pede-montana, transverse section.

si Right Fig. 14. Phloem with small sieve tubes surrounded by larger parenchyma cells and ray dilatations. Stem of a 1 m-pa high shrub, cultivated, hill zone, Botanical Garden, Ticino, Switzerland. Polygala myr-tifolia, transverse section.

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