Galium Aparine Research Articles

Alterations in phytosterol profiles of Galium aparine following treatment with BAS 480F

AbstractThe following are extended summaries based on posters presented at the 8th International Congress of Pesticide Chemistry (IUPAC), held in Washington, DC, USA 4–9 July 1994. They are entirely the responsibility of the authors, and do not necessarily reflect the views of the Editorial Board of Pesticide Science.

Abscisic Acid is a Causative Factor in the Mode of Action of the Auxinic Herbicide Quinmerac in Cleaver ( Galium aparine L.)

Summary Hydroponic treatment of cleaver plants (Galium aparine L.) with the quinolinecarboxylic acid herbicide quinmerac caused early symptoms, which were elicited within 48 h of quinmerac application (10-6 to 10-5 mol · L-1) and characterized by stem and leaf epinasty, retardation of root and particularly shoot growth, and reduction in water consumption. The levels of 1-aminocyclopropane-1-carboxylic acid (ACC), ethylene and conjugated ACC began to increase within 3 h and peaked at 24 h, 48 h, and 72 h of treatment, respectively. HCN was increasingly released from Galium shoots into the gas phase after 2 to 3 days of quinmerac application. The concentrations of gibberellins, cytokinins, and 3-indoleacetic acid (IAA) were only slightly changed. Within 24 h of treatment, the respective abscisic acid (ABA) levels in the shoot tissue were elevated up to 20-fold, relative to the control. Application of 10-4 mol · L-1 IAA increased ACC and ABA contents in Galium shoot and root tissues and induced phenotypic alterations in plants similar to those caused by quinmerac. Quinmerac-induced ABA accumulation was in close correlation with reductions in stomatal aperture, water consumption, photosynthetic CO2 uptake, and shoot and root fresh weights. Exogenously applied ABA mimicked quinmerac action on these parameters at comparable endogenous ABA concentrations. Additional treatment with the ACC synthesis inhibitor PACME decreased quinmerac-induced ACC formation, ABA accumulation, leaf epinasty and reduction of shoot growth. The effects of quinmerac could partly be restored when plants were additionally treated with ACC. This strongly suggests that ABA, induced ultimately through quinmerac-stimulated ACC synthesis, contributes to the auxinic mode of action underlying the inhibition of growth in cleaver.

The influence of fire onSpartina pectinatawetland communities in a northeastern Kansas tallgrass prairie

Wetlands dominated by the C4grass Spartina pectinata were investigated to quantify differences in plant species composition and diversity in response to fire frequency. The study site was a tallgrass prairie in northeastern Kansas that included Spartina wetlands subjected to spring fires at 1-, 2-, 4-, 10-, and 20-year intervals. Because C3forbs in these wetlands responded strongly to different fire frequencies, the light environment and gas exchange responses of the ubiquitous forb Asclepias syriaca were also assessed. In general, species diversity was lower in annually burned wetlands because of lower forb diversity. Maximum H′ in annually burned sites was 1.64 versus 2.77 in 10- and 20-year burned sites. However, individual forb responses varied. Asclepias increased and Solidago canadensis and Galium aparine decreased in importance with increasing fire frequency. Canopy sunlight interception was greater in annually burned wetlands than in wetlands with lower burn frequencies. Despite reduced light availability, midseason photosynthetic rates of Asclepias were higher in annually burned sites. The results suggest that frequent fire in tallgrass prairie wetlands results in less diverse plant communities, similar to responses of upland prairie, and that the timing of fire, relative to life history and phenology of the subordinate species, strongly influences responses of individual forbs. Key words: wetlands, tallgrass prairie, Spartina pectinata communities, fire.

