The First Record of Fossil Wood of Winteraceae from the Upper Cretaceous of Antarctica

Fossil wood of the Winteraceae from the Upper Cretaceous sedimentsof James Ross Island, Antarctic Peninsula, is described herefor the first time. The specimen is characterized by the absenceof vessels, rays of two distinct sizes and tracheids with one–threerows of circular bordered pits, mainly on the radial walls,grading to horizontally elongate and scalariform. Despite anatomicalconformity to the family Winteraceae, the fossil wood is notidentical to any one extant genus and therefore has been assignedto the fossil organ genus Winteroxylon Gottwald with which thefossil shows greatest similarity. Copyright 2000 Annals of BotanyCompany Antarctica, Cretaceous, angiosperm, wood, anatomy, Winteraceae, Winteroxylon, fossil, palaeoclimate     

A New Species of Araucarioxylon Kraus from the Early Early Permian,Nei Mongol,China

A kind of silicified fossil wood with mixed pits on the radial tracheid wall is described. The fossil wood was collected from the top of Taiyuan Formation (early Early Permian) in Wuda Mining District, Nei Mongol. Compared with the Paleozoic fossil woods in the world, it is put into Araucarioxylon Kraus and named as A. laoshidanense sp. nov. Based on the character of possessing mixed pittings (alternate and opposite pittings) on the radial tracheid wall, the fossil wood is believed to be one of the unknown primitive conifers.Diagnosis of the new species: Only secondary xylem preserved and consisting of axial tracheids and rays. Growth ring boundary, resin duct and axial parenchyma absent. One to Four (commonly 2or3) seriates of bordered pits mostly alternate but sometimes opposite）on the radial tracheid wall. One to Four (commonly1, rarely2 to 4) Cupressoid pits in each cross-field. Rays usually uniseriate, sometimes partly-biseriate and 2 to 39 (mainly3-5) cells high.     

内蒙古早二叠世早期南洋杉型木属一新种

报道了一种具混合型纹孔（互列式纹孔和对列式纹孔）的化石本。化石木产自内蒙古乌达矿区老石旦矿附近太原组上部,地质时代为早二叠世早期。经比较,确认为南洋杉型木属（Ａｒａｕｃａｒｉｏｘｙｌｏｎ Ｋｒａｕｓ）一种新;老石旦南洋杉型木（Ａｒａｕｃａｒｉｏｘｙｌｏｎ ｌａｏｓｈｉｄａｎｅｎｓｅ ｓｐ．ｎｏｖ．）．根据混合型纹孔的存在及其他特征,认为新种可能代表了一种原始的松杉类植物的木材化石。主要特征：仅保存     

The Orientation and Localization of Cortical Microtubules in Differentiating Conifer Tracheids during Cell Expansion

Arrays of cortical microtubules (MTs) on radial walls in differentiatingtracheids of Taxus cuspidata were randomly oriented when primarywalls formed. The orientation of MTs changed progressively fromlongitudinal to transverse as cells expanded. During formationof primary walls, MTs in differentiating tracheids disappearedlocally at sites of future intertracheal bordered pits. In furtherdifferentiated tracheids, circular bands of MTs were observedaround the edges of developing bordered pits. (Received July 17, 1996; Accepted November 11, 1996)     

Sclerospiroxylon xinjiangensis nov. sp., a gymnospermous wood from the Kungurian (lower Permian) southern Bogda Mountains,northwestern China: Systematics and palaeoecology

