Pit Aperture Research Articles

SEM Studies on Vessels of the Homophyllous Species of Selaginella

Metaxylem vessel elements from macerated xylem of rhizomes and rhizophores of Selaginella arizonica, Selaginella bigelovii, and Selaginella oregana were examined with scanning electron microscopy (SEM). All species have transverse to somewhat oblique simple perforation plates on end walls of vessels; presence of tracheids could not be determined with SEM. Lateral walls possess scalariform pitting except for S. bigelovii, in which pitting is opposite. Pit membranes are generally intact, but pits on some areas of lateral walls contain remnants of pit membranes; these remnants chiefly take the form of strands or threads that traverse the pit apertures. Areas of pits with such porose pit membranes may be regarded as incipient perforation plates, like lateral perforation plates or incipient perforation plates we have reported in ferns. These lateral perforation plates, as well as the simple end wall perforation plates, may aid in rapid uptake of water during short periods when water is available; studies on water uptake patterns of homophyllous Selaginella species are needed to examine this possibility.

CALLITROID (CALLITRISOID) THICKENING IN CALLITRIS

In softwood tracheids, callitroid thickening is the term given to raised bars located above and below individual bordered pit apertures. Although most well developed in the Australasian genus Callitris, callitroid thickening is reported to be absent from six Callitris species and to vary in its frequency and prominence. An SEM study of callitroid thickening was carried out on multiple wood samples of each Callitris species, taken from trees growing in the wild. The aims of the study were to determine the occurrence, frequency, visual prominence and morphology of callitroid thickening in all Callitris species and to determine whether it could be used taxonomically. Callitroid thickening was found in all (19) species of the genus, in contrast to previous reports of its absence in some species. In general, callitroid thickening occurred at higher frequencies and was more prominent in species from dry habitats than in those from wet habitats. The frequency of thickening varied between and within samples and, for example, it was always more frequent on pits in narrow rather than in wide tracheids. Callitroid thickening varied in its morphology, and types consisting of one to four bars, extending completely or only partially across the inner radial wall of the tracheid, were observed. Thickening on tracheid-ray pits within cross fields occurred in all species, and with similar frequency and morphology to thickening of bordered pits. Our findings suggest that frequency of callitroid thickening is useful taxonomically in separating four groups of Callitris species and in assisting in the identification of certain individual species.

木質材料 遠心力場における針葉樹林の壁孔壁の挙動

The behavior of pit membrane was examined from the dehydration process under the centrifugal field. According to this method, an arbitrary pressure difference (water potential by the centrifuge) is obtained by the rotational speed and the distance inward the dehydration surface. The pressure differential required to close the pit aperture by the pit membrane was evaluated as the range from 0.119MPa to 0.178MPa for sapwood of Sugi. The portion treated by the pressure differential of 0.252MPa was easier to dehydrate and it was estimated that the pit membranes in sapwood were broken by the pressure differential of 0.332MPa. The SEM observation showed the breaks of the pit membrane.The pressure differential up to 1.32MPa did not make the pit membrane in heartwood break.The centrifugal method was possible to determine the pressure differential that produces the pit aspiration and the break of pit membrane in sapwood of softwood.

Growth Rate Effects on Intra-Ring and Inter-Ring Trajectories of Microfibril Angle in Norway Spruce (Picea Abies)

Fourteen Norway spruces [Picea abies (L.) Karst.], randomly sampled as 7 fast-grown and 7 slow-grown trees, were used to test whether an increased tree growth rate in circumference affects the intra-ring and inter-ring trajectories of the microfibril angle in the S2 layer of the tracheid wall. Those trajectories describe the fluctuations of the S2 microfibril angle, respectively, from earlywood to latewood within rings and from pith to bark among rings. Using the cross-field pit apertures, intra-ring measures of microfibril angle were made at 11 equally-spaced sampling sites over each of 8 growth rings, following an 11 × 8 doubly repeated measures design with the tree as the 'subject' on which repeated measures were made. All the intra-ring trajectories of microfibril angle decreased linearly from earlywood to latewood, whereas the inter-ring trajectories showed significant year effects. Both types of trajectories are significantly affected by the growth rate after first thinning, as the fast-grown spruces showed a systematically larger microfibril angle and a mean microfibril angle of 290 compared to 21 0 for the slow-grown spruces. Thus, lower tensile and tear strengths of tracheids as well as some modifications of the mechanical properties of solid wood and paper can be expected from Norway spruces growing faster than 2.2 cm/year in circumference.

