Characteristics of the phloem the cortex and the pith

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Following Metcalfe and Chalk (1957), the cortex is divided in three zones (Fig. 1): Under the epidermis are thin-walled parenchymatic cells (assimilating tissue). Below is a belt with central vascular bundles (phloem in the center), embedded in slightly sclerotized cells. An endodermis seperates the cortex from the cork zone consisting square, pitless prismatic cells (shoe box-like; Fig. 6). This zone arises from the pericycle zone, which consists mainly of spirally thickened, very long, unligni-fied cells. The phloem consists of radially grouped sieve tubes and parenchyma and spiral cells (Fig. 6).

Thin-walled parenchymatic cells with scattered "spiral cells" (Metcalfe and Chalk 1957) characterize the inner part of the pith (Figs. 7 and 8). Cell walls of some pith cells have thin spiral thickenings (Fig. 9). A belt of thick-walled cells is typical for the border zone towards the xylem. In both parts collateral vascular bundles occur (Figs. 1 and 10).

100 Mm spiral cell

100 Mm

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Fig. 9. Thin spirals on the walls of a parenchyma cells in the pith. 60 cm-high dwarf shrub, growing in the understory, tropical greenhouse, Botanical Garden Zürich, Switzerland. Nepenthes ampullaria, radial section.

Fig. 8. Spiral cell embedded in parenchyma cells of the pith. The spirals have been displaced by the mechanical force of the cutting knife. 60 cm-high dwarf shrub, understory, tropical greenhouse, Botanical Garden Zürich, Switzerland. Nepenthes am-pullaria, transverse section.

^spiral cells

Left Fig. 6. The bark is composed of a phloem with small sieve-tube groups, a pericycle zone with some "spiral cells", a phellogen, a phellem, an endodermis and a cortex. 60 cm-high dwarf shrub, under-story, tropical greenhouse climate, Botanical Garden Zürich, Switzerland. Nepenthes alata, transverse section.

Right Fig. 7. Spiral cell of the pericycle zone. The spirals of the extremely long cells are loosely connected with the primary walls. 60 cm-high dwarf shrub, understory, tropical greenhouse climate, Botanical Garden Zürich, Switzerland. Nepenthes alata, radial section.

Fig. 10. Collateral vascular bundle in the pith. The bundle is surrounded by thick-walled cells. 60 cm-high dwarf shrub, un-derstory, tropical greenhouse, Botanical Garden Zürich, Switzerland. Nepenthes ampullaria, transverse section.

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Fig. 9. Thin spirals on the walls of a parenchyma cells in the pith. 60 cm-high dwarf shrub, growing in the understory, tropical greenhouse, Botanical Garden Zürich, Switzerland. Nepenthes ampullaria, radial section.

Fig. 10. Collateral vascular bundle in the pith. The bundle is surrounded by thick-walled cells. 60 cm-high dwarf shrub, un-derstory, tropical greenhouse, Botanical Garden Zürich, Switzerland. Nepenthes ampullaria, transverse section.

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