SEM studies on vessels in ferns. 11. Ophioglossum

With scanning electron microscopy (SEM), the nature of metaxylem vessel elements and tracheids was examined in Ophioglossum crotalophomides, 0. pendulum subsp. falcatum , and 0. vulgatum roots and rhizomes. Vessels were identified in all species. End walls of vessel elements, which bear perforations, are like lateral wall pitting of those elements in the secondary wall framework and differ only in absence of pit membranes or presence of pit membrane remnants. Some of the perforations contain pit membrane remnants that have large pores, small porosities, or are threadlike or weblike in structure. Dimorphic perforations were found in some vessel elements of rhizomes of 0. pendulum subsp. falcatum. Tracheids are very likely present in addition to vessels in all three species. The secondary wall framework of both tracheids and vessels is basically scalariform, although deviations in pattern are present. Vessel elements of Ophiglossum are entirely comparable to those of leptosporangiate ferns.     

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.     

SEM studies on vessels in ferns. 9. Dicranopteris (Gleicheniaceae) and vessel patterns in leptosporangiate ferns

Ferns in which vessels have been demonstrated to date are phylogenetically relatively specialized and characteristic of habitats with marked extremes in temperature and water availability. These specifications do not apply to the Gleicheniaceae, which indicates that vessels may occur in a range of more primitive ferns, including those from more nearly mesic habitats. Vessels in Dicranopteris have perforation plates (both lateral and terminal) with morphology similar to that of lateral wall pitting as seen with light microscopy. Scanning electron microscopy (SEM) is therefore necessary to demonstrate presence of perforations. Vessel presence in Dicranopteris is important in forming a picture of vessel presence and specialization in ferns, the phylogenetic and ecological distribution of which may differ from the patterns found in monocotyledons and dicotyledons. We believe that presence of vessels may not be a reliable indicator of phylogenetic position among ferns.     

Vessels in ferns: structural, ecological, and evolutionary significance

We have studied macerated xylem of ferns, supplemented by sections, by means of scanning electron microscopy (SEM) in a series of 20 papers, the results of which are summarized and interpreted here. Studies were based mostly on macerations, but also on some sections; these methods should be supplemented by other methods to confirm or modify the findings presented. Guidelines are cited for our interpretations of features of pit membranes. Fern xylem offers many distinctive features: (1) presence of numerous vessels and various numbers of tracheids in most species; (2) presence of vessels in both roots and rhizomes in virtually all species; (3) presence of specialized end walls in vessels of only a few species; (4) multiple end-wall perforation plates in numerous species; (5) lateral-wall perforation plates in numerous species; (6) porose pit membranes associated with perforation plates in all species; and (7) pit dimorphism, yielding wide membrane-free perforations alternating with extremely narrow pits. Multiple end wall perforation plates and lateral wall perforation plates are associated with the packing of tracheary elements in fascicles in ferns: facets of tips of elements contact numerous facets of adjacent elements; all such contacts are potential sites for conduction by means of perforations. This packing differs from that in primary xylem of dicotyledons and monocotyledons. Porosities in pit membranes represent a way of interconnecting vessel elements within a rhizome or root. In addition, these porosities can interconnect rhizome vessel elements with those of roots, a feature of importance because roots are adventitious in ferns as opposed to those of vascular plants with taproots. Fully-formed or incipient (small-to-medium sized porosities in pit membranes) perforation plates are widespread in ferns. These are believed to represent (1) ease of lysis of pit membranes via pectinase and cellulase; (2) numerous potential sites for perforation plate formation because of fasciculate packing of tracheary elements; (3) evolution of ferns over a long period of time, so that lysis pathways have had time to form; (4) lack of disadvantage in perforation plate presence, regardless of whether habitat moisture fluctuates markedly or little, because ferns likely have maintaining integrity of water columns that override the embolism-confining advantage of tracheids. Although all ferns share some common features, the diversity in xylem anatomy discovered thus far in ferns suggests that much remains to be learned.     