Origins and nature of vessels in monocotyledons. 2. Juncaginaceae and Scheuchzeriaceae

SEM studies of roots and rhizomes of Triglochin (one species) and Maundia (monotypic) of Juncaginaceae and the sole species of Scheuchzeriaceae, Scheuchzeria palustris, reveals that vessels are present not only in roots, as previously reported, but also in rhizomes. The perforations contain pit membranes with pores of various sizes. Striate pit membranes, like those previously seen in Acorus, occur on pit remnants in peforations and on pit membranes of lateral walls in all genera studied. Grooves interconnecting pit apertures are illustrated for root tracheary elements of Triglochin; this is believed to be a first report of this feature for monocotyledons. The tracheary elements of Juncaginaceae and Scheuchzeriaceae are similar in their thick walls and narrow slitlike pits, lending support to the close relationship between the two families often claimed.

Wood anatomy of the dicotyledons indigenous to New Zealand 26. Rutaceae*

Wood anatomy of Melicope ternata, M. simplex, and Phebalium nudum is described. In M. simplex and M. ternata vessels have no helical thickenings, most perforation plates are simple but some are scalariform or reticulate, grooves connect pit apertures, and vessel to ray pits are sometimes unilaterally compound. Disjunctive ray and axial parenchyma cells are present. Melicope simplex is distinguished from M. ternata in having narrower rays, more disjunctive ray cells, and narrower boundary bands of axial parenchyma. The vessel elements of P. nudum have helical thickenings and simple perforation plates, and lack unilaterally compound pits. Disjunctive axial parenchyma cells are absent and disjunctive ray cells are rare. Boundary axial parenchyma and rays are usually only 1-2 cells wide. Vasicentric tracheids are common in P. nudum but rare in M. simplex and M. ternata. Silica bodies occur in the parenchyma cells of all three species.

SEM studies on vessels in ferns. 2. Pteridium

Xylem from roots and rhizomes of two infraspecific taxa of Pteridium aquilinum was studied by means of scanning electron microscopy (SEM). All tracheary elements proved to be vessels. End wall perforation plates were all scalariform, lacked pit membrane remnants in at least the central part of the perforation plate, and varied with respect to width of bars, from wide to tenuous, and with respect to presence of pit membrane remnants. In addition, porose pit membranes on walls that are likely all lateral vessel-to-vessel walls must be considered to be perforations also, although different from those on end walls. Lateral wall perforation plates, hypothesized by one worker on the basis of tylosis presence but denied by another on the basis of light microscopy, were confirmed by demonstration of pores with SEM. In addition, lateral walls of Pteridium vessels bear some grooves interconnecting pit apertures; this feature is newly figured by SEM for ferns. Lateral wall pitting that is not porose may either have striate thickenings of the primary wall or be smooth. Vessel presence and degree of specialization in Pteridium vessels may bear a relationship to the wide ecological tolerances of the genus.

