Vascular transfer cells in Angiosperm leaves A taxonomic and morphological survey

Summary A study of the fine structure of minor veins of mature leaves of 975 species and 242 families of Angiosperms shows that transfer cells are widespread amongst herbaceous Dicotyledons, are much rarer in woody Dicotyledons, and are virtually absent from the Monocotyledons. The evolutionary significance of the distribution of the cells amongst and within orders, families and minor groupings is discussed.Four types of transfer cell are recognized in minor veins, all possessing irregular ingrowths of wall material protruding into their protoplasts, and all being regarded as modified parenchyma of the minor vein. Two types occur in phloem. One (the A-cell), with ingrowths distributed right round its periphery, is associated specifically with the sieve elements. The other (the B-cell) occurs more generally throughout the phloem and has zones of wall ingrowths oriented towards sieve elements and their associated companion cells or A-cells. Two other types (C- and D-cells) occur in xylem parenchyma and bundle sheath respectively, and have ingrowths only on walls in contact with or in close proximity to vessels or tracheids. Each species has a characteristic combination of types of transfer cell. The variations encountered in the survey are classified. Consistent differences in the frequency and form of ingrowths are to be found between the different types of transfer cell of a single species, and between different species in respect to a particular type of transfer cell.The functional significance of transfer cells in minor veins is discussed in relation to the loading and unloading of the conducting elements and to the retrieval of extra-cytoplasmic solutes from the mesophyll and the transpiration stream.     

Zostera capensis setchell: III. Some aspects of wall ingrowth development in leaf blade epidermal cells

Summary The development of wall ingrowths in leaf blade epidermal cells of the marine angiospermZostera capensis was studied by electron microscopy. Prior to the appearance of ingrowths long profiles of endoplasmic reticulum cisternae become arranged peripherally closely following the contours of the walls. The plasmalemma assumes a wavy appearance and in regions where wall ingrowths first start forming (i.e., along the radial, inner tangential and transverse walls) the plasmalemma becomes separated from the walls by an undulating extracytoplasmic space. Small, irregular projections of secondary wall material make their appearance here. Paramural bodies, dictyosomes, endoplasmic reticulum (ER) and possibly also microtubules seem to be closely associated with the initiation and subsequent development of wall projections. As the cells mature, new ingrowths arise in a centrifugal direction along the radial and transverse walls. When wall ingrowths reach a certain stage of their development, mitochondria become strongly polarized towards them and become closely associated with the plasmalemma which ensheaths the ingrowths. There is often also a close association between ER cisternae and the involuted plasmalemma of the wall projections. Initially ingrowths are slender, curved structures, but become more complex as the cells mature. Ingrowths are most extensively developed along the inner tangential and transverse walls. As epidermal cells age there is a loss of wall material from the ingrowths. The probable significance of the formation of wall ingrowths in the epidermal cells is also discussed.     

Anatomy of Gymnosperms Endemic to China,II. Taiwania flousiana Gaussen (Taxodiaceae)

Taiwania Hayata contains two species: T.flousiana Gaussen and T. cryptomerioides Hayata, both endemic to China. T. flousiana was investigated with both light and scanning electron microscopes in respect to shoot apex, external and internal surfaces of leaf cuticle, primary leaf, juvenal and mature leaves, young stem, secondary phloem and wood of stem, etc, It is shown that the shoot apex consists of the following five regions: (1) the apical initials; (2) the protoderm, (3) the subapical moher cells;. (4) the peripheral meristem, and (5) the pith mother cells. The periclinal and anticlinal division of the apical initials takes place with approximately equal frequency. The juvenal leaf is nearly triangular or crescent-shaped in cross section and belongs to the leaf type II. The mature leaf is quadrangular in cross section (the leaf type I). There are a progressive series of changes in size and shape of the leaf cross section. The stoma of the mature leaf is amphicyclic and occasionally tricyclic. The crystals in the juvenal leaf cuticle are more abundant than those in the mature leaf cuticle. The transfusion tissue conforms to the Cupressus type. The structure of juvenal leaf is the nearest to that in Cunninghamia unicanaliculata D. Y. Wang et H. L. Liu, while the mature leaf is similar to that of the Cryptomeria. Sclerenchymatous cells of the hypodermis in the young stem comprise simple layers and are arranged discontinuously. No primary fibers are found in the primary phloem. Medullary sheath is present between the primary xylem and the pith. There are some sclereids in the pith. The secondary phloem of the stem consists of regularly alternate tangential layers of cells in such a sequence: sieve cells, phloem parenchyma cells, sieve cells, phloem fibers, sieve cells. The phloem fiber may be divided into thick-walled and thin-walled phloem fiber. The crystals of calcium oxalate in the radial walls of sieve cells are abundant. Homogeneous phloem rays are uniseriate or partly biseriate, 1-48 (2-13) cells high, and of 26-31 strips per square mm. Growth rings of the wood in Taiwania are distinct. The bordered pits on the radial walls of early wood tracheids are usually uniseriate, occasionally paired and opposite pitting. Wood parenchyma is present, and its cells contain brown resin substances. Their end walls are smooth, lacking nodular thickenings. Wood rays are homogeneous. Cross-field pits are cupressoid. Resin canals are absent. Based on the anatomy of Taiwania and comparison with the other genera of Taxodiaceae, the authors consider the establishment of Taiwaniaceae not reasonable, but rather support the view that the genus is better placed between Cuninghamia and Arthrotaxis in Taxodiaceae.     

