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     

The Initiation and Development of Secondary Xylem in Axillary Branches of Populus deltoides

The initiation of secondary xylem in elongating axillary branchesof Populus deltoides Bartr. ex Marsh. is independent of thatin the main stem. Although secondary xylem differentiates acropetallyin the main stem, it does not differentiate from the stem intothe axillary branch. Secondary xylem is usually initiated ininternode 4 (occasionally 3) of the axillary branch, and fromthis site it develops both acropetally in the elongating branchand basipetally toward the main stem. Secondary vessel differentiationalways precedes fibre differentiation. Although secondary xylemdifferentiates in internodes that have ceased elongation, itdifferentiates first in traces of the vascular cylinder servingrapidly expanding and maturing foliage leaves. As younger leaveson the branch expand and mature, secondary xylem differentiatesin their traces eventually producing a complete secondary vascularcylinder. Scale leaves do not initiate secondary xylem independentlyin their traces; they are activated by adjacent traces in thevascular cylinder serving foliage leaves. Once established,the primary-secondary vascular transition zone advances acropetallyin a branch just as it does in the main stem. Populus deltoides Bartr. ex Marsh., cottonwood, axillary branches, secondary xylem, plastochron index, post-dormancy development, xylem.     

Comparative Root Anatomy of Five Actinidia Species in Relation to Rootstock Effects on Kiwifruit Flowering

This study examined the root anatomy of five Actinidia specieswhich, when used as rootstocks, differ in their effects on flowerproduction of the 'Hayward' kiwifruit scion. The rootstock speciesexamined were A. hemsleyana, A. eriantha, A. rufa, A. deliciosaand A. chinensis. Roots of all the five species had similartissues and similar cell types in each tissue. The cortex andendodermis were retained and developed further during secondaryroot thickening. Each meriphyte of endodermal cells, derivedduring secondary growth, was enclosed in a suberin lamella.Crystalline idioblasts were present in the cortex and phloem.These idioblasts contained raphide crystals, often surroundedby mucilage. Roots of the five species differed significantlyin the total cross-sectional area of vessels in the xylem, inthe total cross-sectional areas of fibres and crystalline idioblastsin the phloem, and in the abundance of starch grains in parenchymaof all tissues. Roots of flower-promoting rootstock speciestended to have more and larger xylem vessels, more crystallineidioblasts, and more starch grains. These anatomical featuresmay be used as criteria for future selection of flower-promotingrootstocks in kiwifruit. The possible physiological link betweenroot anatomy and rootstock effect is discussed.Copyright 1994,1999 Academic Press Kiwifruit, Actinidia, root, anatomy, rootstock, flowering     

Modification of Leaf Formation by Cytokinin and Chlormequat (CCC) in Vitis

Application of the cytokinin, 6-(benzylamino)-9-(2-tetrahydropyrany1)-9H-purine(PBA, 1mM) and 2-chloroethyl trimethyl ammonium chloride (chlormequat;3 mM), a growth retardant, to grapevines induced the formationof fused leaves (two laminae and two petioles) and double leaves(two separate petioles each with a single lamina). Double leaveswere found in Vitis vinifera L. seedlings, in Vitis ripariaand in Muscadinia (Vitis) rotundifolia. In some of the treatedvines, leaves arose with opposite phyllotaxy. Other anomaliesincluded production of two opposite axillary buds in axils ofopposite leaves and production of two tendrils per node. Sometendrils grew into shoots. In Muscat of Alexandria, applicationof GA₃ (3 µM, 15 µM), followed by an applicationof chlormequat (0.4 mM, 1.2 mM), led to a marked reduction inthe extension growth of axillary shoots. Vitis vinifera L., Vitis riparia, Muscadinia (Vitis) rotundifolia, grapevines, leaf formation, cytokinin, chloromequat     

Development and Structure of the Root Cortex in Caltha palustris L. and Nymphaea odorata Ait.