Comparison of wood decay among diverse lignicolous fungi

In decay tests with 98 isolates (78 species) of lignicolous fungi followed by chemical and anatomical analyses, the validity of the generally accepted, major decay types (white, brown, and soft rot) was confirmed, and no new major types proposed. We could distinguish soft rot from other decay types based on anatomical and chemical criteria, without reliance on cavities or recourse to taxonomy of causal agents. Chemically, soft rot of birch could be distinguished from white rot by lower Klason lignin loss, and from brown rot by much lower alkali solubility. Anatomically, erosion of birch fiber walls in soft rot was distinguished from that in white rot by the angular erosion channels, V-shaped notches and diamond-shaped, eroded pit apertures that predominated in the former and their rounded forms in the latter.Substantial decay was caused by fungi representing eight orders in addition to the Aphyllophorales. Members of the Exidiaceae generally caused low weight losses and anatomical and chemical patterns of degradation characteristic of white rot. Isolates of Auricularia auricula-judae also caused a white rot, with high weight losses and unusual, branching microcavities that were oriented longitudinally in the S2 cell-wall layer. Ten species of the Dacrymycetales caused a brown rot like that caused by some Aphyllophorales; most caused high weight losses.Among white-rot fungi on birch, a relationship was observed between strongly selective delignification and strongly selective utilization of mannose. Among brown-rot fungi on birch, the top two polyose sugars (not including glucose) in order of selectivity were galactose>mannose; among soft-rotters they were arabinose>xylose. On pine, distinctions were not so clear, but some differing trends were evident.Previously unreported selective delignifiers were found in the Auriculariales, Agaricales, and in two orders of gasteromycetes. Selective delignification was most pronounced at low weight losses. Certain decay features similar to those in the Ascomycota were found in the Auriculariales, consistent with hypotheses that place that order near the phylogenetic root of Basidiomycota. A sequence of origins of decay types is proposed.

Tem Study of Wound-Induced Vessel Occlusions in European Ash (Fraxinus Excelsior L.)

Vessel occlusions in branches of Fraxinus excelsior L. were investigated by means of transmission electron microscopy. The vessel occlusions are formed by exudates released from adjacent ray and axial parenchyma cells through the intact pit membranes. Initial stages mostly display balloon- like structures protruding from the pit aperture into the vessellumen. These inclusions possess a very electron dense outer membrane and dispersed exudates in their interior. Therefore, the vessel occlusions in F. excelsior do not represent true tyloses.

Secondary growth and wood histology of Welwitschia

New observations regarding secondary growth and vascular tissues in Welwitschia are based on roots (used because of the longitudinal orientation of most vascular tissues). Welwitschia has successive cambia that produce xylem and phloem. Contrary to previous reports, the cambia produce secondary phloem with phloem rays and secondary xylem that has readily definable xylem rays and axial parenchyma. Internal sculpturing (grooves associated with pit apertures) of tracheary elements is figured with SEM; observations confirm the descriptions of Bierhorst (1960) . Tori and vesturing are apparently absent on pits of tracheary elements. Abundance of gelatinous secondary walls may be related to water economy to a minor extent. A feature recently reported for Ephedra wood is newly reported for xylem rays, phloem rays and conjunctive tissue of Welwitschia : presence of minute calcium oxalate crystals lining intercellular spaces. This feature is apparently limited to the two genera. The ontogenetic origin of vascular strands added by secondary activity can be traced to phelloderm. In this feature, Welwitschia differs from Gnetum , in which the ultimate origin of new cambia can be traced to cortical tissues.

Wood Anatomy of Berberidaceae: Ecological and Phylogenetic Considerations

Qualitative and quantitative data are presented for 21 collections of Berberis and one each of Epimedium, Jeffersonia, and Nandina. Most species of Berberis have large numbers of narrow vessels ~ixed with vasicentric tracheids. Scalariform perforation plates are reported here only for Epimedium, m wh1ch they are occasional. Berberidaceae have living fibers (Berberis), fiber-tracheids plus living fibers (Nandina), or tracheids (Jeffersonia) as imperforate tracheary elements. Axial parenchyma is reported here for Jeffersonia and one species of Berberis. Previous reports of axial parenchyma in Berberis and Nandina likely refer to undivided living fibers, mostly intermixed with vessels, which are slightly shorter and with thinner walls and larger pit apertures than living fibers elsewhere in the wood. Woods of Berberis and other Berberidaceae are remarkably xeromorphic. The wide, tall rays of Berbendaceae, other than Jeffersonia, resemble rays of Clematis (Ranunculaceae) and other Ranunculiflorae. In dimensions, these rays suggest herbaceousness, but abundance of procumbent cells in these rays is not juvenilistic. No consistent differences in wood separate the subgenera Berberis and Mahonia of Berberis: although the two subgenera differ modally in several respects. Wood anatomy of Nandma IS very similar to that of Berberis, and segregation of Nandinaceae is unwarranted on the basis of wood anatomy.

