Wood and bark anatomy of the African species of Gnetum

Quantitative and qualitative data are given for the two African species of Gnetum ( Gnetum section Gnetum subsection Micrognemones ). These species are lianoid and lack the fibre-tracheids of G. gnemon but have about the same vessel element and tracheid length as in that species. Vessel diameter is related to stem age and organography. Tori are clearly present in tracheary elements of the African Gnetum species, a first report for the genus. In these two species, origin of the lateral meristem, which produces vascular tissue and cambia, can be traced directly and indirecdy to cortical parenchyma. A second kind of meristematic action, newly reported for Gnetum, is produced by proliferation of axial parenchyma, fragmenting secondary xylem. Both presence of tori and site of origin of lateral meristematic activity in Gnetum contrast with corresponding conditions in Welwitschia.     

Stem anatomy of the dwarf subshrub Cressa cretica L. (Convolvulaceae)

Stem anatomy and development of medullary phloem are studied in the dwarf subshrub Cressa cretica L. (Convolvulaceae). The family Convolvulaceae is dominated by vines or woody climbers, which are characterized by the presence of successive cambia, medullary- and included phloem, internal cambium and presence of fibriform vessels. The main stems of the not winding C. cretica shows presence of medullary (internal) phloem, internal cambium and fibriform vessels, whereas successive cambia and included phloem are lacking. However, presence of fibriform vessels is an unique feature which so far has been reported only in climbing members of the family. Medullary phloem develops from peri-medullary cells after the initiation of secondary growth and completely occupies the pith region in fully grown mature plants. In young stems, the cortex is wide and formed of radial files of tightly packed small and large cells without intercellular air spaces. In thick stems, cortical cells become compressed due to the pressure developed by the radial expansion of secondary xylem, a feature actually common to halophytes. The stem diameter increases by the activity of a single ring of vascular cambium. The secondary xylem is composed of vessels (both wide and fibriform), fibres, axial parenchyma cells and uni-seriate rays. The secondary phloem consists of sieve elements, companion cells, axial and ray parenchyma cells. In consequence, Cressa shares anatomical characteristics of both climbing and non-climbing members. The structure of the secondary xylem is correlated with the habit and comparable with that of other climbing members of Convolvulaceae.     

Stem anatomy and development of successive cambia in Hebanthe eriantha (Poir.) Pedersen: a neotropical climbing species of the Amaranthaceae

Hebanthe eriantha (Poir.) Pedersen, a climbing species of the Amaranthaceae increases in stem thickness by forming successive cambia. The family is dominated by herbaceous species and is constantly under discussion due to its disputed nature of the meristem. In the young stem small alternate segments of vascular cambium cease to divide and new arc of cambium initiates outside to it. The newly formed arcs connect with pre-existing alternate segments of cambium to complete the ring. On the contrary, in thick stems, instead of small segments, complete ring of cambium is replaced by new one. These new alternate segments/cambia originate from the parenchyma cells located outside to the phloem produced by previous cambium. Cambium is storied and exclusively composed of fusiform initials while ray cells remain absent at least in the early part of the secondary growth. However, large heterocellular rays are observed in 15-mm diameter stems but their frequency is much lower. In some of the rays, ray cells become meristematic and differentiate into radially arranged xylem and phloem elements. In fully grown plants, stems are composed of several successive rings of secondary xylem alternating with secondary phloem. Secondary xylem is diffuse-porous and composed of vessels, fibres, axial parenchyma while exceptionally large rays are observed only in the outermost regions of thick stems. Vessel diameter increases progressively from the centre towards the periphery of stems. Although the origin of successive cambia and composition of secondary xylem of H. eriantha remains similar to other herbaceous members of Amaranthaceae, the occurrence of relatively wider and thick-walled vessels and large rays in fully grown plants is characteristic to climbing habit.     