Structural features of the mature root cortex and its apoplasticpermeability to dyes have been determined for two dicotyledonouswetland plants of differing habitats: Nymphaea odorata, growingrooted in water and mud, and Caltha palustris, growing in temporalwetlands among cattails. In mature roots, movement of the apoplasticdyes, berberine and safranin, into the roots was blocked atthe hypodermis, indicating the presence of an exodermis. A hypodermiswith an exodermis, i.e. Casparian bands in the outermost uniseriatelayer plus suberin lamellae, is present in both species. InN. odorata, hypodermal walls are further modified with cellulosicsecondary walls. Roots of N. odorata and C. palustris have anendodermis with Casparian bands only. A honeycomb aerenchymais produced by differential expansion in N. odorata and includesastrosclereids and diaphragms, while roots of C. palustris haveno aerenchyma, but some irregular lacunae are found in old roots.These aspects of cortex structure are related to an open meristemorganization, with unusual patterns of cell divisions in certainground meristem cells (called semi-regular hexagon cells) ofN. odorata. The correlation between aerenchyma pattern and hypodermalstructure appears to be related to habitat differences.Copyright2000 Annals of Botany Company Caltha palustris, Nymphaea odorata, root development, cortex, endodermis, aerenchyma, exodermis, hypodermis, permeability, wetland plants     

Empirical Models for Xylogenesis in Populus deltoides

Empirical quantitative models were constructed for Populus deltoidesdescribing temporal and spatial changes in vessel characteristicsof metaxylem, both within individual central leaf traces andwithin all central leaf traces considered as a morphologicalunit at a given transverse level in the stem (the central tracesympodia). Similar models were constructed for secondary vesselcharacteristics. The growth processes of the stem segment throughwhich the vasculature extended were incorporated in these modelsto illustrate how a functional vascular system is maintainedin the stem as a whole. The central trace sympodia representedthe integrals of the temporal and spatial functions for individualcentral leaf traces. Metaxylem vessel production ceased in individualleaf traces two plastochrons before the cessation was reflectedin the central trace sympodia because of the integrative natureof the sympodial complex. A functional continuum of developmentwas apparent between metaxylem vessels of the central tracesympodia and secondary vessels of the stem. The transition betweenmetaxylem and secondary xylem production in the central tracesympodia corresponded with cessation of leaf and internode elongation. Populus deltoides Bartr. ex Marsh., cottonwood, primary xylem, secondary xylem, primary-secondary vascular transition, leaf growth, xylogenesis     

Relationships Between Climate and Flowering of Eight Herbs in a Swedish Deciduous Forest

Effects of annual variation in rainfall, temperature and humidityon flowering abundance of eight temperate woodland plants (Anemonenemorosa, Cardamine bulbifera, Lamiastrum galeobdolon,Oxalisacetosella , Ranunculus ficaria, Stellaria holostea, Viola reichenbachianaand Viola riviniana) were studied during 12 consecutive years(1989–2000) in a hornbeam (Carpinus betulus) forest insoutheast Sweden. Above-average rainfall/humidity in late summerto early autumn of the preceding year increased flowering abundancein L. galeobdolon, O. acetosella, V. reichenbachiana, V. rivinianaand, especially, in R. ficaria, but not in S. holostea and A.nemorosa. Moreover, flowering of R. ficaria and O. acetosellawas positively related to rainfall/humidity during several partsof, or the entire, preceding year. On the contrary, floweringof S. holostea and A. nemorosa was closely related to low valuesof rainfall/humidity in autumn and/or winter of the precedingyear and also to low humidity in the current year in A. nemorosa.Two long periods (3–4 years) of increasing rainfall deficitcoincided with decreasing flowering abundance in most of thespecies, but not with decreasing vegetative development. Temperaturevariability was less consistently related to flowering. A coolperiod during the preceding summer or autumn seemed importantfor flowering in L. galeobdolon, O. acetosella and the Violaspecies, although these relations were, at least partly, causedby interactions with rainfall/humidity. No significant (P <0.05) correlations were found between flowering and the conditionsprevailing in April to May—the main flowering season—ofthe current year. Copyright 2001 Annals of Botany Company Climate, flowering, rainfall, temperature, Anemone nemorosa, Cardamine bulbifera, Lamiastrum galeobdolon, Oxalis acetosella, Ranunculus ficaria, Stellaria holostea, Viola reichenbachiana, Viola riviniana     

Daphnia invasion: population dynamics of Daphnia assemblages in two eutrophic lakes with particular reference to the introduced alien Daphnia ambigua