A new silicified wood, Sclerospiroxylon xinjiangensis Wan, Yang et Wang nov. sp., is described from the Cisuralian (lower Permian) Hongyanchi Formation in southeast Tarlong section, Turpan City, Xinjiang Uygur Autonomous Region, northwestern China. The fossil wood is composed of pith, primary xylem and Prototaxoxylon-type secondary xylem. The pith is solid, circular, heterocellular, with sclerenchyma and parenchyma. The primary xylem is endarch to mesarch, with scalariform thickenings on tracheid walls. The secondary xylem is pycnoxylic, composed of tracheids and parenchymatous rays. Growth rings are distinct. Tracheids have mostly uniseriate, partially biseriate araucarian pitting on their radial walls. Helical thickenings are always present on both the radial and the tangential walls. Rays are 2–14 cells high, with smooth walls. There are 2 to 7, commonly 2 to 4 cupressoid pits in each cross-field. Leaf traces suggest that S. xinjiangensis nov. sp. was evergreen with a leaf retention time of at least 15 years. Based on the sedimentological evidence, growth rings within the S. xinjiangensis nov. sp. could have been caused by seasonal climatic variations, with unfavorable seasons of drought or low temperature. Low percentage of latewood in each growth ring is probably due to the intensity of climatic seasonality and/or long leaf longevity.     

Anatomy of the vessel network within and between tree rings of Fraxinus lanuginosa (Oleaceae)

The three-dimensional (3-D) arrangement of vessels and the vessel-to-vessel connections in the secondary xylem of the stem of the ring-porous hardwood tree Fraxinus lanuginosa were studied in series of thick transverse sections with epifluorescence microscope and confocal laser scanning microscope. Vessels were traced in sequential sections, and vessel networks were reconstructed in two segments of wood with dimensions of 2 × 1.4 × 21.2 mm(3) and 2 × 1.4 × 5.8 mm(3) (tangential × radial × axial). The arrangement of vessels and intervessel pits were visualized by scanning electron microscopy in low-density polyethylene microcasts and on exposed tangential faces of growth-ring boundaries. The vessels deviated from the stem axis in the tangential direction and, to a lesser extent, in the radial direction. Some neighboring vessels were twisted around each other. Vessels that appeared solitary in single sections were found to be sequentially contiguous with a number of other vessels, forming networks that extended in the tangential direction and across growth-ring boundaries. In the 21.2-mm wood block, all earlywood vessels at the growth-ring boundary made contact with latewood vessels in the previous tree ring. Within a growth ring however, only a single contact was observed between individual earlywood and latewood vessels. Densely arranged intervessel pits were characteristic in the regions where adjacent vessels made contact with each other. Such bordered pits were abundant in the tangential walls of vessel elements adjacent to growth-ring boundaries. Therefore, bordered pits appear to provide the pathway for the radial transport of water via the vessel network across growth-ring borders. Fiber-tracheids, observed as terminal cells in the tree rings, might also contribute to the apoplastic transfer of water across ring borders.     

Myosin,microtubules, and microfilaments: co-operation between cytoskeletal components during cambial cell division and secondary vascular differentiation in trees

The immunolocalisation of unconventional myosin VIII ('myosin') in the cells of the secondary vascular tissues of angiosperm (Populus tremula L. x P. tremuloides Michx. and Aesculus hippocastanum L.) and gymnosperm (Pinus pinea L.) trees is described for the first time and related to other cytoskeletal elements, as well as to callose. Both myosin and callose are located at the cell plate in dividing cambial cells, whereas actin microfilaments are found alongside the cell plate; actin and tubulin are both associated with the phragmoplast. Myosin and callose also localise to the plasmodesmata-rich pit fields in the walls of living cells, which are particularly abundant within the common walls between ray cells and between ray cells and axial parenchyma cells in the phloem and xylem. In those xylem ray cells that contact developing vessel elements and tracheids, myosin, tubulin, actin and callose are localised at the periphery of developing contact and cross-field pits; the respective antibodies also highlight the bordered pits between vessels and between tracheids. The aperture of the bordered pits, whose diameter diminishes as the over-arching border of these pits develops, also houses myosin, actin and tubulin. Myosin, actin and callose are also found together around the sieve pores of sieve elements and sieve cells. We suggest that an acto-myosin contractile system (a 'plant muscle') is present at the cell plate, the sieve pores, the plasmodesmata within the walls of long-lived parenchyma cells, and at the apertures of bordered pits during their development.     