Wood and stem anatomy of woody Amaranthaceae s.s.: ecology, systematics and the problems of defining rays in dicotyledons

Wood and stem anatomy is studied for seven species of six genera (root anatomy also reported for one species) of Amaranthaceae s.s. Quantitative data on vessels correlate closely with relative xeromorphy of respective species, agreeing with values reported for dicotyledons without successive cambia in comparable habitats. Libriform fibre abundance increases and vessel diameter decreases as stems and roots of the annual Amaranthus caudatus mature. Long, thick-walled fibres in Bosea yervamora may be related to the upright nature of elongate semi-climbing stems. Non-bordered or minutely bordered perforation plates characterize Amaranthaceae, as they do most other Caryophyllales. Amaranthaceae have idioblastic cells containing druses, rhomboidal crystals or crystal sand: these forms intergrade and seem closely related. Rays are present in secondary xylem of the Amaranthaceae studied. Cells intermediate between ray cells and libriform fibres occur in Charpentiera elliptica . Degrees of diversity in rays and reports of raylessness in Amaranthaceae induce discussion of definition and identification of rays in dicotyledons; some sources recognize both rays and radial plates of conjunctive tissue in Amaranthaceae. The action of successive cambia is described: lateral meristem periclinal divisions produce secondary cortex externally, conjunctive tissue internally and yield vascular cambia as well. Vascular cambia produce secondary phloem and secondary xylem, in both ray and fascicular zones, as in a dicotyledon with a single cambium. Identification of meristem activity and appreciation of varied ray manifestations are essential in understanding the ontogeny of stems in Amaranthaceae (which have recently been united with Chenopodiaceae).  © 2003 The Linnean Society of London, Botanical Journal of the Linnean Society , 2003, 143 , 1–19.     

EFFECTS OF TREE AGE ON SECONDARY XYLEM AND PHLOEM ANATOMY IN STEMS OF GREAT BASIN BRISTLECONE PINE (PINUS LONGAEVA)

Xylem and phloem tissue samples were collected from various-aged Great Basin bristlecone pine (Pinus longaeva D. K. Bailey) stems in southern Utah and southeastern California to determine whether the vascular cambia of older trees produce fewer xylem rays, shorter-lived xylem and phloem ray cells, fewer phloem sieve cells, and a thinner phloem. Increment cores were examined to determine whether ‘aged’ cambia produced narrower tracheids that might reduce water translocation. Sapwood thickness was measured and sapwood growth layers were counted on these cores. Regression and Classification and Regression Tree (CART) analyses of sample data found no age-related changes in cambial products. Phloem and xylem production appeared normal at all ages, with no evidence of cambial malfunction.     

Wood Anatomy and the Development of Interxylary Phloem of Ipomoea hederifolia Linn. (Convolvulaceae)

In Ipomoea hederifolia Linn., stems increase in thickness by forming successive rings of cambia. With the increase in stem diameter, the first ring of cambium also gives rise to thin-walled parenchymatous islands along with thick-walled xylem derivatives to its inner side. The size of these islands increases (both radially and tangentially) gradually with the increase in stem diameter. In pencil-thick stems, that is, before the differentiation of a second ring of cambium, some of the parenchyma cells within these islands differentiate into interxylary phloem. Although all successive cambia forms secondary phloem continuously, simultaneous development of interxylary phloem was observed in the innermost successive ring of xylem. In the mature stems, thick-walled parenchyma cells formed at the beginning of secondary growth underwent dedifferentiation and led to the formation of phloem derivatives. Structurally, sieve tube elements showed both simple sieve plates on transverse to slightly oblique end walls and compound sieve plates on the oblique end walls with poorly developed lateral sieve areas. Isolated or groups of two to three sieve elements were noticed in the rays of secondary phloem. They possessed simple sieve plates with distinct companion cells at their corners. The length of these elements was more or less similar to that of ray parenchyma cells but their diameter was slightly less. Similarly, in the secondary xylem, perforated ray cells were noticed in the innermost xylem ring. They were larger than the adjacent ray cells and possessed oval to circular simple perforation plates. The structures of interxylary phloem, perforated ray cells, and ray sieve elements are described in detail.     

