Characteristics of the xylem

Rayless vascular bundles without annual rings form a siphono-stele without an interfascicular cambium in Menyanthes and the annual shoot of Nymphoides peltata. (Figs. 1 and 2). They are laterally isolated in Menyanthes (Fig. 3), but form a more-or-less compact circle in the rhizome of Nymphoides (Fig. 5). A one-cell thick endodermis surrounds the siphonostele (Fig. 5). The xylem contains vessels with diameters <50 pm, which stay solitary or form radial multiples (Fig. 4). Radial vessel walls with scalariform perforations are characteristic of Menyanthes (Fig. 6). Solitary vessels with simple perforations are typical for Nymphoides (Fig. 7). Both species have scalariform inter-vessel pits (Figs. 6 and 7). Vessels are surrounded by a pervasive parenchyma (Figs. 4 and 5). Small strands of fibers occur along the pit side of the vascular bundles of Menyanthes (Fig. 4).

central cylinde?

central cylinder central cylinder central cylinde?

Fig. 3. Central cylinder with isolated vascular bundles. Large inter-cellular spaces in the cortex. Annual shoot of plant in a pond, hill zone, Botanical Garden Zürich, Switzerland. Nymphoides peltata, transverse section.

Fig. 1. Central cylinder with isolated vascular bundles. Large cortex with vascular bundles. Inter-cellular spaces exist in the cortex and the pith. Rhizome of plant in a pond in the mountain zone of the Alps, Switzerland. Menyanthes trifoliata, transverse section.

Fig. 2. Central cylinder with vascular bundles inside a cortex with small vascular bundles and many large inter-cellular spaces. Rhizome of plant in a pond, hill zone, Botanical Garden Zürich, Switzerland. Nymphoides peltata, transverse section.

Fig. 3. Central cylinder with isolated vascular bundles. Large inter-cellular spaces in the cortex. Annual shoot of plant in a pond, hill zone, Botanical Garden Zürich, Switzerland. Nymphoides peltata, transverse section.

Fig. 1. Central cylinder with isolated vascular bundles. Large cortex with vascular bundles. Inter-cellular spaces exist in the cortex and the pith. Rhizome of plant in a pond in the mountain zone of the Alps, Switzerland. Menyanthes trifoliata, transverse section.

metaxylem xy pith metaxylem xy pith

Left Fig. 4. Single rayless vascular bundle with vessels in radial multiples. On the outside is a thin-walled endodermis and on the inside few thick-walled lignified cells (red). Rhizome of plant in a pond, mountain zone, Alps, Switzerland. Menyanthes trifo-liata, transverse section.

Right Fig. 5. Central cylinder with vascular bundles inside a cortex with large intercellular spaces. The pith has no intercellular cavities. The central cylinder is surrounded by a one cell-thick, thin-walled endoder-mis. Rhizome of plant in a pond, hill zone, Botanical Garden Zürich, Switzerland. Nymphoides peltata, transverse section.

ivp ivp

ivp ihe ivp ihe

Left Fig. 6. Scalariform inter-vessel pits, scalariform perforations and helical thickenings. Rhizome of plant in a pond, mountain zone, Alps, Switzerland. Menyanthes trifoliata, radial section.

Right Fig. 7. Scalariform inter-vessel pits and simple perforations. Rhizome of plant in a pond, hill zone, Botanical Garden Zürich, Switzerland. Nymphoides peltata, radial section.

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