SEM studies on vessels in ferns. 17. Psilotaceae

Perforation plates are reported in aerial and subaerial axes of Psilotum nudum and in aerial axes of Tmesipteris obliqua. In Psilotum, both perforations lacking pit membranes and perforations with pit membrane remnants were observed. Perforation plates in Psilotum may consist wholly of one type or the other. In Tmespteris, perforations have threadlike pit membranes or consist of porose pit membranes. Wide perforations alternating with narrow pits, a conformation observed in various ferns, were observed in Psilotum (subaerial axes). In Psilotum, perforations are more common in metaxylem than in protoxylem; perforations in protoxylem consist of primary wall areas containing small circular porosities or relatively large circular to oval perforations. There are no modifications in the secondary wall framework of protoxylem or metaxylem in Psilotum or Tmesipteris that would permit one to distinguish presence of perforations or perforation plates with light microscopy, and scanning electron microscopy (SEM) is required for demonstration of porose walls or perforations. The tracheary elements of the Psilotaceae studied have no features not also observed in other ferns with SEM.     

国产对囊蕨亚科(蹄盖蕨科)植物的管状分子

利用扫描电镜观察了国产蹄盖蕨科(Athyriaceae)对囊蕨亚科(Deparioideae)10种植物及双盖蕨属(Diplazium Sw.)3种植物根状茎的管状分子。结果显示, 这些管状分子端壁和侧壁的形态及结构分别相同且侧壁具有穿孔板(多穿孔板)。根据穿孔板的形态特征, 将该亚科的管状分子分为5种类型: (1)梯状穿孔板, 无穿孔的二型性现象; (2)梯状穿孔板, 有穿孔的二型性现象; (3)网状穿孔板; (4)梯状-网状混合的穿孔板; (5)大孔状穿孔板。按照纹孔膜残留的程度又可分为3种: 部分区域有完整的纹孔膜、残留呈网状或线状以及很少或无纹孔膜残留。结合前人的研究资料, 发现蕨类植物的管状分子与被子植物的导管分子在形态和输导机理上存在明显差异, 管胞和导管分子不能仅仅根据纹孔膜的存在与否来确定, 而应根据穿孔板存在于端壁还是侧壁进行判断, 即穿孔板仅存在于端壁的管状分子为导管分子; 端壁和侧壁形态及结构分别相同, 有或无穿孔板的管状分子为管胞。由此可以推测蕨类植物和裸子植物中输导水分和矿物质的管状分子主要为管胞。单叶双盖蕨属(Triblemma(J. Sm.) Ching)与双盖蕨属管状分子的特征并不相似, 显示了将单叶双盖蕨属从双盖蕨属独立出来归入对囊蕨亚科的合理性。根据管状分子的特征, 推测假蹄盖蕨属(Athyriopsis Ching)和蛾眉蕨属(Lunathyrium Koidz.)可能是比较进化的属, 而介蕨属 (Dryoathyrium Ching)相对比较原始, 单叶双盖蕨属的系统位置应介于假蹄盖蕨属与介蕨属之间。     

国产对囊蕨亚科（蹄盖蕨科）植物的管状分子

利用扫描电镜观察了国产蹄盖蕨科（Athyriaceae）对囊蕨亚科（Deparioideae）10种植物及双盖蕨属（Diplazium Sw．）3种植物根状茎的管状分子。结果显示,这些管状分子端壁和侧壁的形态及结构分别相同且侧壁具有穿孔板（多穿孔板）。根据穿孔板的形态特征,将该亚科的管状分子分为5种类型：（1）梯状穿孔板,无穿孔的二型性现象：（2）梯状穿孔板,有穿孔的二型性现象：（3）网状穿孔板：（4）梯状-网状混合的穿孔板：（5）大孔状穿孔板。按照纹孔膜残留的程度又可分为3种：部分区域有完整的纹孔膜、残留呈网状或线状以及很少或无纹孔膜残留。结合前人的研究资料,发现蕨类植物的管状分子与被子植物的导管分子在形态和输导机理上存在明显差异,管胞和导管分子不能仅仅根据纹孔膜的存在与否来确定,而应根据穿孔板存在于端壁还是侧壁进行判断,即穿孔板仅存在于端壁的管状分子为导管分子：端壁和侧壁形态及结构分别相同,有或无穿孔板的管状分子为管胞。由此可以推测蕨类植物和裸子植物中输导水分和矿物质的管状分子主要为管胞。单叶双盖蕨属（Triblemma（J．Sm．）Ching）与双盖蕨属管状分子的特征并不相似,显示了将单叶双盖蕨属从双盖蕨属独立出来归人对囊蕨亚科的合理性。根据管状分子的特征,推测假蹄盖蕨属（Athyriopsis Ching）和蛾眉蕨属（Lunathyrium Koidz．）可能是比较进化的属,而介蕨属（Dryoathyrium Ching）相对比较原始,单叶双盖蕨属的系统位置应介于假蹄盖蕨属与介蕨属之间。     