ANOMALOUS GROWTH AND VEGETATIVE ANATOMY OF SIMMONDSIA CHINENSIS

The anatomy of the stem, root, and leaf of Simmondsia chinensis (Link) Schneider was investigated, as well as the mode of tissue formation in the stem. Perivascular tissue is present as part of the primary body; outermost cell layers of this tissue mature as a fibrous sheath. The first short-lived extrafascicular cambium is generated within the remaining parenchymatous perivascular tissue. Successive independent extrafascicular cambia, organized as complete rings or large arcs, arise within peripheral conjunctive parenchyma produced by previous cambia. Extrafascicular cambia produce secondary xylem centripetally and conjunctive tissue bands and strands of secondary phloem centrifugally. Conjunctive tissue initials produce raylike structures of conjunctive tissue; true vascular rays are absent. The phellogen is actually a region of transition where the peripheral conjunctive parenchyma of previous extrafascicular cambia undergoes further cellular subdivision; a true phellogen is lacking. Xylem bands do not represent annual or seasonal growth increments, and secondary growth in Simmondsia is an unequivocal example of the “concentric” anomaly.     

药用植物川牛膝根中异常次生结构的发育解剖学研究

药用植物川牛膝的根内具有异常的次生结构。其异常的次生生长是由维管柱外围发生的异常形成层通过正常的活动方式完成的。后一轮异常形成层起源于前一轮异常形成层向外产生的薄壁组织细胞,位于韧皮部的外侧。每一轮异常形成层向内产生木质部,向外产生韧皮部,组成异常维管束。其中,木质部最先开始分化。异常维管束排成螺旋状,分散在结合组织中。除最外轮一些木质部束之间的结合组织是厚壁组织外,其余结合组织都是薄壁的。由于初生结构和早期的次生结构是正常的,所以,这种异常结构可能是后起的特征。     

Radial secondary growth and formation of successive cambia and their products in Ipomoea hederifolia L. (Convolvulaceae)

Ipomoea hederifolia stems increase in thickness using a combination of different types of cambial variant, such as the discontinuous concentric rings of cambia, the development of included phloem, the reverse orientation of discontinuous cambial segments, the internal phloem, the formation of secondary xylem and phloem from the internal cambium, and differentiation of cork in the pith. After primary growth, the first ring of cambium arises between the external primary phloem and primary xylem, producing secondary phloem centrifugally and secondary xylem centripetally. The stem becomes lobed, flat, undulating, or irregular in shape as a result of the formation of both discontinuous and continuous concentric rings of cambia. As the formation of secondary xylem is greater in one region than in another, this results in the formation of a grooved stem. Successive cambia formed after the first ring are of two distinct functional types: (1) functionally normal successive cambia that divide to form secondary xylem centripetally and secondary phloem centrifugally, like other dicotyledons that show successive rings, and (2) abnormal cambia with reverse orientation. The former type of successive rings originates from the parenchyma cells located outside the phloem produced by previous cambium. The latter type of cambium develops from the conjunctive tissue located at the base of the secondary xylem formed by functionally normal cambia. This cambium is functionally inverted, producing secondary xylem centrifugally and secondary phloem centripetally. In later secondary growth, xylem parenchyma situated deep inside the secondary xylem undergoes de‐differentiation, and re‐differentiates into included phloem islands in secondary xylem. © 2008 The Linnean Society of London, Botanical Journal of the Linnean Society, 2008, 158 , 30–40.     

药用植物商陆(Phytolacca acinosa Roxb.)根中异常次生结构的发育解剖学研究

本文报道了药用植物商陆根中异常次生结构的发生和发育过程。商陆根的初生结构和早期的次生结构都是正常的。但是,后来在维管柱的外围以离心的顺序先后产生5-7轮异常形成层.第一轮异常形成层起源于次生韧皮薄壁细胞和射线细胞。后一轮异常形成层在前一轮异常形成层向外产生的薄壁结合组织中发生。各轮异常形成层都以正常的活动方式产生同心环状排列的异常维管束以及它们之间丰富的薄壁结合组织,从而使根变成肉质状。薄壁结合组织细胞以及异常维管束内的薄壁组织细胞中贮藏有淀粉粒。     