Plant Species Migration in a Mixed‐History Forest Landscape in Eastern North America

The understory flora of successional forest in the Delaware/Pennsylvania Piedmont zone (USA) is species poor relative to old regrowth stands in the region. Impoverishment may reflect (a) limitations on dispersal of potential colonists, or (b) the unsuitability of successional stands for establishment. To examine the importance of dispersal, herb and shrub distributions were surveyed in successional stands of varying age and spatial arrangement. In successional stands contiguous with species—rich old—regrowth forest, understory species richness declined with distance into the successional stands, implying contagion across the old—regrowth ecotone. Individual species showed evidence of contagion in 67% of site x species combinations. Mean rates of migration ranged from to measurable movement (e.g., Carex laxiflora, Cimicifuga racemosa) to >2 m/yr in some species (e.g., Galium aparine, Potentilla canadensis). Significant differences in rate of migration were observed among seed dispersal modes: ingested > adhesive ° wind @> ants @> none. By contrast, there were no significant differences in rate between clonal and exclusively sexual species. In stands disjunct from old regrowth, the understory was species poor relative to old—regrowth forest due to a lack of species dispersed by ants and spores and those with no obvious dispersal vector. Understory species richness was greater in older disjunct stands and in stands closer to potential sources of propagules than in young and isolated stands, trends that were also noted in distributions of individual species. These results suggest that accessibility to colonists plays an important role in determining understory composition of successional stands. Medium— and long—range migration appears to be an issue of seed and spore dispersal rather than vegetative propagation. The extremely low migration rates of some species threaten their continued existence in the second—growth forest landscape.

Investigation into the Mechanism of Isoxaben Tolerance in Dicot Weeds

Isoxaben is an inhibitor of the synthesis of cellulose from glucose. Some dicot weed species are relatively insensitive to isoxaben inhibition. This study investigates mechanisms by which decreased sensitivity may occur in three dicot weed species: catchweed bedstraw, redroot pigweed, and velvetleaf. Dose response curves were generated to determine I50values for the inhibition of glucose incorporation into cellulose by isoxaben and compared to that of a sensitive species, mouse-ear cress. Metabolic detoxification and uptake rates were measured and the degree of tolerance conferred by these mechanisms was calculated. In all cases, metabolic detoxification was negligible. Lower uptake rates were significant but minor components of tolerance in all species. It is suggested that the principal cause of isoxaben tolerance in these dicot weed species is decreased sensitivity at the target site.

Automatische Erkennung von zehn Unkrautarten mit Hilfe digitaler Bildverarbeitung und Fouriertransformation

Abstract Automatic identification of 10 weed species in digital images using Fourier descriptors and shape parameters Plant species discrimination in mixed plant communities has recently become possible using transforms and shape parameters to classify digital images. In the present study image analysis techniques were used to identify weeds commonly found in winter cereal fields. Those species included Veronica hedenfolia L., Thlaspi arvense Beauv., Alopecurus myosuroides L., Apera spica‐venti L., Poa annua L., Stellaria media L., Capsella bursa‐pastoris L., Lamium purpureum L., Matricaria chamomilla L. and Galium aparine L. Images of several growth stages of these weeds were photographed using a Still Videokamera, binarified, the shape extracted and then Fourier descriptors and shape parameter were calculated for each weed. Classified digital images of each species were stored on the computer. A separate set of photographic images of these 10 weeds were used to test the ability of the classified images for plant identification.The average rate of correct identification was 81.9 % ranging from 41.6 % to 100 %.

Scale, Experimental Design and the Detection of Ineterspecific Competition within Plant Communities

Abstract We report preliminary results of a series of experiments designed to explore the importance of interspecific competition within arable weed communities at different scales. Competition hierarchies were apparent from a pot experiment with different levels of nutrients and water. Two field experiments looked at Bromus sterilis, Galium aparine and Papaver rhoeas in winter wheat in the field, in a range of combinations and management treatments, and a fourth field experiment included a wider variety of species. There was little effect of fertilizer on population behaviour in the the field. Bromus increased around ten fold per year on minimum‐tilled plots, regardless of other treatments. Galium increased on organically‐fertilized and minimum‐tilled plots, but only in the absence of Bromus. Papaver densities remained low, but again were depressed in the presence of high densities of Bromus. Taken together, the experiments demonstrate the existence of competition between weed species. However, as the design of the experiment increased to include greater levels of environmental variation, so competition became more difficult to detect, and less useful for interpreting the results than knowledge of the biology of the individual species. At the scale of interest to the farmer, the level of competition is not a good predictor for weed population dynamics.

