Starch Grain Casts and Moulds in Eocene (Tertiary) Fossil Mangrove Hypocotyls

Further examples of the recently reported fossil starch graincasts and moulds in the fossil mangrove Ceriops cantiensis Chandlerfrom the London Clay (Eocene) of the Isle-of-Sheppey, Kent,England have now been discovered. In addition, similar structureshave been found in the fossil hypocotyls of Palaeobruguieraelongata Chandler from Herne Bay, Kent and also in four recentlycollected hypocotyls of a new species of fossil mangrove fromSheppey. Starch grains from herbarium material of the extantmangrove genera, Bruguiera and Ceriops, have been examined forcomparison with the fossil forms. starch grain casts, fossil, mangrove, hypocotyls, palaeobotany, Eocene, framboids, Rhizophoraceae, Bruguiera sexangula, Ceriops cantiensis, Palaeobruguiera elongata     

Evidence of polar auxin flow in 375 million-year-old fossil wood

In living woody seed plants (conifers and dicotyledons), when various obstacles such as buds and branches disrupt the axial polar auxin flow, auxin whirlpools are formed that induce the differentiation of circular tracheary elements in the secondary xylem. Identical circular patterns also occur at the same positions in the wood of the 375 million-year-old Upper Devonian fossil progymnosperm Archaeopteris. We propose that this is the earliest clear fossil evidence of polar auxin flow. Such spiral patterns do not occur in the primary xylem of the ca. 390-385 million-year-old Lower Devonian fossil land plants, fossil progymnosperms, Psilotum nudum, living ferns, and current seed plants that we examined. This discovery reveals an exciting potential for plant fossils to provide structural evidence of evolutionarily diagnostic physiological and developmental mechanisms and for the use of a combination of fossil evidence and developmental biology to characterize evolutionary patterns in terms of genetic changes in growth regulation.     

Palaeontological evidence of membrane relationship in step-by-step membrane fusion

Studies on membrane fusion in living cells indicate that initiation of membrane fusion is a transient and hard to capture process. Despite previous research, membrane behaviour at this point is still poorly understood. Recent palaeobotanical research has revealed snapshots of membrane fusion in a 15-million-year-old fossil pinaceous cone. To reveal the membrane behaviour during the fusion, we conducted more observations on the same fossil material. Several discernible steps of membrane fusion have been fixed naturally and observed in the fossil material. This observation provides transmission electron microscope (TEM) images of the transient intermediate stage and clearly shows the relationship between membranes. Observing such a transient phenomenon in fossil material implies that the fixing was most likely accomplished quickly by a natural process. The mechanism behind this phenomenon is clearly worthy of further enquiry.     

Protoxylem: the deposition of a network containing glycine-rich cell wall proteins starts in the cell corners in close association with the pectins of the middle lamella

Antibodies were used to localise polysaccharide and protein networks in the protoxylem of etiolated soybean (Glycine max L.) hypocotyls. The deposition of glycine-rich proteins (GRPs) starts in the cell corners between protoxylem elements and xylem parenchyma cells. Finally, the GRPs form a network between two mature protoxylem elements. The network also interconnects the ring- and spiral-shaped secondary wall thickenings, as well as the thickenings with the middle lamellae of living xylem parenchyma cells. In addition to the GRP network, a polysaccharide network composed mainly of pectins is involved in the attachment of the secondary wall thickenings to the middle lamellae of xylem parenchyma cells.     

A palaeobiological examination of the geological evidence for recurring outbreaks of the crown-of-thorns starfish,Acanthaster planci (L.)

Geological investigations of the crown-of-thorns starfish (COTS) have concluded that outbreaks are not only recent but also have occurred in the past. The evidence lies in the abundance of COTS skeletal elements found both on the sea floor and within the underlying sedimentary record. These studies are flawed in three respects. First, the processes of fossil preservation from the living population to the fossil assemblage have been ignored. Second, it has not been demonstrated that the fossil skeletal elements representing alleged outbreak populations of starfish are of the same age. Third, the existence of a relationship between the number of COTS skeletal elements sampled from the sedimentary record and the relative abundance of COTS in the once living population has not been substantiated. The limitations introduced when studying the fossil record need to be established through taphonomic analyses of the COTS. Techniques which will allow greater temporal resolution of skeletal element age include amino-acid geochronology, analysis of sedimentation mode and rate, and correlation among sub-surface cores. In order to establish a relationship between the number of fossil COTS elements and the original population size, methods must be developed which will relate the number of fossil skeletal elements to the relative abundance of starfish in both the fossil and death assemblages and then to relate the latter to the relative size of the original population. When these approaches are used together it may be possible to make some estimate of relative COTS abundances based on data contained in the fossil record.     

