扁圆封印木（相似种）茎干的解剖特征

贵州省水城矿区晚二叠世煤核中扁圆封印木（相似种Ｓｉｇｉｌｌａｒｉａ ｃｆ．ｂｒａｒｄｉｉＢｒｏｎｇｎ．）茎干的主要解剖特征如下：管状中柱,具多边形薄壁细胞组成的髓。初生木质部成环带状,外缘呈规则的齿槽状,向心式发育。次生木质部显束状特征,横切面管胞为方圆至长方形,纵切面为梯状壁增厚,并具流苏纹。射线１—２列细胞宽,数个至十余个细胞高。叶迹起源于初生木质部外缘的槽中,中始式,但以向心发育为主。     

STRUCTURALLY PRESERVED FOSSIL PLANTS FROM ANTARCTICA. I. ANTARCTICYCAS,GEN. NOV., A TRIASSIC CYCAD STEM FROM THE BEARDMORE GLACIER AREA

Silicified stems with typical cycadalean anatomy are described from specimens collected from the Fremouw Formation (Triassic) in the Transantarctic Mountains of Antarctica. Axes are slender with a large parenchymatous pith and cortex separated by a narrow ring of vascular tissue. Mucilage canals are present in both pith and cortex. Vascular tissue consists of endarch primary xylem, a narrow band of secondary xylem tracheids, cambial zone, and region of secondary phloem. Vascular bundles contain uni- to triseriate rays with larger rays up to 2 mm wide separating the individual bundles. Pitting on primary xylem elements ranges from helical to scalariform; secondary xylem tracheids exhibit alternate circular bordered pits. Traces, often accompanied by a mucilage canal, extend out through the large rays into the cortex where some assume a girdling configuration. A zone of periderm is present at the periphery of the stem. Large and small roots are attached to the stem and are conspicuous in the surrounding matrix. The anatomy of the Antarctic cycad is compared with that of other fossil and extant cycadalean stems.     

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.     

A WOODY LYCOPSID STEM FROM THE NEW ALBANY SHALE (LOWER MISSISSIPPIAN) OF KENTUCKY

A lycopsid axis from the New Albany Shale (Sanderson Formation) of Kentucky is described. The stem, which branches dichotomously, is 45 mm in diameter and is characterized by a relatively narrow parenchymatized protostele, a 3.0 mm-thick cylinder of secondary xylem, a tripartite cortex, and a periderm that is more than 5.0 mm thick. The secondary xylem is composed of uniseriate and biseriate vascular rays and narrow tracheids with scalariform wall thickenings on both radial and tangential walls. The periderm is characterized by elongate, thick-walled cells, some of which broaden tangentially in the outer part of the tissue forming zones that appear wedge-shaped in cross section. Surface features of the axis, including leaf bases, are not preserved. The stem is tentatively regarded as a member of the Lepidodendrales in accordance with the numerous anatomical characters that it shares with more recent representatives of the order. Because the external morphology is not known, however, the possibility exists that the axis corresponds to a protolepidodendralean taxon currently known only from compression and/or impression remains or some other nonlepidodendralean plant that produced secondary xylem. The extremely narrow profile of the secondary xylem tracheids (relative to other arborescent lycopsids) is interpreted as evidence that the plants grew in a habitat that was substantially drier than the Upper Carboniferous coal swamps.     

WOOD ANATOMY OF BUBBIA (WINTERACEAE), WITH COMMENTS ON ORIGIN OF VESSELS IN DICOTYLEDONS

Quantitative and qualitative features of wood anatomy are reported for ten collections of seven species of Bubbia. Variations on the basic plan for Winteraceae can be interpreted in terms of taxonomic and ecological distinctions. Tracheid length is correlated with plant size and habit: tracheids are shortest in shrubs. Tracheid wall thickness and ray cell wall thickness distinguish species. Ray cell procumbency and multiseriate ray width increase with age. Growth rings occur only in a species from stream margins. SEM studies reveal absence of a warty layer within tracheids. Helical thickenings are absent. Presence of these two features in Pseudowintera may be correlated with the cool temperate habitats of that genus. Overlap areas of tracheids in Bubbia show various degrees of scalariform pitting, ranging from none (B. semecarpoides) to abundant presence (B. balansae). Perforation-like pits in tracheids of the latter prove, with SEM studies, to have pit membranes containing porosities less than 1 μm in diameter. Scalariform pitting on overlap areas is absent in earlier secondary xylem and increases during later secondary xylem. Scalariform lateral wall pitting can occur in abnormally wide tracheids formed after pauses in cambial activity. These facts show that primitive dicotyledon woods like those of Bubbia can activate genetic information for scalariform end wall patterns and lateral wall pitting such as primitive vessels show without the intervention of paedomorphosis. Paedomorphosis in dicotyledon woods is held still to apply only to special herbaceous and herblike growth forms, not to primarily woody plants. Progenesis (in xylem, loss of secondary xylem) is not held to be necessary to account for the scalariform patterns seen in tracheary elements of primitive dicotyledons. Reasons are given for rejection of the hypothesis that Winteraceae and other woody dicotyledons (Amborella, Sarcandra, Tetracentron, Trochodendron) are secondarily vesselless.     