Population Interactions and the Determinants of Population Size

Abstract The flux of individuals within populations is dependent upon six controlling processes: the intrinsic rate of increase of the plant, intraspecific competition for resources, interspecific competition, natural enemies, mutualisms and refuge effects such as the immigration of seeds from other populations. Although population interactions are generally believed to play a major role in determining the flux of individuals within populations, little attempt has been made to quantify the strength of these interactions and their role in the dynamics of populations. In this paper we examine the role of competition, herbivory and mutualistic interactions in determining the dynamics of a range of annual plant species. Firstly, it is shown that the dynamics of three weed species (Bromus sterilis, Galium aparine, Papaver rhoeas) in an experimental community in an arable cropping system of winter wheat are determined primarily by the rapid population growth of B. sterilis. Interactions between the species play a minor part in the dynamics of the system. Secondly, it is shown that current levels of grazing by overwintering populations of brent geese have a minor impact on the abundance of Salicornia europaea, but that increased grazing has the potential to reduce abundance and increase the instability of S. europaea populations. This is a consequence of the aggregative response of the geese, which results in an increasing proportion of the seeds of S. europaea being eaten as plant density increases. Thirdly, it is shown that there is a complex interaction between root pathogenic and arbuscular mycorrhizal fungi in natural field populations of Vulpia ciliata and that the benefit of mycorrhizal fungi to the plant is in providing protection against pathogens.

The effect of different frequencies of harrowing in the autumn or spring on winter wheat, and on the control of Stellaria media (L.) vill., Galium aparine L. and Brassica napus L.

Summary: Résumé: ZusammenfassungCultivating with a flexible tine harrow in the autumn reduced densities of Stellaria media (L) Vill., Galium aparine L. and Brassica napus L. plants and thinned the wheat crop. Effects were more severe with two passes at right angles (plant stands were approximately halved) than with a single cultivation. Despite crop thinning, wheat yields were not reduced by autumn harrowing owing to compensatory increases in 1000‐grain weights. Summer biomass of S. media and G. aparine was reduced more by spring than by autumn harrowing, while biomass of B. napus was only reduced by autumn harrowing. It was concluded that weakly rooted climbing or scrambling species are more easily controlled by cultivating in the spring, while species that develop a tap‐root are more readily controlled by cultivating at an early growth stage in the autumn. L'effet de différentes fréquences d'hersage en automne on au printempssur le blé d'hiver, etsur les controles suivants Stellaria media (L.) Vill., Galium aparine L. et Brassica napus L. Les façons culturales effectuées à 1'automne avec une herse à trilles flexibles réduisaient le nombre de Stellaria media (L.) Vill., Galium aparine L. et Brassica napus L. et éclaircissaient la culture de blé. Les effets étaient plus importantes après deux passages perpendiculaires (densité des plantes divisée par environ 2) que par un seul passage. En dépit de l'éclaircissement, les rende‐ments du blé n'ont pas été réduits par le hersage d'automne grâce à une compensation par le poids de 1000 grains. La biomasse d'été de S. media et G. aparineétait plus réduite par un hersage de printemps que d'automne, alors que la biomasse de B. napus n'était réduite que par un hersage d'automne. Les espéces grimpantes et faible‐ment enracinées sont done plus facilement com‐battues par des travaux de printemps, alors que celles qui présentent un racine pivotante sont plus facilement combattues par un hersage d'automne, à un stade précoce. Die Wirkung verschieden häufigen Eggens im Herbst oder im Frühjahr auf Wintenveizen und auf die Bekämpfung von Stellaria media (L.) Vill., Galium aparine L. und Brassica napus L. Eggen im Herbst mit einer beweglichen Zinkenegge verringerte die Dichte von Stellaria media (L.) Vill., Galium aparine L. und Brassica napus L. und reduzierte den Weizenbestand. Die Wirkungen waren durch 2 Arbeitsgänge im rechten Winkel zu einander, wobei der Pflanzenbestand ungefähr halbiert wurde, gegenüber einer einzelnen Bearbeitung ver‐stärkt. Aufgrund eines ausgleichenden Anstiegs des Tausendkorngewichts wurden die Weizenerträge trotz Ausdünnung der Bestände nicht durch Eggen im Herbst reduziert. Die Sommerbiomasse von S. media und G. aparine wurde mehr durch Eggen im Frühjahr als durch Eggen im Herbst verringert, während die Biomasse von B. napus nur durch Eggen im Herbst reduziert wurde. Daraus folgt, daß schwach wurzelnde und kletternde Arten einfacher durch Eggen im Frühjahr bekämpfbar sind, Arten mit einer Pfahlwurzel besser im Herbst zu einem früheren Entwicklungsstadium.