Gibberellin signaling

A study of stem anatomy and the sclerenchyma fibre cells associated with the phloem tissues of hemp (Cannabis sativa L.) plants is of interest for both understanding the formation of secondary cell walls and for the enhancement of fibre utility as industrial fibres and textiles. Using a range of molecular probes for cell wall polysaccharides we have surveyed the presence of cell wall components in stems of hemp in conjunction with an anatomical survey of stem and phloem fibre development. The only polysaccharide detected to occur abundantly throughout the secondary cell walls of phloem fibres was cellulose. Pectic homogalacturonan epitopes were detected in the primary cell walls/intercellular matrices between the phloem fibres although these epitopes were present at a lower level than in the surrounding parenchyma cell walls. Arabinogalactan-protein glycan epitopes displayed a diversity of occurrence in relation to fibre development and the JIM14 epitope was specific to fibre cells, binding to the inner surface of secondary cell walls, throughout development. Xylan epitopes were found to be present in the fibre cells (and xylem secondary cell walls) and absent from adjacent parenchyma cell walls. Analysis of xylan occurrence in the phloem fibre cells of hemp and flax indicated that xylan epitopes were restricted to the primary cell walls of fibre cells and were not present in the secondary cell walls of these cells.     

Ultrastructure of transfer cells in spontaneous nodules of alfalfa (Medicago sativa)

Summary Spontaneous nodules were formed on the primary roots of alfalfa plants in the absence ofRhizobium. Histologically, these white single-to-multilobed structures showed nodule meristems, cortex, endodermis, central zone, and vascular strands. Nodules were devoid of bacteria and infection threads. Instead, the larger cells were completely filled with many starch grains while smaller cells had very few or none. Xylem parenchyma and phloem companion cells exhibited long, filiform and branched wall ingrowths. The characteristic features of both types of transfer cells were polarity of wall ingrowths, high cytoplasmic density, numerous mitochondria, abundant ribosomes, well-developed nucleus and nucleolus, and vesicles originated from rough endoplasmic reticulum. These results were compared with normal nodules induced byRhizobium. Our results suggest that xylem parenchyma and phloem companion transfer cells are active and probably involved in the short distance transport of solutes in and out of spontaneous nodules. Since younger nodules showed short, papillate, and unbranched wall ingrowths, and older tissue showed elongated, filiform and branched wall ingrowths, the development of wall ingrowths seemed to be gradual rather then abrupt. The occurrence of both type-A and -B wall ingrowths suggests that phloem companion transfer cells may be active in loading and unloading of sieve elements. Since there were no symbiotic bacteria and thus no fixed nitrogen, it is tempting to speculate that xylem parenchyma transfer cells may be re-transporting accumulated carbon from starch grains to the rest of the plant body by loading xylem vessels. Fusion of ER-originated vesicles with wall ingrowth membrane indicated the involvement of ER in the membrane formation for elongating wall ingrowths. Since transfer cells were a characteristic feature of both spontaneous andRhizobium-induced nodules, their occurrence and development is controlled by the genetic make-up of alfalfa plant and not by a physiological source or sink emanating from symbiotic bacteria.Abbreviations ATP adenosine triphosphate - ATPase adenosine triphosphatase - EH emergent root hair - EM electron microscope - Nar nodulation in the absence of Rhizobium - RT root tip - RER rough endoplasmic reticulum - YEMG yeast extract mannitol-gluconate     

