Characteristic of well-grown individuals are the tangentially arranged layers of parenchyma and sieve tubes (Fig. 8). Sieve tubes
phg duct sc are collapsed in the older phloem (Fig. 9). Sclerenchyma occurs in large bands (Fig. 9) and in large groups (Fig. 10). Large mucilage ducts are specific for Ulmus (Fig. 11). Large prismatic crystals occur in the axial parenchyma and the sclerenchyma (Fig. 10).
Left Fig. 8. Young phloem in the cambial zone. Groups of small sieve tubes and large parenchyma cells alternate tangentially. Sclerotization of parenchyma cells occurs after a few years (red). Stem of a 6 m-high tree, Quercus pubescens forest, hill zone, Val-tellina, Italy. Ulmus minor, transverse section.
Right Fig. 9. Large, tangential, dense bands of sclerotized cells are located outside of the unlignified phloem. Sieve tubes are collapsed. Stem of an 8 m-high tree, Quercus pubescens forest, hill zone, Trento, Trentino, Italy. Celtis australis, transverse section.
Left Fig. 10. Large, tangentially arranged groups of sclerenchyma cells with many prismatic crystals. Stem of a 6 m-high tree, dry hill zone, Botanical Garden Tbilisi, Georgia. Celtis caucasica, transverse section.
Right Fig. 11. Phloem with large mucilage ducts. Stem of a 6 m-high tree, Quercus pubescens forest, hill zone, Valtellina, Italy. Ulmus minor, transverse section.
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