摘要:

FANNING, U., EDWARDS, D.&RICHARDSON, J. B., 1992.A diverse assemblage of early land plants from the Lower Devonian of the Welsh Borderland.Nine rhyniophytoid taxa are described from an early Gedinnian locality (middle micromatus‐newportensisspore Biozone) near Ludlow, England. They includeCooksonia pertoni, C. hemisphaerica, C. cambrensis, Tortilicaulis transwalliensisand three new taxa,Salopella marcensissp. nov.,Uskiella reticulatasp. nov.andTarrantia salopensisgen. et sp. nov.Isolated sporangia of reniform shape, and those subtended by short lengths of axis, contain spores ofApiculiretusisporatype and may belong toC. caledonicaorRenalia. Morphologically distinctive forking, terminal sporangia lacking identifiable spores are not placed in a new taxon, because evidence based onin situspores from elsewhere suggests they may belong toSalopella. Structures previously interpreted as clusters of sporangia ofYarravia‐type are shown to be ± globular sporangia longitudinally split into valves. Sterile axes are dominated by smooth forms; although rare examples possess small enations. Tracheids have not been seen in axes of fertile specimens nor in sterile coalified compressions. A single pyrite permineralization contains tracheids of zosterophyll type. The assemblage demonstrates diversity among rhyniophytoids in the early Devonian and the existence of low vegetation ‘alongside’ the much larger zosterophyll domina

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb00264.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

SHOU‐GANG, H., 1992.Some observations onZosterophyllutn australianumLang&Cookson from the Lower Devonian of Yunnan, China.Recent collections ofZosterophyllum australianumhave been made from the Xujiachong Formation which outcrops near Xujiachong village in the Qujing district of Yunnan province. The unit is a non‐marine facies of the type section of the Lower Devonian of China. Sediments containing the fossil material are probably Siegenian‐Emsian in age. Details of the morphology of fertile spike ofZ. australianumare recorded. The spikes bear short‐stalked, rather large, transversely elliptical sporangia, each with a wide, thickened, distal border. Sporangia are borne close together in a dextrorse helix, and usually in four or five longitudinal rows. Morphological variation of in‐situ spores is also described. Comparison of the new specimens with others of reportedZ. australianumhas led to some nomenclatura

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb00265.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

LOURO, R. P., MIGUENS, F. C.&MACHADO, R. D., 1992.Structure and development of stellate trichomes inAndradea ftoribundaFr. Allem. (Nyctaginaceae).Trichomes occur on both faces of young leaves. They are peltate‐stellate on the abaxial face, and comprise a stalk and radiating cells with a rudimentary central apex. On the adaxial face the trichomes arc stellate with a large apex comprising one to three cells. In both cases the stalk is formed by three to six cells of which the most distal may contain a tannoid substance. In the adult leaf only the abaxial surface exhibits stellate trichomes, with two to three celled stalks. The central region of radial cells is depressed. On the adaxial side the hairs are shed during maturation of the lea

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb00266.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AJMAL, S.&IQBAL, M., 1992.Structure of the vascular cambium of varying age and its derivative tissues in the stemof Ficus rumphiiBlume.The cambial cells ofFicus rumphiiand their derivatives vary in size and number with the age of the tree. The fusiform initials, vessel elements, sieve‐tube members, xylem fibres and phloem fibres are relatively short in the terminal part of the stem axis, consistently longer down the stem reaching a maximum, and short again in the main trunk. The width of the respective cells shows a similar variation. The ray cell initials increase both in number and size, and form rays of varying dimensions. Uniseriate and biseriate cambial rays are abundant, while multiseriate rays are especially sparse in the young shoot. The proportion of uni‐ and biseriate rays falls in the lower part of the stem whereas that of multiseriate rays increases. Likewise, short cambial rays are abundant in young branches but their frequency decreases in the trunk region, leading to a rise of the tall ray population. The rays in the phloem and xylem regions reflect a similar variation pattern with certain fluctuations. The overall proportion of the rays increases in the older part of the axis, reaching a maximum tangential area in the trunk. The transectional area of vessel elements remains more or less constant down to the base after an initial increase in the terminal region, while the sieve‐tube proportion tends to be constant in the basal region after a consistent gain from the tree top base

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb00267.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

COWGILL, U. M.&LANDENBERGER, B.D., 1992.The chemical composition ofAstragalus:a comparison of seleniferous and non‐seleniferous plants growing side by side.This paper describes how non‐seleniferous plant species coexist with seleniferous ones and what chemical changes occur in non‐seleniferous species that allow the toleration of large quantities of volatilized Se‐bearing compounds. These compounds are known for their phytotoxicity as well as for their toxicity to mammals and insects. Twenty‐three sites (Colorado, Utah, New Mexico, U.S.A.) were examined over a 6‐year period. Plants collected from these sites were divided into four groups: seleniferous astragali, seleniferous Brassicaceae, non‐seleniferous astragali and non‐seleniferous associated genera. Furthermore, it was possible to categorize these sites: Type 1 sites supported all four groups of plants, Type 2 sites contained only seleniferous astragali, whereas Type 3 sites sustained only non‐seleniferous astragali. When concentrations of Cu, Zn (P<0.0001), Si (P<0.02), As, Pb (P<0.03) and Cs (P<0.05) were measured, the values for those seleniferous astragali that coexisted with other species were significantly different from the values found for those seleniferous astragali that grew alone. There were four areas that in some years supported all four groups of plants (Type 1 site) and in other years contained only seleniferous astragali. In this way, the latter may be used as a chemical control for the former. The seleniferous astragali collected at Type 1 sites always contained more Cu, As, Si and Pb than the solitary astragali of Type 2 sites. When seleniferous astragali of Type 1 sites that support all four groups of plants develop in a year where the usually associated species of past years are absent, they contain in their tissues concentrations of Cu, As, Si, Pb, Zn and Cs typical of Type 2 sites where the seleniferous astragali grew alone. Non‐seleniferous astragali of Type 1 sites that support all four groups of plants have a chemical composition that differs significantly in the quantity of 15 elements from non‐seleniferous astragali of Type 3 sites where the latter grew alone. Since allelochemicals such as phenolic acids and flavonoids are well known to be able to alter mineral absorption by plants and since the astragali are known to produce such substances, it is suggested that the possible production of phenolic acids and flavonoids may permit coexistence of seleniferous plants with non‐seleniferous ones and thus explain the chemical differences among the plants of