Spatial relation between xylem and phloem in the stem of Hibiscus cannabinus L. (Malvaceae)

The distribution of the phloem in relation to the xylem was examined in the stem of Hibiscus cannabinus L. with reference to a report in the literature that this species has internal (intraxylary) phloem, a feature not previously observed in the Malvaceae. In the present study, the stem was found to have phloem only outside the xylem (external or extraxylary phloem). In the protophloem, the sieve tubes are obliterated while the internode elongates and the associated cells become fibres with thick secondary walls. Fibres occur in the secondary phloem also. As seen in transections of stems, the secondary xylem forms a continuous ring. The primary xylem extends in the form of arcs into the pith. The tracheary cells of the protoxylem become crushed or completely obliterated in elongating internodes. The associated parenchyma cells either retain thin walls or develop secondary thickenings.     

New Observations on Leptophloeum rhombicum from the upper Devonian of Hubei,China

A petrified stem of Leptophloeum rhombicum is described from the Huangjiadeng Formation of the Upper Devonian in Changyang, Hubei. In the xylem of the axis, the secondary xylem is not preserved, the greatest part of the primary xylem is composed of metaxylem tracheids that are scalariform and have Williamson's striations. Based on their connections between adjacent transverse bars Witliamson's striations would be considered as a part of the secondary wall material. The small protoxylem tracheids form vertical ridges at the periphery of primary xylem cylinder. In cross section, the ridges appear as small radiating teeth of protoxylem. It provides further evidence that primary xylem in Leptophloeum rhombicum is similar to that in Carboniferous lepidodendrid lycopods. The opinion that the systematic position of Leptophloeum should be transferred from the Protolepidodendrales to the Lepidodendrales could be accepted and reaffirmed.     

Tracheid differentiation in tobacco pith cultures

Summary Sterile pith cultures of Nicotiana tabacum have been induced to form localized regions of differentiating tracheids. These localized regions have been examined by phase, fluorescence, and electron microscopy, and polarization optics. Fixation for electron microscopy was with glutaraldehyde-osmium. The differentiating tracheids develop characteristic thick cell walls which are eventually lignified. The lignifications appear to be uniform throughout the secondary wall and little or no lignin appears to be deposited in the primary walls or intercellular layer. At all stages of secondary wall deposition, the peripheral cytoplasm contains a system of microtubules which form a pattern similar to that of the developing thickenings. Within this system the microtubules are oriented, the direction of orientation mirroring that of the fibrils in the most recently deposited parts of the wall. The observations support the view that the microtubules are somehow involved in microfibril orientation. The microtubules appear to be attached to the plasma membrane which has a triple layered structure. The two electron dense layers of the plasma membrane have a particulate structure. In the differentiating tracheids at regions where secondary wall thickening has not yet been deposited numerous invaginations of the plasma membrane are observed which contain loosely organized fibrillar material. It is suggested that these are areas of localized activity of the plasma membrane and that the enzymes concerned with the final organization of the cellulose microfibrils are situated at the surface of the plasma membrane. Dictyosomes in the differentiation cells give rise to vesicles which contain fibrous material and the contents are incorporated into the cell wall. Numerous profiles characteristic of plasmodesmata are evident in sections of the secondary thickenings.Part of this work was carried out at the Osborne Memorial Laboratories, Yale University.     

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.     

湖北长阳上泥盆统一种石松植物

描述一种采自湖北上泥盆统弗拉阶黄家蹬组中的石松植物。该植物茎轴纤细。叶基纺锤形,螺旋排列。叶线形,叶缘具刺。具顶生的孢子叶球。其孢子叶匙状或披针形,边缘具刺。孢子囊呈圆形或椭圆形。植物茎具原生中柱。原生木质部呈小脊状位于中柱边缘。后生木质部管胞由梯纹分子组成,在加厚棒之间没有类似“威廉姆逊纹”的连接物。该植物与采自湖南中泥盆统基维特阶的Longostachys(Zhu,Huand Feng) Caiand Chen可比较。它们在茎轴、线形和具刺的叶、纺锤形和螺旋排列的叶基、匙状披针形的孢子叶,以及叶、叶基和孢子叶的度量等特征方面均非常相似。两者在解剖特征上存有差别,即当前植物不具次生木质部,不具髓,后生木质部加厚棒之间不具连接物。考虑到现有特征并不足以建立新属种,暂归入cf.Longostachyssp.     

