Ecological trends in the xylem and phloem
The phloem and the cortex are in the majority of analyzed species simply structured by the radial arrangement of parenchyma and sieve tubes. Groups of sclereids occur in all species and are small (Fig. 12) except in Reseda luteola where they occupy the major part of the bark (Fig. 13).
Ecological trends could not be recognized in the limited amount of sample material analyzed.
Left Fig. 12. Bark with radially oriented rows of parenchyma cells, groups of small sieve tubes and a few sclerenchyma cells (red), located in the outer part of the phloem. Rays are slightly dilated. 30 cm-high plant on a gravel place in the hill zone of the southern Alps. Reseda luteola, transverse section.
Right Fig. 13. Intensively sclerotized bark. Sclerenchyma cells have extremely thick cell walls. 70 cm-high, fast growing plant on a ruderal site in the submediterranean zone of the southwestern Alps. Reseda lutea, transverse section.
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