Adsorption of polyethylenimine onto cellulose fibers

The adsorption of a low and a high molecular weight polyethylenimine (PEI) onto pulp fibers has been investigated. These two cases represent two extreme modes of behavior: low molecular weight PEI can penetrate into the porous wall of the fibers, while for high molecular weight PEI adsorption in pores is negligible. From both equilibrium isotherms and the kinetics of adsorption it can be concluded that PEI molecules adsorbed on the surface maintain their identity as individual molecules and do not form a uniform adsorption layer. The final coverage depends on the size of a PEI molecule in solution, which, besides the molecular weight, is determined by the ionic strength, pH and PEI concentration. The kinetics of high molecular weight PEI adsorption closely follow Smoluchowski and Langmuir kinetics, similar to the deposition of colloidal particles. Adsorption on the wall of the lumen (hollow space inside the fiber) is determined by diffusion through pit apertures and cut ends of the fibers. The kinetics of low molecular weight PEI are mainly governed by the rate at which molecules can diffuse into the pores of the fiber wall. After a few days, a pseudo-equilibrium is established in which the rate of adsorption equals the rate of desorption. The rate of PEI rearrangement is much slower than the rate of desorption. The implications of these findings to papermaking are discussed.

Wood and Bark Anatomy of Argemone (Papaveraceae)

Wood anatomy of Argemone fruticosa, sole shrubby species of the genus, is distinctive in having growth rings, thick-walled libriform fibres, thick-walled ray cells with large intercellular spaces, vessels with grooves interconnecting pit apertures, and restriction of vessels to central portions of fascicular areas. Most of these features are related to the xeric ecology of this species. Argemone turnerae is an herbaceous perennial with large roots and sterns, the wood of which exhibits features distinctively related to this habit, including succulence (axial parenchyma substitutes for libriform fibres). Both species of Argemone share such features as storied wood structure and absence of uniseriate rays, which are infrequent in dicotyledons at large but common in other Papaveraceae. Wood data are not decisive in indicating whether the ancestors of Argemone or Papaveraceae were woody or herbaceous, but several features indicative of paedomorphosis can be found in the wood. Bark of Argemone is briefly described.

The Occurrence and Morphology of Tyloses and Gums in the Vessels of Japanese Hardwoods

The occurrence and morphology of natural tyloses and gums in the vessels of 50 Japanese hardwoods (15 ring-, 34 diffuseand 1 radial-porous woods) were investigated using SEM. Tyloses were present exclusively or predominantly in 23 species (12 ring-, 10 diffuse- and 1 radial-porous woods) and gums in 15 species (3 ring- and 12 diffuse-porous woods). In the pore zones of most of the ringporous woods both tyloses and gums first occurred in an earlier ring number from the bark than in the diffNse- and radial-porous woods. Tyloses and gums originated from both ray and axial parenchyma cells in most species which have pit pairs connecting these cells to the vessels. Except for four species, the maximum and minimum diameters of the inner pit aperture from vessels to parenchyma cells were greater than 5 and 2 µm, respectively, in those species with tyloses, whereas the diameters were less than these values in species having gums. The forms of tylosis blockings in heartwood vessels were closely related to parenchyma patterns.

Regeneration of Haller's sensory organ in the tick Ixodes ricinus L.