国产球盖蕨科植物管状分子的比较研究

利用扫描电镜观察了国产球盖蕨科10种植物,鳞毛蕨科6种植物的管状分子,结果显示:它们的管状分子端壁和侧壁的形态及结构分别相同,且侧壁具有穿孔板。它们具有4种类型的管状分子:(1)梯状穿孔板,无穿孔板的二型性现象;(2)梯状穿孔板,具有二型性现象;(3)梯状-网状混合穿孔板;(4)大孔状穿孔板。穿孔板仅存在于端壁的管状分子为导管分子,而端壁和侧壁形态、结构相似,有或无穿孔板的管状分子为管胞,蕨类植物中的管状分子主要为管胞,这与传统观点不同。管状分子的形态特征表明:球盖蕨科是鳞毛蕨群的成员,但不是原始成员,可能属于其中较为进化的类群,与鳞毛蕨科有许多共同特征,但仍存在较大差异,所以将其作为独立的科是合理的,推测球盖蕨科中的鱼鳞蕨属是比较进化的属,柄盖蕨属相对原始,红腺蕨属的系统位置应介于二者之间。     

Pit membrane remnants in perforation plates and other vessel details of Cornales

Perforation plates and other vessel details as studied with scanning electron microscopy (SEM) have been reported for four species of Cornaceae (s.l.): similar features are shown by the four, suggesting that a more extensive sampling of the family might reveal similar phenomena. Perforation plates contain pit membrane remnants in the form of threads or, less commonly, laminar portions perforated by pores. When least well-represented, the pit membrane remnants are restricted to lateral ends of perforations and to the perforations transitional to lateral wall pitting. Perforations are all clearly bordered. Helical thickenings that do not form a continuous gyre are reported for the vessel walls ofAucuba. The presence of pit membrane remnants in vessel elements of Cornaceae correlates with the mesic habitats occupied by species in this family. The presence and type of pit membrane remnants reported by us in the three genera is very similar, although pit membrane remnants are doubtless a symplesiomorphy and thus not an indicator of relationships. The presence of pit membrane remnants in the three genera, however, does attest to the primitiveness of wood and other features of Cornaceae s.l.     

Pit membrane remnants in perforation plates of Hydrangeales with comments on pit membrane remnant occurrence, physiological significance and phylogenetic distribution in dicotyledons

Perforation plates from ten species of seven genera of Hydrangeales sensu Thorne were studied using scanning electron microscopy (SEM). The presence of pit membranes in perforations ranges from abundant, as in Carpenteria and Hydrangea, to minimal, as in Deutzia, Escallonia and Philadelphus. Abnormally great pit membrane presence may result from the presence of secondary compounds that inhibit lysis, as in Quintinia serrata; such interference with the natural lysis process may or may not be evident from coarseness and irregularity of pit membrane surface and of threads composing the pit membrane remnants. The presence of pit membrane remnants in perforation plates is hypothesized to be a symplesiomorphy, found in a fraction of dicotyledons with scalariform perforation plates (but still in an appreciable number of species). Pit membrane remnant presence may represent incomplete lysis of primary wall material (cellulose microfibrils) in species that occupy highly mesic habitats, where such impedance in the conductive stream does not have an appreciable negative selective value. This physiological interpretation of pit membrane remnants in perforations is enhanced by the phylogenetic distribution as well as the strongly mesic ecological preferences of species that exemplify this phenomenon in dicotyledons at large. Families with pit membrane presence in perforations are scattered throughout phylogenetic trees, but they occur most often in basal branches of major clades (superorders) or as basal branches of orders within the major clades. Further study will doubtless reveal other families and genera in which this phenomenon occurs, although it is readily detected only with SEM. Phylogenetic stages in the disappearance of pit membrane remnants from perforation plates are described, ranging from intact pit membranes except for presence of pores of various sizes, to presence of membrane remnants only at lateral ends of perforations and in one or two perforations (arguably pits) at the transition between a perforation plate and subadjacent lateral wall pitting. Developmental study of the mechanism and timing of lysis of pit membranes in perforations, and assessment of the role of the conductive stream in their removal, are needed to enhance present understanding of vessel evolution. © 2004 The Linnean Society of London, Botanical Journal of the Linnean Society, 2004, 146 , 41–51.     