A Preliminary Study on the Structure and Function of the Vascular Transfer Cells in Garlic Scape

The vascular transfer cells in garlic scape havebeen examined with electron microscope. Their structure, distributive feature and adenosine triphosphatase (ATPase) activity are studied. The mature vascular transfer cells exhibit the characteristic cell wall ingrowths. The cell contents include a large nucleus, dense cytoplasm and various normal organelles. It is notable that there are numerous mitochondria with well developed, cristae. Plasmodesmata are extensively present in the wall, and transfer cells are connected to adjacent cells by them. The senescing transfer cells become more vacuolated and have a large central vacuole and dense parietal cytoplasm. Their wall ingrowths seem to degenerate and finally disappear. The transfer cells show a particular pattern of distribution in the vascular bundle of the garlic scape. Some of them are present between the vessels of xylem and the sieve tubes of phloem. However, more abundant cell wall ingrowths occur on those walls which abut on, or are close to the vessel of xylem. The other transfer cells are located between the sieve tubes and parenehyma cells. The phloem transfer cell which is adjacent to sieve tube has developed from companion cell. All the transfer cells are mainly concerned with the loading and unloading of sieve tubes. And they may play an important role in facilitating intensive material transfer between two independent systems (i.e. the vessels and sieve tubes, the symplast and apoplast). The results of the cytochemical localization of ATPase using a lead precipitation technique exhibit strong enzyme activity on the plasmalemma of the transfer cells. It is suggested that the transfer cells are especially active in solute movement through them to which cellular energy metabolism coupled.     

绞股蓝营养器官中皂苷积累组织的超微结构观察

应用超薄切片和电镜技术观察了绞股蓝营养器官中积累皂苷的叶肉细胞、茎表皮细胞、茎皮层细胞和茎韧皮部细胞的超微结构.结果表明,幼叶叶肉细胞的液泡中具有蛋白体性质的电子致密物;随着叶的发育,叶绿体结构逐渐完善并积累淀粉粒;地上茎表皮细胞的外侧壁增厚,皮层细胞含叶绿体,液泡内有团块状结构;根状茎中的筛管细胞具有囊泡结构,其内的颗粒状内含物可释放至液泡和跨壁运输;韧皮薄壁细胞近细胞壁处具有丰富的细胞质和细胞器.但上述细胞中均未发现与皂苷积累相关的特殊电子致密物.     

PHLOEM OF SPHENOPHYLLUM

The phloem of most fossil plants, including that of Sphenophyllum, is very poorly known. Sphenophyllum was a relatively small type of fossil arthrophyte with jointed stems bearing whorls of leaves ranging in form from wedge or fan-shaped to bifid, to linear. The aerial stem systems of the plant exhibited determinate growth involving progressive reduction in the dimensions of the stem primary bodies, fewer leaves per whorl, and smaller and simpler leaves distally. The primary phloem occurs in three areas alternating in position with the arms of the triarch centrally placed primary xylem. Cells of the primary phloem, presumably sieve elements, are axially elongate with horizontal to slightly tapered end walls. In larger stems with abundant secondary xylem and secondary cortex or periderm, a zone of secondary phloem occurs whose structure varies in the three areas opposite the arms of the primary xylem, as opposed to the three areas lying opposite the concave sides of the primary xylem. The axial system of the secondary phloem consists of vertical series of sieve elements with horizontal end walls. In the areas opposite the protoxylem the parenchyma is present as a prominent ray system showing dilation peripherally. Sieve elements in the areas opposite the protoxylem arms have relatively small diameters. In the areas between the protoxylem poles the secondary phloem sieve elements have large diameters and are less obviously in radial files, while the parenchyma resembles that of the secondary xylem in these areas in that it consists of strands of cells extending both radially and tangentially. An actively meristematic vascular cambium has not been found, indicating that this layer changed histologically after the cessation of growth in the determinate aerial stem systems and was replaced by a post-meristematic parenchyma sheath made up of axially elongate parenchyma lacking cells indicative of being either fusiform or ray initials. A phellogen arose early in development in a tissue believed to represent pericycle and produced tissue comparable to phellem externally. Normally, derivatives of the phellogen underwent one division prior to the maturation of the cells. Concentric bands of cells with dark contents apparently represent secretory tissue in the periderm and cell arrangements indicate that a single persistent phellogen was present. Sphenophyllum is compared with other arthrophytes as to phloem structure and is at present the best documented example of a plant with a functionally bifacial vascular cambium in any exclusively non-seed group of vascular plants.     

