Characteristics of the xylem

Annual rings occur in the present material in a few species of the arid, Mediterranean and subtropical climate (Figs. 1 and 2). Circle-like intra-annual bands with successive cambia should not be confused with annual rings (Fig. 3). Amaranthaceae do not get very old. The maximum age found was 21 years (Haloxy-lonpersicum, 3 m-high tree). Most species with countable rings do not exceed 6 years. Ring-boundaries are defined by semi-ring porosity (Fig. 2) or a zone of thick-walled fibers (Fig. 1). Rings are indistinct or absent in 60 of the 64 species analyzed.

Vessels of most species are solitary (Fig. 2) or are arranged in mostly short (2-4 vessels) radial multiples (Fig. 3). Only 5 species have vessels in long radial multiples (Fig. 4). The diameter of earlywood vessels varies from 15-150 pm. Earlywood vessels are smaller than 20 pm in small plants (Polycneum arvense, Che-neloides tomentosa and Kochia prostrata; Fig. 2) as well in the dwarf shrubs Arthrocneumum glaucum and Suadeapruniosa. The diameter of earlywood vessels of the majority of species varies between 25-70 pm. The diameter in the liana Bosea cypria exceeds 100 pm. Vessel density varies in the majority of analyzed species between 100-200/mm2. In 15 species it exceeds 200/ mm2. Vessels are thin- to thick-walled (Fig. 4) or thick-walled (39 species; Fig. 5). Vessels contain exclusively simple perforations mainly in a vertical position (Fig. 6). Inter-vessel pits are predominantly small and round (Fig. 6), locally slightly scalari-form e.g. in Patellifoliaprocumbens and almost scalariform along the whole radial vessel wall in Chenopodium bonus-henricus (Fig. 7). Vestured pits were not clearly visible with the light microscope even on material stained only with safranin.

Dark-stained substances in the center of the stem (heartwood) are quite frequent in dwarf shrubs and shrubs (Fig. 8), but never in herbs. Small, thin-walled, unlignified tylosis can be found in Amaranthus blithum, Amaranthus hybridus, A. retroflexus, Achy-ranthes aspera, A. sicula, Bosea cypria and B. yervamora (Fig. 9).

In all species the radial walls of fibers are perforated by very small slit-like or round pits (<2 pm; Fig. 24). Fibers are in the majority of analyzed species thin- to thick-walled (30 species; Figs. 4 and 29) or thick-walled (28 species; Fig. 10). Fibers are missing in Amaranthus blithum, A. standleyanus, Chenopodium bonus-henricus and C. glaucum. The distribution of axial parenchyma is paratracheal (Figs. 4, 10 and 29) or pervasive (Amaranthus blithum, A. standleyanus, Chenpodium bonus-henricus and C. glaucum; Fig. 11). Xylem components are rarely storied unlike the parenchyma cells of the stem-intern phloem, which are mostly storied (Fig. 12).

ds cry r ds cry r

Achyranthes Stem Anatomy

Fig. 1. Distinct rings in the rayless xylem of a species with diffuse (foraminate) dispersed vascular bundles. The ring boundary is characterized by thick-walled latewood and thin-walled earlywood fibres. Stem of a 50 cm-high dwarf shrub, seashore with brackish water, Mediterranean zone, Nar-bonne, France. Arthrocneumum fruticosum, transverse section.

Fig. 1. Distinct rings in the rayless xylem of a species with diffuse (foraminate) dispersed vascular bundles. The ring boundary is characterized by thick-walled latewood and thin-walled earlywood fibres. Stem of a 50 cm-high dwarf shrub, seashore with brackish water, Mediterranean zone, Nar-bonne, France. Arthrocneumum fruticosum, transverse section.

Fig. 2. Recognizable rings in the xylem. The ring boundary is characterized by an indistinct, semi-ring porosity. Between the thick-walled lignified vessels with a diameter < 20 pm occur thin-walled pervasive parenchyma cells. Root collar of a 10 cm-high dwarf shrub in the cold steppe, subalpine zone, Mongolia. Kochia prostrata, transverse

Fig. 3. Intra-annual growth zones produced by successive cambia. The radial dimension of the two outermost blue and green zones are complete, but unlignified. Two stem-internal cambia are active. The vessels stay solitary or in short radial multiples. 40 cm-high annual plant, ruderal site, hill zone, Jena, Germany. Chenopodium urbicum, transverse section.

Xylem Vessels

Fig. 4. Vessels of the xylem stay in long radial multiples which are accompanied by paratracheal parenchyma. Xylem fibres around the vessels are fairly small and intensively lignified, conjunctive parenchyma cells (at the periphery of the phloem) are larger and less lignified. 50 cm-high annual plant, ruderal site, hill zone, Birmensdorf, Switzerland. Atriplex patula, transverse section.