Modelling the hydrodynamic resistance of bordered pits

Previous studies of the hydrodynamics of plant stems have shown that resistance to flow through bordered pits on the side walls of tracheids makes up a significant proportion of their total resistance, and that this proportion increases with tracheid diameter. This suggests a possible reason why tracheids with a diameter above around 100 microm have failed to evolve. This possibility has been investigated by obtaining an estimate for the resistance of a single pit, and incorporating it into analytical models of tracheid resistance and wood resistivity. The hydrodynamic resistance of the bordered pits of Tsuga canadensis was investigated using large-scale physical models. The importance of individual components of the pit were investigated by comparing the resistance of models with different pore sizes in their pit membrane, and with or without the torus and border. The estimate for the resistance of a real bordered pit was 1.70x10(15) Pa s m(-3). Resistance of pits varied with morphology as might be predicted; the resistance was inversely proportional to the pore size to the power of 0.715; removing the torus reduced resistance by 28%, while removal of the torus and border together reduced it by 72%. It was estimated that in a 'typical tracheid' pit resistance should account for 29% of the total. Incorporating the results into the model for the resistivity of wood showed that resistivity should fall as tracheid diameter increases. However, to minimize resistance wider tracheids would also need to be proportionally much longer. It is suggested that the diameter of tracheids in conifers is limited by upper limits to cell length or cell volume. This limitation is avoided by angiosperms because they can digest away the ends of their cells to produce long, wide vessels composed of many short cells.     

Discovery of vessels in Tetracentron (Trochodendraceae) and its systematic significance

Through SEM observation, we found that there are vessels as well as tracheids in the secondary wood of Tetracentron sinense Oliv. The vessel elements are as narrow and as long as or slightly shorter than the tracheids and generally have 1 to 3 very long, or sometimes relatively short and oblique end-wall perforation plates; such perforation plates are also present on the lateralwalls. The perforation plates of the vessels include scalariform and reticulate-scalariform types, with various degrees of membrane remnants present in the end walls.     

Anatomical features that facilitate radial flow across growth rings and from xylem to cambium in Cryptomeria japonica

Background and Aims

Although the lateral movement of water and gas in tree stems is an important issue for understanding tree physiology, as well as for the development of wood preservation technologies, little is known about the vascular pathways for radial flow. The aim of the current study was to understand the occurrence and the structure of anatomical features of sugi (Cryptomeria japonica) wood including the tracheid networks, and area fractions of intertracheary pits, tangential walls of ray cells and radial intercellular spaces that may be related to the radial permeability (conductivity) of the xylem.

Methods

Wood structure was investigated by light microscopy and scanning electron microscopy of traditional wood anatomical preparations and by a new method of exposed tangential faces of growth-ring boundaries.

Key Results

Radial wall pitting and radial grain in earlywood and tangential wall pitting in latewood provide a direct connection between subsequent tangential layers of tracheids. Bordered pit pairs occur frequently between earlywood and latewood tracheids on both sides of a growth-ring boundary. In the tangential face of the xylem at the interface with the cambium, the area fraction of intertracheary pit membranes is similar to that of rays (2·8 % and 2·9 %, respectively). The intercellular spaces of rays are continuous across growth-ring boundaries. In the samples, the mean cross-sectional area of individual radial intercellular spaces was 1·2 µm² and their total volume was 0·06 % of that of the xylem and 2·07 % of the volume of rays.