白鲜营养器官解剖结构及其与白鲜碱的积累关系

应用植物解剖学、组织化学及植物化学方法对白鲜营养器官根、茎、叶的结构及其生物碱的积累进行了研究。结果显示:(1)白鲜根的次生结构以及茎和叶的结构类似一般双子叶植物;白鲜多年生根主要由周皮、次生韧皮部、维管形成层以及次生木质部组成,根次生韧皮部中可见大量的淀粉、草酸钙簇晶、韧皮纤维以及油细胞;茎由表皮、皮层、维管组织和髓组成;叶由表皮、栅栏组织、海绵组织和叶脉组成;在茎和叶初生韧皮部的位置均分布有韧皮纤维,在叶表皮上分布有头状腺毛和非腺毛;在茎和叶紧贴表皮处分布有分泌囊。(2)组织化学分析结果显示:在白鲜多年生根中,生物碱类物质主要分布在周皮、次生韧皮部、维管形成层和木薄壁细胞中;在茎中,生物碱主要分布在表皮、皮层、韧皮部、木薄壁细胞及髓周围薄壁细胞中;在叶中,生物碱主要分布在表皮细胞、叶肉组织和维管组织的薄壁细胞;此外在分泌囊和头状腺毛中亦含有生物碱类物质。(3)植物化学结果显示,秦岭产白鲜根皮/白鲜皮、根木质部、茎和叶中白鲜碱含量分别为0.041%、0.012%、0.004%和0.002%,其中木质部中白鲜碱含量和其他部分地区白鲜皮中白鲜碱含量类似。研究表明,在秦岭产白鲜营养器官中,除根皮/白鲜皮外,在根木质部亦含有大量的白鲜碱,且在茎和叶中亦含有一定的白鲜碱,具有潜在的开发利用价值。     

Transfer cells and nematode induced giant cells inHelianthemum

Summary The morphology of wall ingrowths in xylem and phloem transfer cells inHelianthemum is different. It is possible to use nematode infection to induce the formation of giant cells which abut both xylem and phloem elements to test whether ingrowth morphology is controlled by the solutes presumed to be transported across the plasmalemma of the cells. This experiment has been done and it is found that although wall ingrowths develop against both xylem and phloem, the giant cells exhibit only the ingrowth structure characteristic of xylem transfer cells.     

Ultrastructure of the haustorial interface and apoplastic continuum between host and the root hemiparasiteOlax phyllanthi (Labill.) R. Br. (Olacaceae)

Summary Structural features of haustorial interface parenchyma of the root hemiparasiteOlax phyllanthi are described. Walls contacting host xylem are thickened non-uniformly with polysaccharides, not lignin, and show only a thin protective wall layer when abutting pits in walls of host xylem vessels or tracheids. Lateral walls of interface parenchyma exhibit an expanded middle layer of open fibrillar appearance, sometimes with, but mostly lacking adjoining layers of dense wall material. Free ribosomes and rough endoplasmic reticulum are prominent and occasional wall ingrowths present. Experiments involving transpirational feeding of the apoplast tracers lanthanum nitrate or uranyl acetate to host roots cut below haustorial connections, indicate effective apoplastic transfer from host to parasite root via the haustorium. Deposits of the tracers suggest a major pathway for water flow through host xylem pits, across the thin protective wall layer, and thence into the haustorium via the electronopaque regions of the terminal and lateral walls of the contact parenchyma. Graniferous tracheary elements and walls of parenchyma cells of the body of the haustorium appear to participate in tracer flow as do walls of cortical cells, stele parenchyma and xylem conducting elements of the parasite root, suggesting that both vascular and non-vascular routes are involved in extracytoplasmic transfer of xylem sap from host to parasite. The Casparian strip of the endodermis and the suberin lamella of the exodermis of theOlax root act as barriers to flow within the system.     