The population dynamics of Daphnia species (D.cucullata, D.ambigua,D.galeata) in two small, productive lakes were studied and experimentswith field enclosures were carried out to elucidate the ecologicalniches of the introduced, alien species D.ambigua. Daphnia ambiguocoexisted temporally with the similarly sized D.cucullata, butlived in deeper water. Although both species had the same clutchsizes, similar proportions of ovigerous females, and death rates.D.cucullata was nurnerically dominant over D.ambigua. This suggeststhat the observed difference in abundance is simply a resultof the slower population growth rates of D.ambigua at lowertemperatures in greater depths. The experiments with field enclosuresshowed that when D.culcullata and D.ambigua were forced to livein the same layer of water, D.ambigua was numerically dominantover D.culullata both in the enclosures with and without fish.As the difference between the abundances of the two speciesdecreased in the enclosure with fish, D.cucullata seems to bebetter protected against fish predation than D.ambigua. In theenclosures without fish, D.ambigua and D.cucullata were numericallysurpassed by the larger species D.galeara. The present resultsimply that in some productive lakes with a high fish stock,D.mbigua invaded the niche of D.galeara and that the speciescan become an important component of the native zooplankton.The results also support the opinion that co-existing Daphniacan have very similar dynamics and niches. ¹ Present address: Zoologisches Institut, Christian-Albrechts-UniversitätKiel, Olshausenstrasse 40, D-24098 Kiel, FRG     

Morphological and mitochondrial-DNA analysis of the Indo-West Pacific rock oysters (Ostreidae: Saccostrea species)

Species of Saccostrea are common oysters on Indo-Pacific rockyshores. The taxonomy of this genus is unclear, however, becauseof morphological plasticity among its constituent species. Oystersamples with distinct morphotypes were collected from shoresexperiencing different degrees of wave exposure in Japan, Taiwan,China, Vietnam, Singapore and Australia. Intraspecific and interspecificvariations in shell characters have been identified. Only S.kegaki could be readily differentiated from S. cucullata-B,S. cucullata-C and S. mordax by multivariate shell allometricanalyses. Phylogenetic analyses using partial mitochondrial16S DNA sequences of approximately 513 base pairs identifiedtwo clades that correspond to superspecies, i.e. putative S.cucullata and putative S. mordax, comprising nine and two lineagesfrom the Indo-West Pacific, respectively. These are S. cucullata-A,B, C, D, E, F, G, S. kegaki and S. glomerata in one clade, andS. mordax-A and B in the other. Interspecific sequence divergence(Kimura-2-parameter values) between lineages ranged from 1.02%to 11.74%. Both S. cucullata-C and S. kegaki are restrictedto the northern hemisphere, whereas S. glomerata seems to bea temperate species from the southern hemisphere. S. cucullata-Doccurs only in Taiwan. Other species, i.e. S. cucullata-A, B,D, E and F and S. mordax-A and B, have a wide range on rockyshores in the tropical and subtropical Western Pacific and inboth northern and southern hemispheres. (Received 7 January 2005; accepted 4 November 2005)     

Instar-dependent mortality rates of coexisting Daphnia species in Lake Vechten, The Netherlands

In Lake Vechten, population parameters were determined for twocoexisting Daphnia species, D.hyalina and D.cucullata, fromApril 23 to December 10, 1986. Daphnia hyalina is dominant inspring and D.cucullata in summer and autumn. Size frequencydistributions were converted into instar frequency distributionsby using experimental growth curves and field measurements onnewborn size and the size at first reproduction. A discreteevent computer model was used to calculate the instar mortalityrates. Relative importances of instar mortality rates for thepopulation mortality rate were calculated and discussed. Themortality of the juvenile stages was found to be more importantthan adult mortality during most of the sampling season, despiteegg mortality when egg-bearing females are killed. Only in Septemberand October was the mortality of adult instars more important.Correlation coefficients between differences in the rates ofincrease and differences in mean brood size and instar mortalitiesshow that the former are caused mainly by differences in juvenilemortality, the main factor determining the replacement of D.hyalinaby D.cucullata during early summer.     

A Histopathological Study of Anomalous Growth in the Stem of Coccinia indica W. & A. Infested with Neolasioptera cephalandrae Mani

Gall formation due to attack of the larvae of Neolasiopteracephalandrae is common on the stem of Coccinia indica. Isolatedpatches of secondary meristematic centres develop throughoutthe proliferated tissue and they often differentiate into vasculartissues (either xylem or phloem or both). The larvae bore throughthe stem and live in lysigenous cavities in the ground tissue.Proliferation of cells of the secondary meristematic centresresults in gall formation and the normal vascular pattern isdisturbed and vascular bundles crushed. Development of mechanicaltissues in the affected region is suppressed. Additional cambiallayers with no definite pattern of orientation also developin the ground tissue and these produce patches of xylem tissue.Larval cavities are irregular and are surrounded by a nutritivetissue rich in protein and polysaccharides.     