Conclusions

A tracheid network can provide lateral apoplastic transport of substances in the secondary xylem of sugi. The intertracheid pits in growth-ring boundaries can be considered an important pathway, distinct from that of the rays, for transport of water across growth rings and from xylem to cambium.Key words: Cryptomeria japonica, bordered pit, intercellular spaces, lateral transport, tracheid network, water conduction, xylem permeability     

Characteristics of Wood Structure in Gymnosperms and Their systematic Significance

The systematic positions and taxonomic ranks of orders and families in Gymnosperms, especially those in Coniferopsida, are analysed and discussed in this paper based on the evolutionary trends in the wood structure. The opinions of the present authors are as follow: 1. The separation of the Araucariaceae from the Coniferae and establishment of the Araucariales are reasonable,because the intertracheid pitting in the wood is the Araucarioid type and there are no pits on both horizontal and end walls of ray parenchyma cells in the family. 2. The position of the genus Ginkgo in Cheng’s system is acceptable. Ginkgo is more similar to Coniferae than to Cycadaceae in the wood structure. 3. According to the characteristics of wood structure, arrangement of the Podocarpaceae, Cephalotaxaceae and Taxaceae between the Araucariaceae and the Pinaceae is reasonable. Among these families, the Cephalotaxaceae and Taxaceae are more closely related to each other in the view of the spiral thickenings which often appear on the inner wall of wood tracheids. 4. Further evidence for the establishment of the Sciadopitysaceae is provided. For example, most of cross-field pits in the wood of the Sciadopitysaceae are window like, while some of them are of the Lemon type or the Subtaxodioid type; bordered pits are of the Araucaria B type. 5. The characteristics of wood structure in the genus Platycladus differ greatly from Thuja. The former has cross field pits of the Cupressoid type, bordered pits of Araucaria B type and warty layer on the inner surface of tracheids. All of these characteristics have added further evidence for the separation of Platycladus from Thuja. 6. Based on the structural characteristics of woody rays in the Pinaceae, the most primitive genera are Abies, Keteleeria and Pseudolarix, while more advanced ones are Cedrus and Tsuga, and even more advanced ones are Pseudotsuga, Cathaya, Picea and Larix, all of which share normal resin canals. The most advanced genus is Pinus which is also of normal resin canals. Pinus can be divided into three subgenera, Haploxylon, Parry and Diploxylon, according to the presence or absence of dentation and warty layer in wood tracheids. 7. It is reasonable to place the genus Amentotaxus in the Taxaceae, because membrane of bordered pits in the genus is similar to that in the other four genera of the Taxaceae, both of the Araucaria type. 8. The present authors agree with Cheng’s (1978) treatment of Sect. Heopeuce in Tsuga, based on the fact that Tsuga longibracteata has traumatic resin canals and warty layer. Reducing Pinus hwangshanensis into P. taiwanensis, made by Cheng, is reasonable because of the similarities between P. hwangshanensis and P. taiwanensis in the wood structure. The establishment of a new subgenus, Patty, for Pinus bungeana is suitable based on chemotaxonomy, morphology and the distinct warty layer on the innersurface of wood tracheids.     

水青树特殊管胞的分布位置及其形态特征的研究

针对水青树（Tetracentron sinense）中一类特殊管胞进行较为全面的观察研究,判断细胞种类并分析维管组织输导机理及树木进化过程中的细胞演化规律。通过切片和解离技术,借助光学显微镜和电子显微镜对34年生水青树特殊管胞的分布位置和形态特征进行观察。结果表明：(1)特殊管胞在树木水平方向自内向外径向呈串排列,并贯穿年轮界限,多为一列,少数两列,且较为稀见。每个特殊管胞弦向左右两侧或单侧均与木射线细胞相连通。纵向上,特殊管胞单独或数个上下端接相连。(2)特殊管胞主要有以下3种类型：无端壁的纺锤形,有一个倾斜端壁,以及有两个倾斜端壁。特殊管胞的平均长度为286.44μm;横切面为四边形,平均弦向宽度为55.22μm,其平均壁厚为1.53μm。(3)特殊管胞两端封闭,无穿孔。(4)特殊管胞侧面壁上的纹孔数量较多且纹孔膜明显可见,具体表现为：弦面壁上布满特殊管胞之间的具缘纹孔,呈对列、互列偶见梯状排列;径面壁上存在与射线细胞间的具狭缘单纹孔,呈大圆形至椭圆形,每区域多为2～10个纹孔,呈1～4排横列;径面壁上与正常管胞间几无纹孔。水青树特殊管胞分布有一定规律,其长度远小于水青树正常管胞...     