Amputation of legs in nymphs of ticks, obtained from the first laboratory generation, resulted in regeneration of the legs after moulting to adults. Haller's sensory organ on the upper surface of each foreleg tarsus was significantly modified following regeneration. Haller's organ in non-amputated legs of the experimental ticks remained unchanged, being comparable to controls. Pored olfactory sensilla in the anterior pit, in a capsule and on a distal knoll usually increased in number, as well as grooved, thin and conical sensilla. Bordering gustatory and double-walled postcapsular sensilla either decreased or increased in number. All additional sensilla were consistent in their location. Form of the anterior pit and capsule's aperture also deeply changed after the regeneration. The authors distinguish this changes as atavistic. No correlation between changes in different parts of the organ were found. A phenomenon of induction was discovered in our study: if a distal part of tick's gnathosoma was amputated together with the left foreleg, Haller's organ in the right, untreated leg possessed the same changes after moulting as the regenerated organ in the previously amputated left foreleg.

Soleredera rhizomorpha gen. et sp. nov., a Permineralized Monocotyledon from the Middle Eocene Princeton Chert of British Columbia, Canada

Small permineralized monocotyledonous rhizomes and aerial stems from the Middle Eocene Princeton chert in British Columbia are described and named Soleredera rhizomorpha gen. et sp. nov. Rhizomes are up to 1.3 cm wide, have a narrow cortex without vascular bundles, and show a central cylinder composed of three or more irregular cycles of primary vascular bundles embedded in compact thick-walled ground tissue. The central cylinder surrounds a hollow or sometimes solid pith and is separated from the cortex by an endodermoid layer. Rhizome vascular bundles are collateral or amphivasal and lack a fibrous bundle sheath. Metaxylem consists of angular tracheids 9-42 μm wide with scalariform, transitional, opposite, or mostly alternate intervascular pitting. Pit apertures are lined with vesture-like projections. Attached to the rhizomes are lateral branches 2-3 mm wide and roots 0.5-1.5 mm wide. Aerial stems differ from the rhizomes in having two to three cycles of collateral bundles, tracheids with mostly scalariform lateral wall pitting, and ground tissue with relatively large intercellular spaces. Also, the aerial stems lack an endodermoid layer, cortex, and roots. Anatomical comparisons to extant monocotyledons show that the stems closely resemble several lilialean families (Liliaceae, Iridaceae), but lack of leaves and floral parts of Soleredera precludes its assignment to a family. Nevertheless, these vegetative remains are the first anatomically preserved lilialean megafossils from Middle Eocene deposits in North America to be described. Discovery of Soleredera adds to our knowledge of vegetative anatomy, morphology, and diversity of monocotyledons in the early Tertiary of western North America.

XYLEM ANATOMY AND HYDRAULIC CONDUCTANCE OF COSTA RICAN BLECHNUM FERNS

Hydraulic conductivities of stems, stipes, and elongate leaf stipes were determined for greenhouse‐grown Blechnum (B. fraxineum, B. fragile, B. buchtienii, B. sprucei) and Salpichlaena (S. volubilis) plants collected in tropical rain forests of Costa Rica. Organ conductivity was examined in relation to morphology and tracheid characteristics in order to gain an understanding of factors influencing water flow. Hydraulic conductivity of plant organs was determined by measurement of transpiration rates, leaf areas, and water potential gradients. Erect stemmed species develop larger whole plant water potential gradients than elongate stemmed species for a similar transpiration rate. Elongate leaves develop even smaller water potential gradients for a given transpiration rate. Stems have larger hydraulic conductivities but smaller leaf‐specific conductivities (LSCs) than stipes. Small conductivities and small LSCs are associated with short, erect stems. Elongate structures have large conductivities and large LSCs. Of the tracheid characteristics examined, the most important characteristics determining the magnitude of organ hydraulic conductivity are diameter, pit aperture area between tracheids, taper length, and cell length. Large conductivities of S. volubilis climbing leaf stipes are associated with very large‐diameter tracheids (some > 200 μm), large tracheid number, exceptionally long tracheids (some > 4 cm), large pit aperture area between tracheids, short tracheid taper, and smooth tracheid lumen walls. Hagen‐Poiseuille estimates of hydraulic conductivity range from 1.1 to 3.3 times the measured values. Conductivity of stipes is highly correlated with leaf area supplied by stipes. Conductivities of stems and elongate leaf stipes also correlate with leaf area supplied by these structures. Estimated hydraulic conductivities of field‐grown Blechnum and Salpichlaena demonstrate that larger conductivities are associated with larger plants. This study contributes toward our knowledge of fern water relations and extends previous growth form/hydraulic architecture characterizations by providing a more comprehensive comparison of closely related species. In addition, this study provides evidence for the relative importance of tracheid characteristics in determining the magnitude of organ hydraulic conductivity.