罗汉果营养器官的结构

1.罗汉果根、茎、叶的结构与葫芦科其它植物大致相似。不同之处有三方面:(1)叶子主脉中维管束为5个;(2)叶子中有硅质细胞成群分布;(3)块根具异常次生生长。在次生木质部中围绕导管形成形成层,由之分化出多个具韧皮部与木质部的小维管束。2.叶中的硅质细胞分布于表皮、栅栏组织、海绵组织中,多个细胞集合在一起。其细胞壁加厚并硅质化,细胞内容物消失。推测与增加叶子的支持力量有关。3.罗汉果雌株叶子上、下表皮气孔数之比为0.04,雄株为0.03,比值均很低,同时根据叶的解剖结构推测罗汉果为C_3植物。4.雌株叶子下表皮单位面积气孔数比雄株的多26％,差异很显著,值得进一步研究简化观察统计方法,以用于鉴别幼苗的性别。     

六盘山鸡爪大黄根蒽醌类化合物组织化学定位的研究

采用组织化学方法研究了六盘山鸡爪大黄根蒽醌类化合物的组织化学定位特征及贮藏和积累的规律。结果表明：蒽醌类化合物在根内的贮藏是多位点的,在根周皮的木栓层和栓内层、次生维管组织的维管射线和根中央的部分木薄壁细胞内不同程度地贮藏和积累了一定数量的蒽醌类化合物,次生木质部的木射线和次生韧皮部的韧皮射线是主要贮藏和积累的部位,早期形成的维管射线中蒽醌类化合物的含量较晚期形成的射线含量高。     

Stem anatomy and development of inter- and intraxylary phloem in Leptadenia pyrotechnica (Forssk.) Decne. (Asclepiadaceae)

Modification of external morphology and internal structure of plants is a key feature of their successful survival in extreme habitats. They adapt to arid habitats not only by modifying their leaves, but also show several modifications in their conducting system. Therefore, the present study is aimed to investigate the pattern of secondary growth in Leptadenia pyrotechnica (Forssk.) Decne., (Asclepiadaceae), one such species growing in Kachchh district, an arid region of Gujarat State. A single ring of vascular cambium, responsible for radial growth, divided bidirectionally and formed the secondary xylem centripetally and the phloem centrifugally. After a short period of secondary xylem differentiation, small arcs of cambium began to form secondary phloem centripetally instead of secondary xylem. After a short duration of such secondary phloem formation, these segments of cambium resumed their normal function to produce secondary xylem internally. Thus, the phloem strands became embedded within the secondary xylem and formed interxylary phloem islands. Such a recurrent behavior of the vascular cambium resulted in the formation of several patches of interxylary phloem islands. In thick stems the earlier formed non-conducting interxylary phloem showed heavy accumulation of callose on the sieve plates followed by their crushing in response to the addition of new sieve elements. Development of intraxylary phloem is also observed from the cells situated on the pith margin. As secondary growth progresses further, small arcs of internal cambium get initiated between the protoxylem and intraxylary phloem. In the secondary xylem, some of the vessels are exceptionally thick-walled, which may be associated with dry habitats in order to protect the vessel from collapsing during the dryer part of the year. The inter- and intraxylary phloem may also be an adaptive feature to prevent the sieve elements to become non-conducting during summer when the temperature is much higher.     

Wood, bark and stem anatomy of New World species of Gnetum

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.     

