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1.
SEM studies on vessels in ferns. 11. Ophioglossum   总被引:4,自引:0,他引:4  
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.  相似文献
2.
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.  相似文献
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For the single species of Austmbaileya (Austrobaileyaceae), quantitative and qualitative data are offered on the basis of a mature stem and a root of moderate diameter. Data available hitherto have been based on stems of small to moderate diameter, and roots have not previously been studied. Scanning electron microscope (SEM) photographs are utilized for roots, and show compound starch grains. Roots lack sclerenchyma but have relatively narrow vessels and abundant ray tissue. Recent phylogenies group Austrobaileyaceae with the woody families Illiciaceae, Schisandraceae, and Trimeniaceae (these four may be considered Illiciales), and somewhat less closely with the vesselless families Amborellaceae and Winteraceae and the aquatic families Cambombaceae and Nymphaeaceae. The vessel-bearing woody families above share vessels with scalariform perforation plates; bordered bars on plates; pit membrane remnants present in perforations; lateral wall pitting of vessels mostly alternate and opposite; tracheids and/or septate fibre-tracheids present; axial parenchyma vasicentric (sometimes abaxial); rays Heterogeneous Type I; ethereal oil cells present; stomata paracytic or variants of paracytic. Although comparisons between vessel-bearing and vesselless families must depend on fewer features, Amborellaceae and Winteraceae have no features incompatible with their inclusion in an expanded Illiciales.  相似文献
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Wood, bark and stem anatomy of New World species of Gnetum   总被引:1,自引:0,他引:1  
Quantitative and qualitative data are presented for 11 collections of six species. The wide range of character states for the species is presented in the form of a key to emphasize their potential systematic correlations. Distinctive among these are phcllem characteristics. Fibre-tracheids are newly reported for lianoid Gnetum species. Cells previously thought to be like companion cells in secondary phloem are shown to be uniseriate rays, counterparts to uniseriate xylem rays. Laticifers are abundant in most of the species, and are newly described for secondary tissues of Gnetum. Presence of tyloses in laticifers of two species is apparently a new report for vascular plants. Tori are present in two New World Gnetum species, adding to the report in African species. Perforation plates are simple except near or in primary xylem, where they are simple or foraminate. Torus presence and foraminate perforation plate presence are features more reminiscent of Ephedra and other gymnosperms than of angiosperms. The bark of Gnetum is also very similar to that of Ephedra.  相似文献
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Successive cambia in Aizoaceae: products and process   总被引:1,自引:0,他引:1  
The transverse and longitudinal sections of the stems and roots of 11 genera of Aizoaceae, representing a wide range of growth forms from hard fibrous stems to fibre‐free roots, were studied using light microscopy and scanning electron microscopy. In most of the genera, fibres are the first xylary product of each vascular cambium, followed by vessels in a parenchyma background. Variations on this pattern help to prove that fibres are produced by vascular cambia, except in Ruschia and Stayneria, in which both the lateral meristem and the vascular cambia produce fibres. Cylinders of conjunctive tissue parenchyma that alternate with the vascular cylinders are produced by the lateral meristem. The concept that the lateral meristem gives rise to the vascular cambia and secondary cortex is supported by photographic evidence. Radial divisions occur in the origin of the lateral meristem, and then again as vascular cambia arise from the lateral meristem; these radial divisions account for storeying in fibres and conjunctive tissue. Raylessness characterizes all Aizoaceae studied, with the exception of Tetragonia, which also differs from the remaining genera by having vasicentric axial parenchyma, a scattering of vessels amongst fibres, and the presence of druses instead of raphides. Several vascular cambia are typically formed per year. Several vascular cambia are active simultaneously in a given stem or root. Roots have fewer fibres and more abundant conjunctive tissue parenchyma than stems. Successive cambia result in an ideal dispersion of vascular tissue with respect to water and photosynthate storage and retrieval capabilities of the parenchyma, and to liana stem plans. The distribution and relative abundance of fibres, vessels, secondary phloem, and conjunctive tissue parenchyma relate primarily to habit and are not a good source of systematic data, with the probable exception of Tetragonia. The general pattern of lateral meristem and vascular cambial ontogeny is the same as in other families of the core Caryophyllales, although the patterns of the tissues produced are diverse. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society, 2007, 153 , 141–155.  相似文献
9.
Bordered pits occur in walls of living ray cells of numerous species of woody dicotyledons. The occurrence of this feature has been minimally reported because the pits are relatively small and not easily observed in face view. Bordered pits are illustrated in sectional view with light microscopy and with scanning electron microscopy in face view for dicotyledonous and gnetalean woods. Bordered pits are more numerous and often have prominent borders on tangential walls of procumbent ray cells, but also occur on radial walls; they are approximately equally abundant on tangential and horizontal walls of upright cells, suggesting parallels to cell shape in flow pathway design. Axial parenchyma typically has secondary walls thinner than those of ray cells, but bordered pits or large simple pit areas occur on some cross walls of parenchyma strands. There is no apparent correlation between the phylogenetic position of species and the presence of borders in ray cells or axial parenchyma. Bordered pits represent a compromise between maximal mechanical strength and maximal conductive capability. High rates of flow of sugar solutions may occur if starch in ray cells or axial parenchyma is mobilized for sudden osmotic enhancement of the conductive stream or for rapid development of foliage, flowers, or fruits. Measurement of the secondary wall thickness of ray cells may offer simple inferential information about the role that rays play in the mechanical strength of woods. © 2007 The Linnean Society of London, Botanical Journal of the Linnean Society , 2007, 153 , 157–168.  相似文献
10.
CARLQUIST, S., 1984. Wood and stem anatomy of Lardizabalaceae, with comments on the vining habit, ecology and systematics. Qualitative and quantitative data, based mostly upon liquid-preserved specimens, are presented for Akebia, Roquila, Decaisnea, Holbodia, Lardizabala, Sinofranchetia and Stauntonia . Because Decaisnea is a shrub whereas the other genera are vines, anatomical differences attributable to the scandent habit can be considered. These include exceptionally wide vessels, a high proportion of vessels to tracheids (or other imperforate trdcheary elements) as seen in transection, simple perforation plates, multiseriate rays which are wide and tall, and pith which is partly or wholly sclerenchymatous. With respect to ecology, two features are discussed: spirals in narrower vessels may relate to adaptation to freezing in the species of colder areas, and crystalliferous sclereids seem adapted in morphology and position to deterrence of phytophagous insects or herbivores. The wood may provide mechanisms for maintaining conduction even if wider vessels are deactivated temporarily by formation of air embolisms. Wood and stem anatomy of Lardizabalaceae compare closely to those of Berberidaceae and of Clematis (Ranunculaceae), as well as to other families of Berberidales. Decaisnea is more primitive than these in having consistently sralariform perforation plates and in having scalariform pitting on lateral walls of vessels. A tentative listing of anatomical features which may correspond to generic limits is given.  相似文献
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