Water‐stress‐induced xylem embolism in three species of conifers

Abstract. The mechanism of water‐stress‐induced xylem embolism was studied in three species of conifers: Abies balsamea (L.) Mill., Picca rubens Sarg, and Juniperus virginiana L. Each species showed a characteristic relationship between xylem tension and the loss of hydraulic conductivity by air embolism. Abics balsamea and Picca rubens began to embolize at tensions between 2 and 3 MPa and were completely non‐conducting between 3 and 4 MPa. Juniperus virginiana was least vulnerable, beginning to embolize at 4 and still retaining approximately 10% conductivity at 10 MPa. As with a previous study of the vessel‐bearing Accr saccharum Marsh., a brief perfusion of branch segments with an oxalic acid and calcium solution (10 and 0.1 mol m−3. respectively) increased the vulnerability of the xylem to embolism; this was especially pronounced in Abies balsamea. In order to test whether embolism was caused by aspiration of air into functional tracheids from neighbouring embolized, ones (the ‘air‐seeding’hypothesis), hydrated branch segments were injected with air at various pressures and measured for embolism. Results supported the air‐seeding hypothesis because the relationship between injection pressure and embolism for both native and oxalic‐calcium‐treated segments was essentially the same as for embolism induced by xylem tension. Structural and experimental evidence suggested the air seeding occurred through inter‐tracheid pit membranes when the thickened torus region of the membrane became displaced from its normal sealing position over the pit aperture. Thus, the embolism‐inducing tension may be a function of pit membrane flexibility. This tension is of ecological significance because it reflects to some extent the range of xylem tensions to which a species is adapted.

Torus Structure and Development in Species of Daphne

A torus is present in intervascular pit membranes in the wood of Daphne odora and D. cneorum, but not in D. mezereum. In the two former species, each torus is surrounded by a margo consisting of fibrillar material in a tightly woven pattern. Tori are of greater diameter than pit apertures and completely occlude the apertures during aspiration. Evidence from D. odora indicates that torus deposition is spatially associated with vesicles and a plexus of microtubules, and does not begin until pit border formation is complete. The material deposited during torus synthesis also impregnates the wall of the pre-existing pit membrane. The plasmalemma often is closely appressed to the pit membrane at the site of the developing torus. In half-bordered pit pairs between tracheary elements and parenchyma cells, a torus thickening is deposited only on the side of the tracheary element. As in Osmanthus americanus, it is hypothesised that the presence of tori in species of Daphne prevents rupture of the pit membrane during aspiration.

Vessel Occlusions in Plants: Morphological, Functional and Evolutionary Aspects

The minimum pit aperture diameter of a vessel-parenchyma pit pair was found as the decisive wood anatomical feature for vessel occlusion by either tyloses or gums. Based on this observation, as well as on considerations and established knowledge about the functional significance of vessel occlusions, an evolutionary hypothesis is presented. In order to withstand microorganisms and embolisms, plants are able to occlude their vessels with tyloses or gums. The most primitive Angiosperms show tylosis formation. With the decreasing pit sizes in the vessel wall during plant evolution, gum formation was developed, whereas the increasing vessel sizes led in some plants to renewed tylosis formation.