Structure and Development of the Mature Secondary Haustorium in Alectra vogelii Benth

Anatomical investigations were carried out on the structureand development of the mature secondary haustorium in Alectravogelii growing on Arachis hypogaea or Vigna unguiculata. Followingthe formation of the young secondary haustorium, both the cambiumand pericycle of the host root directly opposite the young secondaryhaustorium are stimulated to divide and form new tissues andorgans including haustorial roots. Further proliferations ofthe host root pericycle and the haustorial cortex give riseto a large, tuberous and complex mature secondary haustoriumwithin which the tissues of the host and parasite remain inintimate contact forming a perfect graft union with a wide zoneof contact. Apart from the haustorial axial xylcm strand whichnormally connects the xylem of the parasite secondary root withthat of the host, direct xylary connections are also establishedbetween the axial xylem of the haustorium and the xylem of thehaustorial roots. The entire surface of the mature secondaryhaustorium of Alectrais covered with these haustorial rootsas was previously observed in its mature primary haustorium. Alectra vogelii Benth, secondary haustorium, haustorium, haustorial roots, root parasite, hemiparasitism, Arachis hypogaea, Vigna unguiculata     

Seed desiccation limits removal by ants

Ants collect and disperse seeds that bear an attractive nutritive body called the elaiosome. In mesic habitats, many myrmecochorous plant species have elaiosomes that are usually soft and desiccation-sensitive. The aim of this study was to link the desiccation rate of two species of seeds (Chelidonium majus and Viola odorata) to the seed-removing behaviour of the ant Myrmica rubra. In laboratory experiments seeds of both species lost one-third of their weight in 24 h. Concurrently, seed removal rates decreased sharply (92%) for Viola odorata over 24 h and slowly for Chelidonium majus, which retained one-third of its attractiveness after one month of desiccation. Seeds recovered their initial weight almost entirely after being soaked in water for 18 h. This rehydration partially (Viola odorata) or totally (Chelidonium majus) restored the attractiveness of the seeds. In this paper, we show that the window of seed attractiveness during which ant–plant interactions occur is desiccation-dependent and plant-specific.     

The Developmental Anatomy of the Root System in Yam Bean, Pachyrhizus erosus Urban

Investigations revealed that the anatomy of the primary radicularroot of yam bean (Pachyrhizus erosus L.) was typically dicotyledonousexcept that the xylem was not completely developed centripetally.Most of the roots had tetrarch xylem, although a few triarchand pentarch roots were also observed. In both tuberous andnon-tuberous roots, secondary thickening occurred by the formationof the meristematic vascular cambium which formed secondarytissues in a normal fashion. Subsequently, tuberization wasinitiated in the secondary xylem by the development of anomalous‘secondary’ cambia from parenchyma cells surroundingvessel elements. Anomalous ‘secondary’ cambia alsodeveloped from parenchyma cells not associated with vessels.Subsequently, anomalous ‘tertiary’ cambia differentiatedfrom tissues produced by the anomalous ‘secondary’cambia. Activities of these anomalous cambia resulted in theproduction of parenchyma storage cells and were chiefly responsiblefor the growth of the mature tuber. Pachyrhizus erosus L., yam bean, tuberous root, anatomy, anomalous ‘secondary’ cambia, anomalous ‘tertiary’ cambia, centripetal xylem development     

Regeneration Around Wounds and the Control of Vascular Differentiation

The question which was the basis of this work was whether (a)vascular regeneration around wounds includes a replacement ofdamaged tissues or (b) only new vascular strands, which arenormally formed from the cambium, are diverted around wounds.It was found that in Coleus and Cucumis no connections are formedto damaged sieve tubes and vessels, so that their continuityaround wounds is not restored. Pisum plants were wounded underconditions in which growth could not be influenced and the areaof the xylem in cross-section was measured 1 month later. Thewounds, which damaged the vascular tissues, significantly increasedvascular differentiation, indicating the replacement of a longnon-functional region of damaged tissues. The results indicatethat in the intact plant vascular differentiation is controllednot only by stimuli from the leaves but also by the capacityof the mature vascular system to transport these stimuli.     