New records of Early Cretaceous petrified wood in Yumen,northwestern Gansu Province,China and their palaeoclimatic implications

Several fossil woods from Early Cretaceous sediments in Yumen City in northwestern North China Block, China, have been described. They belong to two fossil wood taxa, Piceoxylon yumeniense Zhou, Peng, Deng, Zhang and Yang n. sp. and Protophyllocladoxylon chijinense Zhou, Peng, Deng, Zhang and Yang n. sp. The well-preserved specimens yield secondary xylem with distinct growth rings. Piceoxylon yumeniense exhibits cross-field with taxodioid pits as well as two distinct xylem ray types. The bi- to triseriate rays are characterised by one or two horizontal resin canals with unequal uniseriate ends. Protophyllocladoxylon chijinense Zhou, Peng, Deng, Zhang and Yang n. sp. shows window-like cross-field pits, which are occasionally cupressoid and have uniseriate xylem rays. These fossil wood records improve our understanding of the fossil diversity, floral composition and palaeoclimate of the Xiagou Formation. Palaeoclimatic analysis of the palaeoxylogical assemblage indicates that the northwestern Gansu region predominantly exhibited a warm and wet climate condition, while a brief cooling event may have occurred in the region during the Early Cretaceous.     

Ion-mediated changes of xylem hydraulic resistance in planta: fact or fiction?

Although xylem provides an efficient transport pathway for water in plants, the hydraulic conductivity of xylem (K(h)) can still influence plant water status. For decades, the K(h) of functional xylem has been assumed to be constant in the short term because xylem consists of a network of dead interconnected capillary elements (conduits). Recent research has shown that K(h) can change in response to the cation content of the xylem fluid. Volume changes of pectin gel in nanometer-sized pores at inter-conduit connections are hypothesized to be the cause, and implications for xylem transport in planta are suggested. However, it seems too early to be conclusive about this phenomenon because the phenomenon has not been measured in planta with xylem fluids that realistically mimic natural xylem sap and the applied methods used to measure ion-mediated changes in K(h) have drawbacks.     

PHLOEM ANATOMY IN STAUROPTERIS BISERIATA FROM THE PENNSYLVANIAN OF NORTH AMERICA

Phloem anatomy in the coenopterid fern Stauropteris biseriata is detailed from Lower-Middle Pennsylvanian coal ball specimens from eastern Kentucky. Axes exhibit a cruciate-shaped xylem trace in transverse section. Phloem tissue completely surrounds the xylem, but is more extensively developed in the embayments between the xylem arms. Phloem is composed of elongate conducting elements with a few scattered parenchyma cells. Large and small sieve cells are present, with larger ones occurring in the embayments within the primary plane of symmetry of the axes. Large elements are approximately twice the diameter of the smaller sieve elements. Oval sieve areas and pores have been observed on lateral and oblique end walls of both large and small elements. The structure and composition of Stauropteris phloem is discussed in relationship to the available information on phloem anatomy in other fossil cryptogams.     

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.     

Development and Structure of the Haustorium of the Parasite Rhamphicarpa fistulosa (Scrophulariaceae)

Rhamphicarpa fistulosa (Hochst.) Benth. (Scrophulariaceae), a parasite of African cereals, develops secondary haustoria which penetrate the roots of the host plant. Light and electron microscopy have been used to study the structure and development of haustoria in this species, which, until now, have not been well characterized. Haustoria are initiated in the hypodermis of the parasite roots. A meristematic strand is developed between the parasite root stele and the host-parasite interface. From this strand, cells differentiate into xylem elements after penetration of the host root. Xylem differentiation follows an acropetal pattern. Mature haustoria are characterized by a continuous xylem bridge between water conducting elements of parasite and host. A detailed study of the hostparasite interface revealed the presence of collapsed and compressed host cells at the lateral interface (between parasite cells and host cortex), whereas the central interface between parasite cells and the host stele is almost devoid of host cell remnants. Implications of these observations for the penetration mechanisms are discussed.     

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.     