Influence à long terme du travail du sol sur la densité des levées d'adventices en situation de non désherbage

The sprouting of weeds was followed over a 9-year period (1977 – 1978 to 1985 – 1986) in a triennial rotation alternating between two spring cultures (barley–pea) and one winter culture (wheat) grown on two agricultural plots. The plots, one superficially worked while the other tilled, did not undergo any weeding treatment. A simultaneous increase in sprouting was observed in both plots at the beginning of the second rotation. However, this increase was greater on the superficially worked plot. The modifications within the adventitious community are qualitative in the first rotation, but become essentially quantitative at the beginning of the second rotation. Some species increase in density (Alopecurus myosuroides, Avena fatua, Galium aparine, Fallopia convolvulus, Sinapis arvensis, Thlaspi arvense) while others decrease (Amaranthus retroflexus, Kickxia spuria, Stellaria media). Key words: community, long term evolution, factorial analysis of correspondences, weeds. [Journal translation]

The Effects of Physical Support and Density on Biomass Production and Size Hierarchies of Galium aparine Populations

We assessed the growth and size inequality of experimental populations of Galium aparine at different densities with and without physical support. Those plants for which support was provided gained more weight than those unsupported. The presence of support increased the relative growth rate of the plants and reduced mortality at the highest densities. The biomass of the population was also higher in the case of supported plants. The size inequality of the population was not 'affected by the support-treatment but varied with density. Since density-dependent mortality took place at higher densities, and the variation of the relative growth rate increased with density, dominance-suppression could be assumed (...)

Weeds as hosts of Mycocentrospora acerina

SummaryWeeds were collected from carrot fields and some other sites at 27 localities in seven counties in Norway during August and September of 1986 and 1987. Leaf and petiole lesions were microscopically examined for Mycocentrospora acerina. Viola arvensis and Viola tricolor were commonly observed with the pathogen. The fungus was also registered on Fumaria officinalis, Galium aparine, Matricaria inodora, Matricaria matricarioides, Ranunculus repens, Senecio vulgaris and Stachys palustris. In inoculation experiments in the greenhouse, M. acerina infected carrot leaves and 13 of 16 species of weeds. The symptoms on the various susceptible plants showed some variation, but were essentially of the same pattern. The investigation indicates that weeds are common hosts of M. acerina. A list of 23 host weed species is given.

Modern Ecology: Basic and Applied Aspects.