Minor vein structure and sugar transport in Arabidopsis thaliana

Leaf and minor vein structure were studied in Arabidopsis thaliana (L.) Heynh. to gain insight into the mechanism(s) of phloem loading. Vein density (length of veins per unit leaf area) is extremely low. Almost all veins are intimately associated with the mesophyll and are probably involved in loading. In transverse sections of veins there are, on average, two companion cells for each sieve element. Phloem parenchyma cells appear to be specialized for delivery of photoassimilate from the bundle sheath to sieve element-companion cell complexes: they make numerous contacts with the bundle sheath and with companion cells and they have transfer cell wall ingrowths where they are in contact with sieve elements. Plasmodesmatal frequencies are high at interfaces involving phloem parenchyma cells. The plasmodesmata between phloem parenchyma cells and companion cells are structurally distinct in that there are several branches on the phloem parenchyma cell side of the wall and only one branch on the companion cell side. Most of the translocated sugar in A. thaliana is sucrose, but raffinose is also transported. Based on structural evidence, the most likely route of sucrose transport is from bundle sheath to phloem parenchyma cells through plasmodesmata, followed by efflux into the apoplasm across wall ingrowths and carrier-mediated uptake into the sieve element-companion cell complex. Received: 5 October 1999 / Accepted: 20 November 1999     

Comparative Microscopical Studies on the Patterns of Calcium Oxalate Distribution in the Needles of Various Conifer Species

The distribution of calcium oxalate crystals in various conifer needles is visualized by light and electron microscopy. Such crystals occur (1) in the vascular bundle, either intracellularly in the xylem or phloem parenchyma, or extracellularly within the radial phloem walls; (2) extracellularly on the outside of the walls of mesophyll cells which face the intercellular spaces; (3) and finally as numerous small crystals within the cell walls of the epidermal cells, especially in the cuticular layer. The development and distribution of these apoplastic crystals is described in detail. Some hypotheses are finally presented for interpretations of these unusual patterns of the crystallization of Ca-oxalate outside the vacuole. Possible evolutionary aspects of this feature among the different conifer families are also discussed.     

A xylem sap retrieval pathway in rice leaf blades: evidence of a role for endocytosis?

The structure and transport properties of pit membranes at the interface between the metaxylem and xylem parenchyma cells and the possible role of these pit membranes in solute transfer to the phloem were investigated. Electron microscopy revealed a fibrillar, almost tubular matrix within the pit membrane structure between the xylem vessels and xylem parenchyma of leaf blade bundles in rice (Oryza sativa). These pits are involved primarily with regulating water flux to the surrounding xylem parenchyma cells. Vascular parenchyma cells contain large mitochondrial populations, numerous dictyosomes, endomembrane complexes, and vesicles in close proximity to the pit membrane. Taken collectively, this suggests that endocytosis may occur at this interface. A weak solution of 5,6-carboxyfluorescein diacetate (5,6-CFDA) was applied to cut ends of leaves and, after a minimum of 30 min, the distribution of the fluorescent cleavage product, 5,6-carboxyfluorescein (5,6-CF), was observed using confocal microscopy. Cleavage of 5,6-CFDA occurred within the xylem parenchyma cells, and the non-polar 5,6-CF was then symplasmically transported to other parenchyma elements and ultimately, via numerous pore plasmodesmata, to adjacent thick-walled sieve tubes. Application of Lucifer Yellow, and, separately, Texas Red-labelled dextran (10 kDa) to the transpiration stream, confirmed that these membrane-impermeant probes could only have been offloaded from the xylem via the xylem vessel-xylem parenchyma pit membranes, suggesting endocytotic transmembrane transfer of these membrane-impermeant fluorophores. Accumulation within the thick-walled sieve tubes, but not in thin-walled sieve tubes, confirms the presence of a symplasmic phloem loading pathway, via pore plasmodesmata between xylem parenchyma and thick-walled sieve tubes, but not thin-walled sieve tubes.     

HYPERPLASTIC PHLOEM IN SUGARBEET LEAVES INFECTED WITH THE BEET CURLY TOP VIRUS

Electron microscopy of sugarbeet leaves infected with the beet curly top virus confirmed earlier findings by light microscopy that the hyperplastic phloem consists mainly of sieve elements that are more or less abnormal in structure. Some parenchyma cells and occasional companion cells may be present. The hyperplastic phloem develops in the place of normal phloem and sometimes in the adjacent ground tissue and the xylem. The sieve elements vary in shape and may be haphazardly arranged. The protoplasts of the sieve elements have the usual characteristics of this type of cell. The sieve element plastids develop from chloroplasts if the hyperplasia occurs in chloroplast-containing parenchyma cells. The cell walls have sieve areas that often are less well differentiated than those of normal sieve elements. The hyperplastic growth in the phloem of curly top diseased plants is discussed with reference to plant tumors induced by certain other plant viruses.     

Comparative Histocytology of the Petiole and the Main Pulvinus in Mimosa pudica L.