Todea from the Lower Cretaceous of western North America: implications for the phylogeny, systematics, and evolution of modern Osmundaceae

The first fossil evidence for the fern genus Todea has been recovered from the Lower Cretaceous of British Columbia, Canada, providing paleontological data to strengthen hypotheses regarding patterns of evolution and phylogeny within Osmundaceae. The fossil consists of a branching rhizome, adventitious roots, and leaf bases. The dictyoxylic stem has up to eight xylem bundles around a sclerenchymatous pith. Leaf traces diverge from cauline bundles in a typical osmundaceous pattern and leaf bases display a sheath of sclerenchyma around a C-shaped xylem trace with 2-8 protoxylem strands. Within the adaxial concavity of each leaf trace, a single sclerenchyma bundle becomes C-shaped as it enters the cortex. The sclerotic cortex is heterogeneous with an indistinct outer margin. The discovery of Todea tidwellii sp. nov. reveals that the genus Todea evolved by the Lower Cretaceous. A phylogenetic analysis combining morphological characters of living and extinct species with a previously published nucleotide sequence matrix confirms the taxonomic placement of T. tidwellii. Results also support the hypothesis that Osmunda s.l. represents a paraphyletic assemblage and that living species be segregated into two genera, Osmunda and Osmundastrum. Fossil evidence confirms that Osmundaceae originated in the Southern Hemisphere during the Permian, underwent rapid diversification, and species extended around the world during the Triassic. Crown group Osmundaceae originated by the Late Triassic, with living species appearing by the Late Cretaceous.     

Function of transfer cells in the nodal regions of stems,particularly in relation to the nutrition of young seedlings

Summary The distribution and time course of development of transfer cells in the hypocotyl region of lettuce (Lactuca sativa L.) and groundsel (Senecio vulgaris L.) are examined by light microscopy of serial sections through a sequence of ages of hypocotyls. Investments of xylem transfer cells occur in departing traces to the cotyledons and, later, in the traces to foliage leaves; phloem transfer cells are widely distributed but particularly prominent in those bands of protophloem in the plumule vasculature which lie alongside xylem of the cotyledonary traces. Both classes of transfer cell are well endowed with wall ingrowths before differentiation of xylem and perforation of stomata occurs in the plumule. Autoradiographic evidence is obtained of a transport pathway from cotyledonary trace xylem elements to xylem transfer cell to plumule, and analyses of xylem sap collected from above or below the zones of transfer cells in the hypocotyl show that certain materials can be removed from the xylem sap by transfer cells as it moves towards the cotyledons. From these findings it is concluded that the seedling transfer cells play an important role in nutrition of the young plumule, particularly before the latter has become adequately connected with the vascular systems of cotyledons and root.Experiments on the experimental modification of transfer cell development in the hypocotyl suggest that both photosynthetic fixation of carbon dioxide and a transpirational loss of water by a cotyledon must take place before the presumptive xylem transfer cells in its traces can develop normal sets of wall ingrowths.Discussion is extended to the general role of transfer cells in the nodal regions of stems. Possible functions envisaged are, the general nutrition of young tissues of the apical region, the abstraction of assimilates for local storage, the transfer of assimilates to axillary buds released from apical dominance, and the interchange of assimilates between adjacent vascular traces running through the node.     

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.     

Rhyncholites and conchorhynchs as calcified jaw elements in some late Cretaceous ammonites

Conspicuous calcareous coverings are present in the anterior region of 17 fossil jaws from late Cretaceous rocks of Hokkaido (Japan) and Sakhalin (U.S.S.R.). The jaws were preserved in calcareous nodules either in situ in body chambers of ammonites or in close association with identifiable ammonite conch remains. From the morphologic similarity between in situ and isolated jaws, they may be attributed to Tetragonites glabrus, Gaudryceras tenuiliratum, G. denseplicatum, G. sp., and Neophylloceras subramosum. The jaw apparatus of these species is composed of two three-dimensional black walls of carbonate apatite, which might be a diagenetic replacement of chitinous material. The calcareous coverings in both upper and lower jaws closely resemble those of upper (rhyncholite) and lower (conchorhynch) jaws of modern Nautilus as well as rhyncholite and conchorhynch fossils in their gross morphology, microstructure, and chemical composition. Calcified remains of cephalopod jaws known as rhyncholites and conchorhynchs have been reported from late Paleozoic to Recent. The present discovery of ammonoid rhyncholites and conchorhynchs suggests that at least some previously known late Paleozoic and Mesozoic counterparts belong to the Ammonoidea. The essential similarity of jaw elements of some Late Cretaceous ammonites and modern Nautilus gives reliable information on the feeding habits of the former. The sharp and thick ammonoid rhyncholites and conchorhynchs may have had a special function for cutting up food, similar to those of Nautilus.     