The origin and early evolution of tracheids in vascular plants: integration of palaeobotanical and neobotanical data

Although there is clear evidence for the establishment of terrestrial plant life by the end of the Ordovician, the fossil record indicates that land plants remained extremely small and structurally simple until the Late Silurian. Among the events associated with this first major radiation of land plants is the evolution of tracheids, complex water-conducting cells defined by the presence of lignified secondary cell wall thickenings. Recent palaeobotanical analyses indicate that Early Devonian tracheids appear to possess secondary cell wall thickenings composed of two distinct layers: a degradation-prone layer adjacent to the primary cell wall and a degradation-resistant (possibly lignified) layer next to the cell lumen. In order to understand better the early evolution of tracheids, developmental and comparative studies of key basal (and potentially plesiomorphic) extant vascular plants have been initiated. Ultrastructural analysis and enzyme degradation studies of wall structure (to approximate diagenetic alterations of fossil tracheid structure) have been conducted on basal members of each of the two major clades of extant vascular plants: Huperzia (Lycophytina) and Equisetum (Euphyllophytina. This research demonstrates that secondary cell walls of extant basal vascular plants include a degradation-prone layer ('template layer') and a degradation-resistant layer ('resistant layer'). This pattern of secondary cell wall formation in the water-conducting cells of extant vascular plants matches the pattern of wall thickenings in the tracheids of early fossil vascular plants and provides a key evolutionary link between tracheids of living vascular plants and those of their earliest fossil ancestors. Further studies of tracheid development and structure among basal extant vascular plants will lead to a more precise reconstruction of the early evolution of water-conducting tissues in land plants, and will add to the current limited knowledge of spatial, temporal and cytochemical aspects of cell wall formation in tracheary elements of vascular plants.     

Fossil wood of Eristophyton sp. from the Carboniferous deposits of northern Russia (Arkhangelsk region)

Permineralised wood of Eristophyton sp. is first described from the Carboniferous deposits of the Arkhangelsk region, northern Russia. The specimens used in the study show scalariform thickening of the metaxylem tracheids both on radial and tangential walls. Eristophyton sp. indicates well preserved elements of secondary xylem: uni-, rarely biseriate xylem rays up to 15–16 cells high; uni-, multiseriate tracheid pitting only on radial walls; 1–8 contiguous cross-field pits and their inclined narrow apertures. A brief review and comparison with known anatomically preserved plants from the Lower Carboniferous of different localities of Scotland, France, USA and Poland is discussed.     

慈姑不定根中导管分子的观察

慈姑导管仅在根中出现。根的后生木质部中央导管由顶端平截、单穿孔的网纹导管分子连接组成;周围较小的导管分子和管胞有从梯纹管胞向导管分子演化的各种过渡类型;有一至多个梯形穿孔或单穿孔发生在导管分子的端壁或侧壁,并有分枝型导管分子存在,特别在根与主茎连接处尤为明显。管胞亦有分枝与不分枝的类型。     

Structural and systematic study of an unusual tracheid type in cacti

Wide-band tracheids are a specialized tracheid type in which an annular or helical secondary wall projects deeply into the cell lumen. They are short, wide and spindle-shaped, and their bandlike secondary walls cover little of the primary wall, leaving most of it available for water diffusion. Wide-band tracheids appear to store and conduct water while preventing the spread of embolisms. They may be the most abundant tracheary element in the xylem, but they are always accompanied by at least a few vessels. Typically, fibers are absent wherever wide-band tracheids are present. Wide-band tracheids occur in the primary and secondary xylem of succulent stems, leaves and roots in genera of all three subfamilies of Cactaceae but were not found in the relictual genusPereskia, which lacks succulent tissues. In the large subfamily Cactoideae, wide-band tracheids occur only in derived members, and wide-band tracheids of North American Cactoideae are narrower and are aligned in a more orderly radial pattern than those of South American Cactoideae. Wide-band tracheids probably arose at least three times in Cactaceae.     

Water transport in xylem conduits with ring thickenings

Helical or annular wall thickenings are not only present in protoxylem, but may also he a feature of the tracheids or vessel elements of secondary wood. The frequency of their occurrence tends to be a function of climatic factors and conduit diameter. In order to obtain a functional explanation for these structures, the hydrodynamic behaviour of xylem conduits with various patterns of annular wall thickenings was investigated numerically using a commercial CFD (Computational Fluid Dynamics) package. The fluid flow phenomena are presented in detail. The calculations show that the developing pressure gradient of the structures with corrugated walls is in each case lower than that of a smooth pipe with a diameter corresponding to the distance between two opposite thickenings. Furthermore, complex flow patterns with circulation zones between the thickenings develop which are dependent on the geometry of the wall. It may be hypothesized that these circulation zones influence the lateral water flow. The results are discussed with regard to the relationships between the water conduction function of the xylem and ecological factors.     