Influence of Flooding on Net CO2Assimilation, Growth and Stem Anatomy of Annona Species

A series of experiments was conducted to assess net CO₂assimilationand growth responses to waterlogging of grafted and seedlingtrees in the genus Annona. Seedlings of A. glabra, A. muricataandA. squamosa L., and scions of ‘Gefner’ atemoya(A. squamosaxA. cherimola Mill.), ‘49-11’ (‘Gefner’atemoyaxA. reticulata L.), ‘4-5’ (‘Priestley’atemoyaxA. reticulata), A. reticulata grafted onto either A.glabra, A. reticulata orA. squamosa rootstocks were floodedfor up to 60 d. Soil anaerobiosis occurred on the third dayof flooding. Seedlings ofA. glabra and A. muricata, and thescions ‘49-11’, ‘Gefner’ atemoya, andA. reticulata grafted onto A. glabra rootstock were consideredflood tolerant based on their ability to survive and grow inflooded conditions. Scions of the normally flood-sensitive A.reticulata, ‘Gefner’ atemoya, and ‘49-11’tolerated root waterlogging when grafted onto the flood-tolerantspecies, A. glabra. In contrast, flooding of A. squamosa seedlingsand rootstocks, and A. reticulata rootstocks greatly reducedgrowth and net CO₂assimilation rates, and resulted in 20–80%tree mortality. Stem anatomical responses to long-term flooding(12 continuous months) were assessed in seedlings of A. glabraand A. muricata, and trees of ‘49-11’ grafted ontoA. glabra. Flooded trees developed hypertrophied stem lenticels,particularly in A. glabra, and enlarged xylem cells resultingin thicker stems with reduced xylem density. Flooding did notincrease air spaces in pre-existing xylem near the pith or inxylem tissue that was formed during flooding. Thus, flood tolerancedid not involve aerenchyma formation in the stem. Copyright1999 Annals of Botany Company Flood tolerance, net CO₂assimilation, photosynthesis, stem anatomy, shoot growth, anaerobiosis, Annonaceae.     

Effects of Growth Hormone Application on the Secondary Growth of Roots and Stems in Picea sitchensis (Bong.) Carr

Indol-3-ylacetic acid (IAA), gibberellin A3 (GA) and 6 benzylaminopurine(BAP) were applied factorially each at 3x10^–2 M in lanolinto the roots and stems of Sitka spruce seedlings and the activityof the two secondary meristems, the vascular cambium and phellogen,and of the parenchymatous tissues between them, was examined.All the treatments, with the exception of GA produced a localizedstimulation of radial growth at the point of application andthere was a similarity in the response of the various tissuesin both the root and stem. Radial growth of the xylem was notsignificantly affected in the roots whereas in the stems BAPand IAA stimulated growth. In the phloem BAP produced significantstimulation in both roots and stems and IAA stimulated growthin the roots. Growth of the parenchyma and periderm externalto the phloem was also strongly stimulated by both BAP, andIAA in roots and stems. In roots and stems the application of BAP altered the derivativesproduced by the vascular cambium, resulting in the productionof large multiseriate rays in the xylem, and giving rise toan overall increase in the proportion of ray tissue. Picea sitchensis (Bong.) Carr, Sitka spruce, secondary growth, xylem, phloem, periderm, wood rays, Indol-3-ylacetic acid, gibberellin A3, 6 benzylaminopurine, growth hormones     

Effects of seed aggregation on the removal rates of elaiosome-bearing Chelidonium majus and Viola odourata seeds carried by Formica polyctena ants

In a field dominated by Formica polyctena Foerst. ants, we examined the effect of seed aggregation on the seed-removal rates of two plant species: a large-seeded obligate myrmecochore Viola odorata L. and a small-seeded diplochore Chelidonium majus L., which was autochorous as well as myrmecochorous. The effect was statistically non-significant in V. odorata but significant in C. majus, with more closely aggregated seeds having higher removal rates. The large seeds of the obligate myrmecochore were more quickly discovered and repeatedly removed by ant workers than were the small seeds of the diplochore.     

Resource depression in Daphnia galeata, Daphnia cucullata and their interspecific hybrid: life history consequences

In this study, the effect of the food concentration on severallife history parameters of Daphnia galeata, Daphnia cucullataand the hybrid between these two species was examined. The foodconcentration had a significant effect on both growth and reproductionof all three taxa. Mortality was highly species specific, andto a lesser extent dependent on the food concentration. Changesin life history parameters resulted in changes in the intrinsicrate of population increase (r). The food dependence of thedifferent species was found to be different. Daphnia cucullatahad a relatively constant and low r. The r values for the hybridvaried most, with low values compared with the parental specieswhen grown at low food levels and relatively high values athigher food concentrations. Our results suggest that when foodconcentrations are high the hybrid will have a selective advantageover both parental species, but that at lower food levels D.galeatawill have an advantage over both D.cucullata and the hybrid.