In Mimosa pudica, the main pulvinus, which brings about leafmovements, presents unusual structural characteristics in comparisonwith the petiole. Peculiar cellular features which exist inthe cortex, epidermis, parenchyma and endodermal regions includethe shape of the cells, their disposition and the location ofthe organelles. The central cylinder of the petiole is surrounded only by afew parenchyma layers whereas the central cylinder of the pulvinusforms a narrow central core enclosed in numerous cortical parenchymalayers. The phloem of the pulvinus contains collenchymatouscells towards the outside and possesses companion cells withwall ingrowths; these phloem members do not exist in the petiole.Xylem and protoxylem parenchyma cells of the petiole possesswall ingrowths which do not occur in homologous cells of thepulvinus. Moreover the pith of the pulvinus is composed of smallfibriform elements similar to the xylem fibriform elements ofthe organ. The structures observed may facilitate exchanges between cellsin the petiole and in the pulvinus. The predominant functionsof the organs relative to lateral and longitudinal transferof nutrients and conduction of stimuli are discussed. Mimosa pudica L., sensitive plant, pulvinus, ultrastructure, conduction of stimuli, leaf movement     

地黄叶和茎的解剖学及组织化学研究

采用解剖学和组织化学方法对地黄叶和茎的显微结构以及梓醇、多糖的分布进行观察研究,以明确梓醇和多糖在地黄叶和茎中的分布特征。结果显示:(1)地黄叶的上、下表皮均分布有腺毛和非腺毛,腺毛都属于头状腺毛,包括长柄和短柄的头状腺毛,两类腺毛的分泌物化学成分主要是黄酮和多糖;叶的上、下表皮上都分布有无规则型气孔,下表皮的气孔密度比上表皮的大,但气孔指数相差不大;栅栏组织由2～3层薄壁细胞构成,排列紧密,海绵组织薄壁细胞形状无规则,细胞间隙大。(2)组织化学研究表明,海绵组织中黄斑样的薄壁细胞是梓醇和多糖的贮存场所,这类薄壁细胞在叶片边缘的齿末端处最为集中,茎的皮层、韧皮部和木质部的薄壁细胞也都是梓醇和多糖的贮存场所。     

珊瑚菜植株分泌道发育和分布的解剖学观察

利用植物解剖学方法对珊瑚菜（Glehnia littoralis Fr．Schmidt ex Miq．）体内分泌道的发育和分布进行了观察。结果表明,珊瑚菜的分泌道有分枝,为溶生型,由1层分泌细胞围绕腔道而成。珊瑚菜叶片的分泌道发育较早,在幼叶阶段即发育成形。在根的次生韧皮部、根状茎的皮层和靠近初生木质部的髓部、叶脉的薄壁组织、叶柄维管束周围和厚角组织内侧的薄壁组织、花序轴正对维管束的皮层薄壁组织中以及果实的果壁维管束内外侧的薄壁组织中均分布有分泌道,分泌道在珊瑚菜体内分布广泛。     

Anatomy of the vegetative organs and secretory structures of Rhaponticum carthamoides (Asteraceae)

Roots, stems, rhizomes and leaves of Rhaponticum carthamoides (Willd.) Iljin (a Siberian adaptogenic plant, originating from the Altai and Saian Mountains) of different ages were investigated by means of light and electron microscopy. Schizogenous secretory reservoirs occurred in every organ, and were located within the secondary xylem (adventitious roots and rhizome of young plants), at the interface of endodermis/cortical parenchyma (roots and hypocotyl), along phloem and primary xylem (older rhizome), around the vascular bundles (inflorescence stem, petiole and leaf midrib veins) and along phloem (cotyledonary and leaf veins). At the interface of endodermis/inner parenchyma, secretion accumulated in the intercellular spaces prior to the formation of proper epithelial cells. The secretion as observed by transmission electron microscopy comprised three components: soluble (i.e. absent from sections; probably phenolic), insoluble and strongly osmiophilic (probably phenolic) and insoluble, moderately osmiophilic (probably lipidic). Numerous osmiophilic oil droplets, similar to the lipidic secretion inside the reservoirs, local proliferation of rough endoplasmic reticulum and numerous multivesicular bodies characterized epithelial cells in all organs. Leucoplasts (in subterranean organs) with osmiophilic inclusions and peroxisomes with crystalloid inclusions were specific for parenchyma cells. Peltate glandular hairs were formed on leaf blades.  © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society , 2004, 144 , 207–233.