Preface. Editorial advisors. List of contributors. I. MORPHOLOGY, STAND STRUCTURE, AND COMPETITION. 1. Morphology in modern ecological research (W. Eber). 2. Vegetation structure, phytomass and phenology of the dry thorn scrub of Curacao, West Indies (M.J.A. Werger, C. de Bok and B. Oranje). 3. Structure and phytomass production of a pioneer community (M. Jochimsen and D. Janzen). 4. Survival and growth beneath and near parents: The case of Myrcianthes fragrans (Myrtaceae) (D.F. Whigham and E. Cabrera Cano). 5. Colonizing success in plants: Genetic variation and phenotypic plasticity in life history traits in Capsella bursa-pastoris (H. Hurka and B. Neuffer). 6. Niches of longevity and stress (F. Klotzli). II. MASS AND WATER BALANCES AT STAND LEVEL 7. Plasticity of the photosynthetic production of Galium aparine L. (W.L. Kutsch and L. Kappen). 8. Diversity of photosynthetic responses in the mesic and arid Mediterranean-type climate regions of southern Africa (M.C. Rutherford). 9. The combination of measurements and mathematical modelling for assessing canopy structure effects (U. Tappeiner and A. Cernusca). 10. The water balance of deciduous forests: methods and models (B. Saugier and J.-Y. Pontailler). 11. Combination effects of water and salt stress on growth, hydration and pigment composition in wheat ( Triticum aestivum L. ): A mathematical modelling approach (K.H. Kreeb and T. Chen). 12. Ecosystem research on grassland in the Austrian Alps and in the Central Caucasus (A. Cernusca). III. MINERALS AND VEGETATION-SOIL INTERACTIONS 13. Multi-element analysis in plant material (B. Markert). 14. Significance of nutrient relations and symbiosis for the competitive interaction between grasses and legumes in tropical savannas (E. Medina and B. Bilbao). 15. Correlations between the microbial activity, and water, air, temperature and nutrient status of different soils under different land use (H.-P. Blume, L. Beyer and F. Friedrich). IV. DISTURBANCES AND MANAGEMENT OF SEMI-NATURAL AND AGRICULTURAL SYSTEMS 16. Fire, dry heat and germination of savanna grasses in Botswana (W.H.O. Ernst). 17. Does intermediate disturbance increase species richness within deciduous forest understory? (R.J. Reader, K.C. Taylor and D.W. Larson). 18. Response of a Bromus erectus grassland Mesobromion to abandonment and different cutting regimes (H. Dierschke and M. Engels). 19. Phytosociology of vineyards - results, problems, tasks (O. Wilmanns and A. Bogenrieder). 20. The dissipation of energy through soil invertebrates in wheat field and meadow (L. Ryszkowski). V. EUTROPHICATION AND POLLUTION IN TERRESTRIAL SYSTEMS 21. Lead tolerance of annuals at roadsides (U. Hellmuth and W. Schmidt). 22. Environmental mutagenesis: mutational load in natural populations of Eisenia fetida ? (W. Nau and W. Kohler). 23. The sublethal enchytraeid test system: guidelines and some results (W. Westheide and D. Bethke-Beilfuss). 24.

Phenology of arable and hedgerow populations of Galium aparine L. in relation to climate and soil conditions