The role of microtubules in vessel member differentiation inColeus

Summary The role of microtubules in tracheary element formation in cultured stem segments ofColeus has been investigated through the use of the antimicrotubule drug, colchicine. Colchicine treatment of the cultured stem segments produced a dual effect on xylem differentiation. If applied at the time of stem segment isolation or shortly thereafter, wound vessel member formation is almost completely blocked. However, if colchicine is applied after the third day of culture, it does not inhibit differentiation, but instead large numbers of xylem elements are formed which have highly deformed secondary walls. Both effects are related to colchicine's specific affinity for microtubules. In the first case it is shown that colchicine blocks mitosis, presumably by destroying the spindle apparatus, and thus inhibits divisions which are prerequisite for the initiation of xylem differentiation. While, if colchicine is applied after the necessary preparative divisions have taken place, it destroys specifically the cortical microtubules associated with the developing bands of secondary wall, thus causing aberrant wall deposition.Light and electron microscopic analysis of drug-treated cells reveals that the secondary wall becomes smeared over the surface of the primary wall and does not retain the discrete banded pattern characteristic of secondary thickenings in untreated cells. Examination of colchicine-treated secondary walls in KMnO₄ fixed material shows that in the absence of microtubules the cellulose microfibrils lose their normal parallel orientation and are deposited in swirls and curved configurations, and often lie at sharp angles to the axis of the secondary wall band. Microtubules, thus, appear to play a major role in defining the pattern of secondary wall deposition and in directing the orientation of the cellulose microfibrils of the wall. Factors in addition to microtubules also act in controlling the secondary wall pattern, since we observe that even in the absence of microtubules secondary thickenings of two adjacent xylem elements are deposited directly opposite one another across the common primary wall.     

STEM ANATOMY OF PARTHENIUM ARGENTATUM,P. INCANUM AND THEIR NATURAL HYBRIDS

Guayule (Parthenium argentatum Gray) contains rubber in the parenchymatous cells of stems and roots. Stem anatomy of P. argentatum is described along with that of P. incanum H.B.K. (mariola). Anatomy of these species differs significantly. Phloem rays in both species increase in width by cell division and expansion; however, the increase observed in mariola is less as compared to that in guayule. Axial xylem parenchyma in guayule is generally a two-cell strand as compared to the fusiform axial xylem parenchyma observed in mariola. Vascular ray cells and cells of the pith region of guayule are parenchymatous, whereas those of mariola are sclerenchymatous. As a result of introgression between guayule and mariola, three forms of guayule exist in the native stands of Mexico. Morphological differences between these guayule plants have been described previously. The stem anatomy of these three groups of plants differ importantly. Group I guayule plants, least introgressed by mariola, have taller rays with the cells of pith region and vascular rays parenchymatous. Group III plants, highly introgressed by mariola, have a few to many cells of vascular rays and pith with lignified secondary walls and shorter rays. Many of the anatomical characteristics of group II plants, somewhat introgressed by mariola, are intermediate between group I and III plants.     

Xylem of early angiosperms: Novel microstructure in stem tracheids of Barclaya (Nymphaeaceae)

Pit membranes of stem tracheids of all recognized species of Barclaya, an Indomalaysian genus of Nymphaeaceae, were studied with scanning electron microscopy (SEM). Pit membranes of the tracheids are composed of two thick layers, both constructed of fibrils much larger than those of tracheary elements of angiosperms other than Nymphaeaceae. The outer (distal) layer, which comprises the continuous primary wall around the tracheids, is spongiform, perforated by porosities of relatively uniform size, and confined to or most prominent on end walls of stem tracheids. The second layer consists of thick widely spaced fibrils that are oriented axially and are laid down proximally (facing the cell lumen) to the first (outer) layer, although continuous with it. These axial fibrils are attached at their ends to the pit cavities. This peculiar microstructure is not known outside Nymphaeaceae except in Brasenia and Cabomba (Cabombaceae, Nymphaeales), and has not been previously described for Barclaya. The longitudinally oriented threads and strands in perforation plates of secondary xylem of wood and stems of a variety of primitive woody angiosperms (e.g., Illicium) are not homologous to the pit membrane structure observed in stem tracheids of Barclaya, which, like other Nymphaeaceae, has only primary xylem and no perforation plates. The tracheid microstructure reported here is different from pit structures observed in any other group of vascular plants, living or fossil. The tracheid stem microstructures of Barclaya and other Nymphaeaceae appear to be a synapomorphy of Nymphaeaceae and Cabombaceae, and need further study with respect to ultrastructure and function.