Origin and nature of vessels in monocotyledons. 5. Araceae subfamily Colocasioideae

Tracheary elements from macerations of roots and stems of one species each of five genera of Araceae subfamily Colocasioideae were studied by means of SEM (scanning electron microscopy). All of the genera have vessel elements not merely in roots, as previously reported for the family as a whole, but also in stems. The vessel elements of stems in all genera other than Syngonium are less specialized than those of roots; stem vessel elements are tracheid-like and have porose pit membrane remnants in perforations. The perforations with pit membrane remnants demonstrate probable early stages in evolution of vessels from tracheids in primary xylem of monocotyledons. The vessel elements with such incipient perforation plates lack differentiation in secondary wall thickenings between perforation plate and lateral wall, and such vessel elements cannot be identified with any reliability by means of light microscopy. The discrepancy in specialization between root and stem vessel elements in genera other than Syngonium is ascribed to probable high conductive rates in roots where soil moisture fluctuates markedly, in contrast with the storage nature of stems, in which selective value for rapid conduction is less. Syngonium stem vessels are considered adapted for rapid conduction because the stems in that genus are scandent. Correlation between vessel element morphology and ecology and habit are supported. Although large porosities in vessel elements facilitate conduction, smaller porosities may merely represent rudimentary pit membrane lysis.     

Vestigial pit membrane remnants in perforation plates and helical thickenings in vessels of Ericaceae

Perforation plates from 15 species of 10 genera with scalarifom perforation plates, representing three subfamilies of woody Ericaceae (Rhododendroideae, Arbutoideae, Vaccinioideae) were studied with scanning electron microscopy (SEM). In most of them, pit membrane remnants were present, but these remnants were less extensive than in the ericalean families Clethraceae, Cyrillaceae, and Sarraceniaceae. Pit membrane remnants in perforations of vessels of Ericaceae are characteristically found at lateral ends of the perforations and in perforations (which may alternatively be called pits) transitional to lateral wall pitting. Pit membrane remnants were most extensive in Enkianthus. Phylogenetic and physiological factors for vestigial membrane presence in the perforations are discussed. Helical thickenings on vessel walls as seen with SEM are figured and described for Leucothoe and Pieris, and their significance is assessed.     

10 种茶藨子属植物导管分子形态特征及其生态适应性比较研究简

利用光学显微镜和扫描电子显微电镜,以10种茶藨子属植物为研究材料,观察了其导管分子的形态结构。结果显示：（1）所研究的茶藨子属植物导管分子穿孔板为梯状穿孔板,且穿孔板上横隔分布的数量不同,端壁倾斜角度种间变化不大;（2）导管分子纹孔式样为互列式或兼有互列式和对列式,纹孔形状种间存在差异;（3）有的种类导管分子内壁有螺纹加厚或网状凸起。研究表明,不同生境下的茶藨子属植物导管形态与其生态适应性之间有较强的相关性,表现为湿生环境的物种导管较短,直径较宽;旱生环境的物种导管较长,直径较小;中生环境的居中。本文分析了茶藨子属植物导管分子形态特征的生态适应性。     

Vessel elements present in the secondary xylem of Trochodendron and Tetracentron (Trochodendraceae)

For almost 150 years, the two monotypic genera Trochodendron and Tetracentron (Trochodendraceae) have been considered to share an unusual and primitive feature in angiosperms - the lack of vessels in their wood. Therefore, they have been classified in a basal position in the angiosperms. Our observations by light microscopy, low-vacuum environmental scanning electron microscopy (ESEM) and high-vacuum scanning electron microscopy (SEM) both in fresh and FAA-fixed materials consistently showed the presence of tracheary elements differentiated into two types in both genera. In Trochodendron, the tracheary elements can be divided into perforate vessel elements and imperforate fiber-tracheids and tracheids. The vessel elements show end and lateral walls. The pits on the end walls are elongate- broadened and do not have membranes or only a few remnants of them forming the perforation plates. The fiber-tracheids show crossfield pit pairs and sharp ends, and the tracheids show bordered pits. In Tetracentron, the tracheary elements comprise vessel elements and fibers. The vessel elements are similar to those of Trochodendron, whereas the fibers have no crossfield pit pairs but, rather, elliptical pits and sharp ends. Thus, both Trochodendron and Tetracentron are vessel bearing rather than vesselless, although their vessel elements are primitive.     