Summary: Résumé: ZusammenfassungData collected in seven experiments in greenhouses or phytotrons were used to develop an empirical description of the phenology of populations of Galium aparine L. (cleavers). Cleavers from a hedgerow population were found to differ from cleavers from an arable population in their need for vernalization. Moisture regime and amount of light proved to be unimportant for the timing of flowering. Nutrition had some influence on the timing of flowering, but daylength and maximum temperature were most important in this respect. Both can be involved by summation of the product of daylength and the effective maximum temperature (°C above the base temperature of 5.3°C). The resulting descriptive formula enables relevant developmental rates of arable field populations to be predicted over a broad range of environmental conditions. The flowering date in the field of cleavers from an arable population could be correctly predicted for cohorts of plants emerging at different dates in two independent sets of data collected in England and The Netherlands, by using this summation (17300 °C* h between emergence and flowering). The temperature sum divided by 17300 can also be used as a developmental scale that governs the changes in patterns of carbohydrate partitioning. Although the development of the first whorls on cleavers is primarily related to the mean day temperature, the summation can also be used to describe the development of the first whorls. Phenologie des populations de Galium aparine L. de terres arables et des haies en relation avec les conditions pedoclimatiques Des donnees collectees dans 7 expérimentations en serre ou en phytotron ont été utilisée pour développer une description empirique de la phénologie des populations de Galium aparine L. (gaillet). Les gaillets issus d'une population de haie se sont révélés différents des gaillets issus d'une population de terre arable dans leur besoin de vernalisation. Le régime d'humidite et la quantité de lumière n'a pas d'importance pour repoque de floraison. La nutrition a quelque influence sur l'epoque de floraison, mais la longueur du jour et la temperature maximale sont plus importantes k cet egard. Les deux peuvent être impliquées par la sommation du produit de la longueur du jour avec la température maximale efficace (°C au‐dessus de la température basale de 5,3). La formule descriptive qui en éesulte permet de prévoir les taux de developpement des populations en champs labourés sous un large éventail de conditions environnementales. La date de floraison au champ des gaillets issus d'une population de terre arable a pu etre correctement prévu pour des vagues de plantes levées k des dates differentes à partir de deux lots de donnees independantes collectees en Angleterre et aux Pays‐Bas en utilisant cette sommation (17300°C* heure entre la levée et la floraison). La somme de température divisée par 17300 peut aussi être utilisée comme une échelle de développement qui règie les changements dans les schqui regie les changements dans les schemas de la partition carbohydrate. Bien que le développement des premières verticilles chez le gaillet soit principalement liéà la température moyenne joumalière, la sommation peut aussi etre utilisee pour decrire le développement des premiers verticilles Phänologie von Feld‐ und Heckenpopulationen von Galium aparine L. je nach Witterung und Bodeneigenschaften Mit Ergebnissen aus 7 Versuchen im Gewächshaus oder Phytotron wurde eine empirische Beschreibung der Phänologie von Galium aparine (Kletten‐Labkraut‐) Populationen entwickelt. Kletten‐Labkraut aus Heckenpopulationen unterschied sich von Feldpopulationen durch die Notwendigkeit der Vernalisation. Bodenfeuchtigkeit und Lichtin‐tensität erwiesen sich für den Blühbeginn als unwichtig. Düngung hatte einigen Einfluß auf den Blühbeginn, doch Tageslänge und Temperaturmaxima waren dafür sehr wichtig. Beide Faktoren können als Summe des Produkts der Tageslänge mit der effektiven Maximal‐Temperatur (°C über der Basistemp‐eratur von 5,3 °C) einbezogen werden. Die daraus resultierende beschreibende Formel er‐laubt es, rele van te Entwicklungsraten von Feld‐populationen über eine große Breite von Umweltbedingungen zu prognostizieren. Das Bluhdatum einer Feldpopulation von Kletten‐Labkraut konnte für zu verschiedenen Zeiten in 2 unabhängigen Sätzen keimende Pflanzen‐gruppen, die in England und den Niederlanden gesammelt worden waren, durch Anwendung dieser Summe (17300°C* Stunden zwischenKeimung und Blüte) korrekt vorhergesagt werden. Die Temperatursumme, geteilt durch 17300, kann auch als Entwicklungsskala genutzt werden, die die wechselnde Kohlen‐hydratspeicherung umfaßt. Obwohl beim Kletten‐Labkraut die Entwicklung des 1. Blatt‐quirls hauptsachlich von der mittleren Tages‐temperatur abhangt, kann dieses Stadium auch mit der Temperatursumme beschrieben werden.

The use of IR microspectroscopy in the analysis of etowah textiles: evidence of dye use and pseud0m0rph formation

Previously, our laboratory reported the analysis of archaeological textiles from the Paracas Necropolis (400 BC - 400 AD) in Peru. The study has been expanded to include textile fragments from the Etowah Mound C located in Northwest Georgia. These fragments have been dated approximately 1200 AD. Samples were removed from four textile fragments, catalog numbers EMC 640, EMC 842, EMO A842, and an unnumbered copper covered ear disk. These textiles have been described in detail in other publications. Infrared and visible spectra were obtained from fibers removed from each of these fragments, as well as spectra of three dye plant extracts (Galium corymbosium, Galium aparine, Rubia tinctoria or cordifolia) and spectra of alum mordanted wool dyed with those extracts.IR spectra are obtained on an Analect AQS-20M IR microspectrometer system with an MCT narrow band detector. Single fibers are prepared for analysis by flattening with a metal probe and transferring to a 1 mm-thick KC1 plate. Typical sample areas range from 30 to 50 μm in diameter.