Fig. 4. Vessels of the xylem stay in long radial multiples which are accompanied by paratracheal parenchyma. Xylem fibres around the vessels are fairly small and intensively lignified, conjunctive parenchyma cells (at the periphery of the phloem) are larger and less lignified. 50 cm-high annual plant, ruderal site, hill zone, Birmensdorf, Switzerland. Atriplex patula, transverse section.

Fig. 5. Thick-walled vessels are surrounded by parenchyma cells. Fibres in the tangential band are fairly thick-walled. Conjunctive parenchyma cells are thin-walled and unlignified. 30 cm-high annual plant, seashore, subtropical climate, Gran Canaria, Canary Islands. Atriplex semibaccata, transverse section.

Fig. 6. Vessels with simple perforations and round inter-vessel pits in opposite position. 40 cm-high annual plant, Ruderal site, subtropical climate, Gomera, Canary Islands.

Achyranthes aspera, radial section.

Scalariform Pits
Fig. 7. Vessels with almost scalariform inter-vessel pits. 40 cm-high annual plant, ruderal site, subalpine zone, Davos, Switzerland. Chenopodium bonus-henricus, radial section.

Fig. 8. Dark-stained substances (phenols?) in thick-walled vessels. Some conjunctive tissue is partially very thick-walled (scleren-chyma) but it is mostly thin-walled. 30 cm-high dwarf shrub, cold steppe, subalpine zone, Mongolia. Chenopodium frutescens, transverse section.

Fig. 9. Thin-walled, unlignified tyloses in vessels. 40 cm-high annual plant, ruderal site, subtropical climate climate, Gomera, Canary Islands. Achyranthes aspera, radial section.

storied i pa

Ph storied i pa

Herbal Plant Achyranthes Aspera

Fig. 12. Transition zone between thin-walled parenchymatic tissue (blue) and thick-walled xylem fibres. Parenchyma cells are divided and storied. 40 cm-high annual plant, ruderal site, subtropical climate, Gomera, Canary Islands. Achyranthes aspera, tangential section.

Fig. 10. Thick-walled fibres of the xylem surround vessels with paratracheal parenchyma. There are groups of phloem in tangential bands of conjunctive parenchyma cells. 40 cm-high dwarf shrub, seashore, subtropical climate, Gomera, Canary Islands. Suaeda vermiculata, transverse sec-

Fig. 11. Thick-walled vessels are surrounded by thin-walled pervasive parenchyma. 30 cm-high perennial plant, ruderal site, Mediterranean zone, Provence, France. Amaranthus blithum, transverse section.

Fig. 12. Transition zone between thin-walled parenchymatic tissue (blue) and thick-walled xylem fibres. Parenchyma cells are divided and storied. 40 cm-high annual plant, ruderal site, subtropical climate, Gomera, Canary Islands. Achyranthes aspera, tangential section.

Ray diversity is high. It varies from 1-2 to >10 cells (Figs. 1315). Many species contain large rays between vascular bundles, with 4-8 square and upright cells (Fig. 16). Ray and axial parenchyma are often confluent (Fig. 14). 23 of the 64 analyzed species are rayless e.g. some Atriplex and Chenopodium species, as well as Krascheninnikovia, Salsola kali and others (Figs. 2023). Ray cells are often thin-walled and unlignified (Fig. 15). Successive cambia are a characteristic of the majority of the Amaranthaceae but they are missing in the annual Polycneum arvense (Fig. 17). Vascular bundles are concentric and separated from each other in 19 species (Figs. 18 and 19), or concentric r v f

Islilrii M/fW

will!)) yt IWijlBI

iillllHH 1

Fig. 13. 1-3-seriate rays embedded in a thick-walled fibre tissue. 40 cm-high dwarf shrub, windy coast, subtropical climate, Gran Canaria, Canary Islands. Atriplex glauca, tangential section.

continuous in 40 species (Figs. 20 and 21) and arranged diffuse (foraminate) in 13 species (Fig. 22). The distribution of xylem and phloem varies within plants (Fig. 23) and between species. 45 of the 64 species have unlignified conjunctive tissue (Figs. 20 and 21). The other species show lignified conjunctive tissue cells with slightly thickened walls (Fig. 23). Prismatic crystals occur in 16 species (Fig. 24), partially in chambered cells (6 species, Fig. 25). 12 show crystal druses. Crystals are deposited in the rays (Fig. 24) or the interxylary parenchyma and small crystals surround the inner walls of vessels (Fig. 26).

40cm High Plants
The Xylem Vessels Amaranthus Spinosus
Fig. 14. 1-5-seriate rays. Some are confluent to the conjunctive axial tissue. 40 cm-high annual plant, ruderal site, hill zone, Grisons, Switzerland. Amaranthus retroflex-us, tangential section.