Ecpagloxylon mathiesenii gen. nov. et sp. nov., a Jurassic wood from Greenland with several primitive angiosperm features

Fossil wood specimens from the late Early–early Middle Jurassic of Jameson Land, Eastern Greenland, have several unexpected features: tracheids of irregular size and shape, thinly pitted ray cell walls, heterogeneous rays, partially scalariform radial pitting, both areolate and simple pits, and pitted elements associated with rays. These characters diverge markedly from those typical of Jurassic wood, which usually conform to those of modern conifers. Although this combination of features is not encountered in any extant angiosperm, each has been documented in one or several extant homoxylous angiosperms, particularly Amborella, Trochodendron, and Tetracentron. As these wood specimens are not found in connection with any reproductive part, it is impossible to confidently assign them to the angiosperms. If a Jurassic angiosperm did exist, however, it might well have had a similar wood. This material is an early bench-mark in the evolution that led from homoxylous conifer-like wood to that of the angiosperms. Its particular biogeography (Arctic) could renew the discussion about the area of origin of the angiosperms.     

Arrangement of cortical microtubules during formation of bordered pit in the tracheids ofTaxus

Summary The arrangement of cortical microtubules during the development of the secondary wall and bordered pits in the tracheids ofTaxus was examined by immunofluorescence and electron microscopy. The cambial region of radial longitudinal sections of developing young shoots (2–3 years old) contains cells at various stages of differentiation from cambial cells to tracheids. At the early stage of formation of bordered pits, circular bands of microtubules were seen to be associated with the inner edge of the border of the developing pit. In other regions than the pit secondary wall of uniform thickness was laid down, and obliquely oriented cortical microtubules ran parallel to one another. These cortical microtubules also covered the surface of the border of the developing pit on the side facing the center of the cell. As the border of the pit developed, a circular band of MTs remained associated with the inner edge of border, suggesting that the MTs were involved in the formation of the rim of the bordered pit, extending the initial border thickening, which consisted of concentrically oriented cellulose microfibrils. After completion of the formation of the bordered pit, helical thickenings became apparent. The obliquely oriented microtubules were organized in bands parallel to one another, being superimposed on the helical thickenings. The involvement of MTs in the formation of bordered pits and helical thickening is discussed.     

FLORA OF THE LOWER CRETACEOUS CEDAR MOUNTAIN FORMATION OF UTAH AND COLORADO. PART III: ICACINOXYLON PITTIENSE N. SP

Icacinoxylon pittiense, a new species of angiospermous wood from the Lower Cretaceous Cedar Mountain Formation of Utah is described and compared with similar fossil and modem woods. It is distinguished from other species of Icacinoxylon by its thick-walled fiber-tracheids with their walls making up at least 50% of the total diameter of the cells, conspicuous bordered pits with obliquely crossing extended apertures on both the tangential and radial walls of its fiber-tracheids, scalariform perforation plates with as few as four or greater than 30 bars, transitional opposite to scalariform pitting on its vessel walls, thick-walled ray cells, and distinct sheath or border cells in its rays. Icacinoxylon pittiense is the first species of this genus to be reported from Cretaceous sediments. This wood is of special interest because very few angiosperm woods have been reported from lower Cretaceous strata.     