A New Phytotoxic Activity of the Cyclic Peptides Tentoxin and Dihydrotentoxin

AbstractExtracts of culture filtrate of the phytopathogenic fungus Alternaria alternata (Fries) Keissler cause distinct wilting of cuts of the problem weed Galium aparine L. We were able to demonstrate that the cyclic tetrapeptides tentoxin and dihydrotentoxin were reponsible for this effect. A tentoxin derivative, isolated from the culture filtrate, shows a similar, but stronger wilting activity.

Architectural analysis of plant root systems

summaryThe techniques of architectural analysis were applied to the root systems of plants growing under field conditions, to determine their validity in this situation and to measure the extent and causes of plasticity and of interspecific differences in root architecture in co‐existing species. In a three‐year study of two species (Trifolium repens L. and Plantago lanceolata L.) on eleven different soils, large differences were found between species, soils and years; much of the variation in the root architecture of T. repens could be explained in terms of soil moisture concentration. On two woodland sites, the root architecture of five species was followed over a 15–month period, and at one a manipulative experiment involving irrigation and nitrogen and phosphorus addition was set up. There were large differences between species in root architecture and seasonal changes in some aspects (topology and exterior link length), which probably represent developmental patterns. Irrigation induced topological changes in one species (Galium aparine L.) which were consistent with the results of the three‐year study, but not apparently with an earlier model. In the case of Mercurialis perennis L., however, both irrigation and N and P addition brought about the predicted changes in root architecture, namely shorter interior links and lower topological index, though N had the opposite effect on exterior links. Interior link length differed widely between species, but showed little temporal variation, suggesting that it may be a valuable character for further studies. These results illustrate the validity and potential of architectural analysis for the study of root systems extracted from field soils.

The Effect of Local Shading and Darkening on Branch Growth, Development and Survival in Trifolium repens and Galium aparine

Various measures of growth and development together with 14 C-assimilate distribution patterns were used to investigate the response of shading or darkening of a single well established based branch in two contrasting species, Galium aparine and Trifolium repens. Shading a basal branch had similar effects in both species in that its production of axillary branches and biomass were reduced; G. aparine also showed reduced leaf whorl production. In G. aparine darkening an established basal branch resulted in its rapid death, but in T. repens stolon elongation continued as normal but axillary branching ceased. With the exception of the root system, neither shading nor darkening had any significant effect upon the growth and development of the rest of the plant (...)

Seedbank persistence and seedling emergence of seven weed species in autumn‐sown crops following a single year's seeding

SummarySeedbanks and seedling emergence, resulting from seeds shed in wheat crops and ploughed in, were monitored in two experiments for 3–4 years in successive autumn sown crops, in which herbicides were used to prevent re‐seeding. Populations of Galium aparine, Papaver rhoeas, Lamium purpureum, Myosotis arvensis, Veronica persica, Viola arvensis and Veronica hederifolia were studied in separate plots. The numbers of viable seeds in the soil declined exponentially; G. aparine and V. hederifolia declined most, and P. rhoeas and V. arvensis least rapidly. Total weeds (all species) over the 3–4 years, (obtained by adding successive numbers of seedlings recorded in each autumn or winter), represented 3–4% of the first year seedbank for the combined species. Few seedlings emerged in the first year after seeding due to effective burial by the initial ploughing. The species showing the greatest emergence in the first year, relative to seedbank size, were G. aparine and V. hederifolia. Other, smaller seeded, species produced their main seedling flushes in the second and third years after seeding. It is concluded that poor weed control in one year is likely to result in large weed infestations for up to four years and probably longer for some species.

Investigations on the Selectivity and the Metabolism of the Herbicide Bromoxynil in Plants

Summary The metabolism of 3,5-dibromo-4-hydroxybenzonitrile (bromoxynil) was studied in plants that show a very different susceptibility to the active ingredient. Depending on the susceptibility of the corresponding plant, a graduate rate of metabolism was found. In plants extensively resistant to bromoxynil (Stellaria media, Hordeum vulgare), a rapid metabolization was observed. In Chrysanthemum segetum and Lycopersicon esculentum, both species being moderately susceptible, significant parts of the parent compound remained unchanged. Galium aparine, a very susceptible plant species, was not able to metabolize significant amounts of bromoxynil.