Fig. 15. 1- and multi-seriate rays with unlignified cell walls (blue). 40 cm-high annual plant, ruderal site, hill zone, Bir-mensdorf, Switzerland. Amaranthus viridis, tangential section.

Transverse Section Amaranthus Spinosus

Fig. 18. Stem internal xylem/phloem bands consist of concentrically arranged vascular bundles, separated by unlignified rays. Raylike between the tangential rows of vascular bundles is a thin-walled, unlignified conjunctive parenchymatic tissue. Vessels contain tylosis. Liana, hedge, Mediterranean, Paphos, Cyprus. Bosea cypria, transverse section.

Fig. 16. Parenchymatic tissue between vascular bundles. The parenchymatic zones can be interpreted as large rays. 30 cm-high perennial herb, ruderal site, Mediterranean zone, Provence, France. Amaranthus blithum, tangential section.

Fig. 17. An Amaranthaceae without successive cambia. Characteristic are radial multiple vessels with paratracheal parenchyma and 1-3-seriate rays. 15 cm-high annual plant, ruderal, Mediterranean, Provence, France. Polycneum arvense, transverse section.

Fig. 18. Stem internal xylem/phloem bands consist of concentrically arranged vascular bundles, separated by unlignified rays. Raylike between the tangential rows of vascular bundles is a thin-walled, unlignified conjunctive parenchymatic tissue. Vessels contain tylosis. Liana, hedge, Mediterranean, Paphos, Cyprus. Bosea cypria, transverse section.

Achyranthes Stem Anatomy

Fig. 19. Stem internal xylem/phloem bands consist of concentrically arranged vascular bundles, separated from each other. The conjunctive tissue consists of large, thin-walled, unlignified parenchymatic cells. Rays in a strict sense are absent, see Fig.16. 50 cm-high annual plant, field, moist site, Mediterranean, Haute Provence, France. Amaranthus hybridus, transverse section.

Fig. 19. Stem internal xylem/phloem bands consist of concentrically arranged vascular bundles, separated from each other. The conjunctive tissue consists of large, thin-walled, unlignified parenchymatic cells. Rays in a strict sense are absent, see Fig.16. 50 cm-high annual plant, field, moist site, Mediterranean, Haute Provence, France. Amaranthus hybridus, transverse section.

Fig. 20. Stem internal xylem/phloem bands consist of regularly concentrically arranged vascular bundles which are laterally connected by a band of fibres = concentric continuous. Between the tangential rows of intensively lignified xylem is a thin-walled, unlignified conjunctive parenchymatic tissue. Vascular bundles are solitary near the pith. 60 cm-high perennial dwarf shrub, dry canyon, subtropical climate, Dhofar, Oman. Aerva javanica, transverse section.

Fig. 21. Included phloem consisting of more-or-less concentrically arranged vascular bundles laterally connected by a band of fibres = concentric continuous. Between the tangential rows of intensively lignified xylem is a thin-walled, unlignified conjunctive parenchymatic tissue. 50 cm-high annual plant, ruderal site, coast, subtropical climate, Gran Canaria, Canary Islands. At-riplex semibaccata, transverse section.

rismatic crystals rismatic crystals

Fig Botanical

pith

Fig. 24. Prismatic crystals of different sizes in upright ray cells. Root collar of an annual, prostrate plant, windy coast, subtropical climate, Gran Canaria, Canary Islands. Cheneloides tomentosa, radial section.

Fig. 22. Diffusely distributed stem internal xylem/phloem. The vascular bundles are embedded in a conjunctive tissue consisting of thick-walled fibres. Annual 1 m-high plant on sandy places in arid region, Sahara, oasis, Algeria. Atriplex dimorphostegia, transverse section.

pith

Fig. 23. Variable distribution of the vascular bundles. Vascular bundles surround the pith in a circle. Vessels in the xylem are always irregularly distributed. Sieve tube groups (blue) are irregularly distributed around the pith and tend to be arranged in tangential rows later on. 70 cm-high annual plant, ruderal site, hill zone, Ticino, Switzerland. Chenopodium strictum, transverse section.

Fig. 24. Prismatic crystals of different sizes in upright ray cells. Root collar of an annual, prostrate plant, windy coast, subtropical climate, Gran Canaria, Canary Islands. Cheneloides tomentosa, radial section.

Suaeda Fruticosa
Fig. 25. Prismatic crystals in axially chambered square cells. The radial walls of the adjacent fibres (red) have small slit-like simple pits. 60 cm-high dwarf shrub, coast, Mediterranean, Mallorca, Spain. Suaeda fruticosa, radial section.
Suaeda Fruticosa
Fig. 26. Small prismatic crystals at the inner surface of thick-walled vessels, 1.5 m-high shrub, coastal dune, subtropical climate, Gomera, Canary Islands. Traganum moquinii, transverse section.

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Responses

  • john
    What are the two charecteristics of xylem?
    2 years ago

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