Graniferous tracheary elements in the haustorium ofAtkinsonia ligustrina,a root hemi-parasite of theLoranthaceae

Summary The xylem conducting cells that form the vascular core in the root haustorium ofAtkinsonia ligustrina are shown to be graniferous tracheary elements. Their luminal contents occur in the form of granules, amorphous bodies or finely dispersed material derived from the granules. Cells of this type are known for theSantalaceae, but have not previously been reported unequivocally in theLoranthaceae. The matrix of the granules consists of compacted fibrillar material often with the central region of the granule showing a crystalline substructure. The granules stain positively for protein. In some instances the matrix may become secondarily impregnated with phenolic compounds. The granules arise during differentiation of the tracheary element and develop as accumulations of matrix within dilated cisternae of endoplasmic reticulum. The function of graniferous tracheary elements inAtkinsonia may be to help regulate the flow of xylem sap from host to parasite, as has been suggested for theSantalaceae.     

The flora of the early Miocene Brandon Lignite, Vermont, USA. VIII. Caldesia (Alismataceae)

Caldesia, a genus of aquatic monocotyledons, is represented by four living species, which are widely distributed in the temperate and tropical Old World. The genus has an extensive Oligocene through Pleistocene fossil record in Eurasia. We survey the morphology of the extant and fossil fruits of the Alismataceae, and provide a detailed review of the morphology and anatomy of living and fossil Caldesia fruits. The latter exhibit substantial similarity, making the recognition of separate species on the basis of fruit morphology difficult. We erect the new species Caldesia brandoniana from the Early Miocene Brandon Lignite of Vermont primarily on the basis of its geographic isolation; careful revision of all fossil fruiting material of Caldesia might require placement of the Brandon specimens in a more inclusive form species. Together with leaves of Caldesia from the Miocene Clarkia flora of Idaho, this occurrence indicates that Caldesia was in the New World as recently as the Early Miocene.     

TRIPLOCHITIOXYLON (STERCULIACEAE): A NEW GENUS OF WOOD FROM THE EOCENE OF OREGON AND ITS BEARING ON XYLEM EVOLUTION IN THE EXTANT GENUS TRIPLOCHITON

A new sterculiaceous wood, Triplochitioxylon oregonensis gen. et sp. n., was collected from a Middle Eocene locality in the Clarno Formation of Oregon. Anatomical data indicate a close natural relationship between T. oregonensis and the living species of Triplochiton, a genus endemic to tropical Africa. The fossil is believed to represent a population of the group or complex from which Triplochiton evolved. The basic differences in the xylem organizations of the two genera are explained by a significant reduction of fusiform initial length and by a complete suppression of post-cambial parenchyma strand elongation in the extant genus. Paleobotanical and biogeographical evidence suggest that the xylem evolution has been strongly influenced by the increasing aridity of the African continent.     

XYLEM ANATOMY OF SOPHORA (LEGUMINOSAE) IN RELATION TO HABIT

Cumbie , B. G., and Dan Mertz . (U. Missouri, Columbia.) Xylem anatomy of Sophora (Leguminosae) in relation to habit . Amer. Jour. Bot. 49(1): 33–40. Illus. 1962.—A comparison of 8 tree, shrub, and herbaceous species of Sophora showed considerable variation in structural organization of the secondary xylem in relation to habit. A reduction in duration of cambial activity has been accompanied by a decrease in conspicuousness of storied structure, more frequent arrangement of vessels in multiples, the formation of narrower rays, and a striking reduction in amount of axial xylem parenchyma. On the other hand, relatively minor changes in size of xylem elements have resulted from decreased cambial activity, as shown by comparing the first-formed secondary xylem elements of woody and herbaceous species. In many structural features, shrubs were found to be more or less intermediate between the tree and herbaceous species, at least in the early stages of development. These observations indicate that the often repeated generalization that the organization of herbaceous stems resembles that of the first year's growth in closely related woody species is not always applicable.