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb00268.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

WANNAN, B. S.&QUINN, C. J., 1992.Inflorescence structure and affinities ofLaurophyllus(Anacardiaceae).The inflorescence structure, pollen and floral anatomy are investigated inLaurophyllus. The inflorescence is a paniclesensuBriggs&Johnson, but with marked differences between the male and female. Sistergroup comparison with the Burseraceae indicates that the plesiomorphic inflorescence in the Anacardiaceae is a thyrsoid, the apomorph being the panicle.LaurophyllushasRhus‐type pollen and therefore has no close affinity withDobineaorCampylopeialum. Floral anatomy reveals thatLaurophyllusis unicarpellary with a dorsally attached style and an apically attached ovule. These characters suggest that rather than being related toAnacardiumorMangifera, it has some affinity withBlepharocaryaor perhaps with one of the poorly known African or Madagascan gener

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb00269.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

AKIYAMA, S., WAKABAYASHI, M.&OHBA, H., 1992.Chromosome evolution in HimalayanImpatiens(Balsaminaceae).Chromosome numbers and karyotypes have been investigated in species of HimalayanImpatiens. In addition to confirming previous chromosome counts, the presence of a tetraploid taxon (I. exilis)is revealed. In central and east Nepal species withx= 9 are more common than those with other basic numbers and this number is shown to be one of the most frequent numbers in the genus. Most species withx= 9 have a bimodal karyotype. The species relationships are discussed.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb00270.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

CHARLTON, W. A., 1992.The rachis‐leaves ofLilaeopsis brasiliensis(Glaziou) J. M. Affolter.The leaves ofLilaeopsis brasiliensishave the general features of the terete linear rachis‐leaves which have been described in other umbellifers. The leaf consists of a septate structure which appears to correspond to the rachis of compound umbellifer leaves, and at some of the septa a single hydathode is inserted on the adaxial midline of the leaf. The septa appear to correspond to the positions of pinna insertion in compound leaves, and the hydathodes to reduced pinnae. Although by these criteria the leaf ofL. brasiliensisis a rachis‐leaf, it differs from most other umbellifer rachis‐leaves in presenting the appearance of a petiole and a dorsiventrally flattened leaf blade. As in other rachis‐leaves of umbellifers which have been examined previously, the leaf arises from a leaf primordium which is initially dorsiventral in symmetry. However, the leaf ofL. brasiliensisis distinctive in that it retains dorsiventral symmetry throughout development, while it also acquires the median hydathodes and a vascular system characteristic of ‘unifacial’ rachis‐leaves. The leaf therefore shows a mixture of features which are not normally associated. It provides an argument for the restriction of the term ‘unifacial’ to a solely descriptive role without developmental implications. Simplification of the structure in the distal region of the blade results in an appearance close to that of a normal dorsiventral leaf, though a small number of inverted vascular bundles remain. This may indicate the occurrence of further evolutio

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb00271.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

COX, P. A., LAUSHMAN, R. H.&RUCKLESHAUS, M. H., 1992.Surface and submarine pollination in the seagrassZostera marinaL.Hydrophilous plants can be divided into three ecological categories depending upon whether their pollen is transported above, on, or under the water surface. A mixed mode of submarine and surface hydrophilous pollination occurs in the seagrassZostera marinaL. In the surface mode of pollination, pollen rafts or ‘search vehicles’ which superficially resemble snowflakes, form at low tide and are transported on the surface of the sea by winds and water currents. Some of the search vehicles collide with the floating female stigmas, effecting pollination. In the submarine mode of pollination, small pollen masses resembling whisk brooms travel beneath the surface of the water. Although we failed to observe a submarine pollination event, SEM analysis of stigmas from subtidal populations confirms that submarine pollination does occur inZ. marina. However, observations of stigmas positioned at and below the surface of the water show surface pollination to be highly efficient. Electrophoretic evaluation of both subtidal and intertidal populations indicates significant genetic variation between populations. Given the high flux rates of surface‐borne pollen and pollen viability in excess of 5 h, it is likely that surface‐borne pollen is a major source of gene flow inZostera marinapopu

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb00272.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY

摘要:

VAN RAAMSDONK, L. W. D., WIETSMA, W. A.&DE VRIES, J. N., 1992.Crossing experiments inAlliumL. sectionCepa.A full diallel was carried out with six diploid species ofAlliumsectionCepaandA. royleiof sectionRhizirideum, High isolation barriers were found between the related speciesA. cepaandA. oschaninii, betweenA. oschaniniiandA. vavilovii, and betweenA. galanthumandA. pskemense. On the contrary, the speciesA. cepaandA. roylei, belonging to different sections, show only slight isolation barriers. The Wallace effect, which is the development of internal isolation barriers as such, is likely to have taken place in the evolution ofA. oschaniniiandA. vavilovii, and possibly also betweenA. galanthumandA. pskemense.

ISSN:0024-4074    

DOI:10.1111/j.1095-8339.1992.tb00273.x

出版商:Blackwell Publishing Ltd    

年代:1992

数据来源: WILEY