Bordered pit structure and function determine spatial patterns of air-seeding thresholds in xylem of Douglas-fir (Pseudotsuga menziesii; Pinaceae) trees

The air-seeding hypothesis predicts that xylem embolism resistance is linked directly to bordered pit functioning. We tested this prediction in trunks, roots, and branches at different vertical and radial locations in young and old trees of Pseudotsuga menziesii. Dimensions of bordered pits were measured from light and scanning electron micrographs, and physiological data were from published values. Consistent with observations, calculations showed that earlywood tracheids were more resistant to embolism than latewood tracheids, mainly from earlywood having stretchier pit membranes that can distend and cover the pit aperture. Air seeding that occurs in earlywood appears to happen through gaps between the torus edge and pit border, as shown by the similar calculated pressures required to stretch the membrane over the pit aperture and to cause embolism. Although bordered pit functioning was correlated with tracheid hydraulic diameter, pit pore size and above all pit aperture constrained conductivity the most. From roots to branches and from the trunk base to higher on the trunk, hydraulic resistance of the earlywood pit membrane increased significantly because of a decrease in the size of the pit aperture and size and number of margo pores. Moreover, overall wood conductivity decreased, in part due to lower pit conductivity and a decrease in size and frequency of pits. Structural and functional constraints leading to the trade-off of efficiency against safety of water transport were also demonstrated at the individual pit level, with a positive correlation between pit membrane resistance on an area basis and the pressure differential required to cause membrane stretching, a characteristic that is essential for pit aspiration.     

The vestured pits of Eucalyptus regnans F. Muell.: a study using scanning electron microscopy

Scanning electron microscopy has been used to examine the surface architecture, before and after various chemical treatments, of the pits in the walls of vessels, vasicentric and fibre tracheids, and parenchyma cells, which together make up the wood of Eucalyptus regnans. The treatments included water at 150°C under pressure, hydrofluoric acid, delignifying agents and potassium permanganate. All bordered pits were vestured; half-bordered pits were vestured, partially vestured or non-vestured. No distinction could be made between warts and vestures on morphological or chemical grounds. An hypothesis is advanced which relates vesture formation to prolongation of the activity of the protoplast in pits as the cells die. Vestures, on the basis of this hypothesis, could be regarded as enlarged or conglomerate warts.     

STRUCTURE OF TRACHEIDS IN THREE SPECIES OF LYCOPODIUM

The structure of tracheids in Lycopodium lucidulum, L. clavatum, and L. tristachyum was studied with the light microscope. Protoxylem development is at least sometimes and possibly always mesarch in indeterminate axes of all three species. Centrifugally formed protoxylem elements are reticulate and discontinuities in the secondary walls of these elements are sometimes conspicuously bordered. Wall thickenings of first formed protoxylem elements consist mainly of indirectly connected rings. Late centripetally formed protoxylem elements and transitional elements have a reticulate secondary wall pattern. The narrowest metaxylem elements have circular bordered pits while in wider metaxylem elements pits are bordered and may vary from circular to scalariform. Pitting is uniseriate to triseriate in tracheids of all three species, and intermittent tetraseriate pitting was occasionally observed in L. lucidulum. Crassulae occur in tracheids of the three species, and in L. clavatum an additional framework, probably representing thickened compound middle lamella, is also present. Pits often appear helically arranged, and in all three species pits are connected by thin areas in the secondary wall. Macrofibrils approximately 0.5 μ wide were observed in tracheids of the three species. In L. clavatum the arrangement of macro-fibrils was predominantly bidirectional.     

Modelling the hyphal growth of the wood-decay fungus Physisporinus vitreus

The white-rot fungus, Physisporinus vitreus, degrades the membranes of bordered pits in tracheids and consequently increases the permeability of wood, which is a process that can be used by the wood industry to improve the uptake of wood preservatives and environmentally benign wood modification substances to enhance the use and sustainability of native conifer wood species. To understand and apply this process requires an understanding of how a complex system (fungus-wood) interacts under defined conditions. We present a three-dimensional fungal growth model (FGM) of the hyphal growth of P. vitreus in the heartwood of Norway spruce. The model considers hyphae and nutrients as discrete structures and links the microscopic interactions between fungus and wood (e.g. degradation rate and degree of opening of pits) with macroscopic system properties, such penetration depth of the fungus, biomass, and distribution of destroyed pits in early- and latewood. Simulations were compared with experimental data. The growth of P. vitreus is characterized by a stepwise capture of the substrate and the effect of this on wood according to different model parameters is discussed.