Study on the Convergent Passages of Water Conducting Elements in Secondary Xylem of Fagaceae

Structural variations in the convergent passages of water conducting elements were described in secondary xylem of 70 species of Fagaceae. Two types of water conducting systems were recognized on the ground of water-flow directions. The convergent passages of the longitudinal system mainly exhibited in the forms as perforations between the ends of Vessel elements, lateral wall pitting between the lateral walls of vessel elements, pitting be-tween vessel elements and imperforate tracheary elements, and pitting between imperforate tracheary elements. The convergent passages in the transverse system consisted of pitting between vessel elements and ray cells, pitting between imperforated tracheary elements and ray cells and simple pitting between ray cells. In addition, the roles of vasicentric tracheids and broad rays played in terms of conducting effectiveness and efficiency as proposed by Zimmermann were discussed.     

蜈蚣草导管分子的观察

对蜈蚣草(Pteris vittata)叶轴中导管分子进行了观察。结果表明,其导管分子十分细长,均具长、且十分倾斜的梯状穿孔板,穿孔没有纹孔膜的残余,与侧壁上的梯纹纹孔有着明显的差异。     

蜈蚣草导管分子的观察

对蜈蚣草(Pteris vittata)叶轴中导管分子进行了观察。结果表明,其导管分子十分细长,均具长、且十分倾斜的梯状穿孔板,穿孔没有纹孔膜的残余,与侧壁上的梯纹纹孔有着明显的差异。     

壳斗科次生木质部水分输导分子间连接通道结构的研究

壳斗科次生木质部水分运输聚合体及其连接通道结构,根据水分运输方向可分纵向和横向两大系统。水分纵向运输通道有导管分子间的穿孔,导管分子侧壁间的管间纹孔,导管分子与无穿孔管状分子间的侧壁纹孔,无穿孔管状分子与无穿孔管状分子间的侧壁纹孔。     

Vessel origins in Nymphaeaceae: Euryale and Victoria

Metaxylem tracheary elements of roots have differentiation between end walls and lateral walls in both Euryale and Victoria End walls have narrower, more closely spaced bars and scalariform plates. primary walls of end walls (and, to a lesser extent, lateral walls) have striations that are thickened primary wall portions orientated in an axial direction. These striations are less common in Victoria than in Euryale. Although secondary wall strands between perforations occur in some dicotyledons, the report of primary wall striations is new; these can be seen with scanning electron microscopy (SEM) but not with light microscopy. Perforations occur irregularly and sometimes sparsely on end walls of tracheary elements of Victoria , but perforations were not observed in Euryale. Thus, Euryale satisfies one criterion for the presence of vessel (end wall different from lateral wall), whereas Barclaya satisfies another (perforations in end walls) and Victoria satisfies both. Vessel origins in Nymphaeaceae are important in illustrating that there may be multiple vessel origins in dicotyledons.     

The anatomy of lotus fibers found in petioles of Nelumbo nucifera

Lotus fibers are the isolated helical secondary cell wall thickenings from tracheary elements of lotus (Nelumbo nucifera Gaertn) petioles. In this study the anatomical characteristics of lotus petioles and microstructures of tracheary elements were studied using light microscopy (LM) and scanning electron microscopy (SEM). The results show that vascular bundles of lotus petioles are scattered throughout ground tissue. Their tracheary elements are of various sizes and there are several patterns of secondary wall thickening present. However, only secondary thickening in a ribbon-like helical pattern can be drawn out from the petiole to form lotus fibers for subsequent utilization. Study of the microstructure of the tracheary elements reveals that there are two pit structures present in the end walls in addition to pits with intact pit membranes: those with porose or web-like remnants pit membrane and those that lack pit membranes. This is an indication of the transitional stage between tracheids and vessel elements. This study provides supportive evidence that lotus fibers are found in both helically thickened tracheids and helically thickened primitive vessels.