Graniferous tracheary elements in haustoria of root parasitic angiosperms

Graniferous tracheary elements are unusual xylem conducting cells, characterized by having structural material in the lumen. They are known particularly from certain root parasitic angiosperms. The included material is usually granular but may also be amorphous or fibrillar, all having the same origin during differentiation of the tracheary element. Vessels and tracheids with such inclusions were first reported in 1895 by Heinricher inLathraea (Scrophulariaceae). During the early decades of this century graniferous tracheary elements were noted in a few other taxa by different workers but were largely forgotten until the early 1960’s. This paper reviews the early literature and the research carried out during the past twenty-five years on these peculiar cells. Graniferous tracheary elements are found typically in the body of the haustorium of the root parasite, especially in the expanded xylem tissue or “vascular core.” The cells are most widely documented for the hemi-parasitic Santalaceae and were first recorded there in 1910 by Benson. She named the cells “phloeotracheides,” believing they combined the functions of phloem and xylem conducting elements. Heinricher and Benson both considered the granules to be composed of amylodextrin starch and Benson also believed the cells contained an enucleated protoplast. Our work has demonstrated that the granules in the Santalaceae are proteinaceous and that the cells are dead at maturity. In 1978 we therefore renamed them “graniferous tracheary elements.” They occur in all species of the Santalaceae so far investigated and inAtkinsonia ligustrina andNuytsia floribunda of root parasitic Loranthaceae. In these two families graniferous tracheary elements have the same organization. Their occurrence in haustoria of root parasites from other families is also reviewed. Although few observations are yet available in the Olacaceae, the granules inXimenia americana are found to be starch grains, like those inLathraea, whereas those inOlax phyllanthi are protein. Such fundamentally different material in haustorial tracheary elements within the same taxonomic group naturally raises the question of relationships within the family. The function of graniferous tracheary elements has not been experimentally investigated but we have suggested that for some Santalaceae they might serve as a device for regulating the flow of xylem sap through the haustorium.     

SUCCESSIVE CAMBIA IN THE STEM OF PHYTOLACCA DIOICA

Phytolacca dioica L., an evergreen tree of the Phytolaccaceae, is one of the species of Phytolacca which shows anomalous secondary thickening in its stem. This mode of thickening has been regarded as successive cambial activity or alternatively, in some more recent interpretations, as thickening by unidirectional activity of a cambial zone. The stem thickening of P. dioica is of the former type. The cambium produces fascicular strands, showing centrifugal differentiation of xylem and centripetal differentiation of phloem on opposite sides of the cambial layer, and rays are produced between the fascicular areas. In both xylem and phloem the younger elements are closer to the cambium than the older elements. Succeeding cambia arise periodically by periclinal divisions in a layer of parenchyma cells two or three cells beyond the outermost intact phloem derived from the current cambium. Each cambium forms a few parenchyma cells on both sides before it forms derivatives which mature into lignified xylem elements or conductive elements of the phloem. The parenchyma thus formed toward the outside later becomes the site of the origin of the succeeding cambium. Only one or two layers of this phloem parenchyma go on to form the new cambium; the remaining cells accumulate between the outermost phloem and the cortex. P. weberbaueri shows stem structure similar to P. dioica. P. meziana, a shrub, shows normal stem structure.     

ANATOMY OF NODES VS. INTERNODES IN COLEUS: THE NODAL CAMBIUM

Secondary growth begins in the nodal regions before the internodal regions in Coleus, so that longitudinally discontinuous vascular cambia are formed in the 6th through the 9th or 10th nodes, where the internodal cambium becomes continuous between nodal cambia. The nodal cambia are identifiable by radial seriation in interfascicular regions, typical cytology of fusiform initials, and the presence of a ray system. Anatomical features distinct from the primary plant body are shared by the nodal and internodal cambia. Branching of primary vascular strands, restricted to procambium and phloem, is virtually confined to nodal regions. In secondary growth, vascular branching of xylem and phloem occurs in both nodes and internodes. Xylem strand branches are formed only from derivatives of vascular cambia. It is proposed that the cambium provides the secondary plant body an efficient channel for lateral auxin transport, by which branching across interfascicular regions is facilitated.     

Vascular Continuity in the Primary and Secondary Stem Tissues of Bougainvillea (Nyctaginaceae)

An investigation of stem structure of Bougainvillea by serialsections and cine-photography shows that the medullary systemof the inner area of young stems is the sole vascular systemdirectly continuous into the lateral appendages (leaves, axillarybuds and axillary thorns) via complex nodal anastomoses. Thevascular system at the periphery of the primary bundles is notdirectly continuous into these appendages. In secondary growth,there is direct continuity between vascular bundles within asingle ring, in a tangential direction via either xylem aloneor both xylem and phloem, and between rings in a radial directionalways via xylem and phloem, even though the rings are derivativesof successive cambia. Bougainvillea, vascular system, phloem, xylem, anomalous secondary thickening