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Summary • Although Scotch thistle (Onopordum acanthium) is known to have cypselas whose dormancy is affected by maturation temperature, a detailed study of plant development, cypsela structure and germination responses after maturing under contrasting temperatures has not been done. • Plants were grown under high and low temperature regimes in glasshouses and under field conditions in 2000 and 2001. Each year, phenological and developmental characteristics of plants were monitored and cypselas were collected twice. Cypselas were germinated fresh and after 4 months after-ripening, and also examined for surface and internal characteristics by scanning electron microscopy. • Plants from the lower temperature regime were taller, had thicker shoots, larger leaves, larger capitula that appeared sooner, and more, slower-to-mature and larger cypselas with smoother surfaces, thicker coats and higher moisture contents. However, their germination percentages were lower. After after-ripening most cypselas germinated. • In both years, consistent and significant differences in germination patterns and structural characteristics between cypselas from the two temperature regimes indicated that both pre- and postdispersal factors were involved in regulating the germinability of O. acanthium cypselas.

Proso millet, Panicum miliaceum L. (Poaceae), has been a crop in Asia and Europe for 10 000 years and for over 300 years in Canada, where it is grown for grain, rescue crops, birdseed, forage, and ...

In the mid-1960s the founding of the Canadian Botanical Association provided a forum for the discussion of new botanical initiatives in Canada. At that time there was, coincidentally, a much increased interest in several areas of botany that had previously been little studied or ignored (e.g., plant autecology, plant population biology). As a result, many research projects became focused on individual species or small groups of closely related species. Botanists studying the native flora as well as those working with weed species became aware of the need for the compilation of all available information on important species, essentially in the format pioneered in Great Britain in the ‘‘Biological Flora of the British Isles’’. Botanists from the Central Experimental Farm in Ottawa (the Plant Research Institute) and the Botany Department at the University of Western Ontario in London decided to prepare a manuscript format for a Canadian version of the Biological Flora. Gerald Mulligan and Paul Cavers agreed to undertake this work. The initial plan was to ask the Editorial Board of the Canadian Journal of Botany to initiate a series with a tentative title ‘‘The Biological Flora of Canada’’. However, the Editor of the Canadian Journal of Botany did not accept this proposal. When we re-examined all the letters and other material received while the original proposal was being prepared, it was evident that by far the greatest support had come from scientists studying weeds and invasive plant species. In particular, many members of the Canada Weed Committee (later known as the Expert Committee on Weeds and currently as the Canadian Weed Science Society) enthusiastically recommended that this series be established. The Agricultural Institute of Canada, publishers of the Canadian Journal of Plant Science, agreed to publish the series under the title ‘‘The Biology of Canadian Weeds’’. We quickly revised the manuscript format to include aspects of weed biology not featured in the original proposal and published it in July 1972 (Cavers, P. B. and Mulligan, G. A. 1972. A new series The Biology of Canadian Weeds. Canadian Journal of Plant Science 52: 651 654). Gerry Mulligan was the first Editor of the series and Paul Cavers took the lead in finding authors and maintaining a list of Accounts in Preparation. The first account, published in October 1973, dealt with sheep-laurel (Kalmia angustifolia L.), a native species that is a weed of lowbush blueberry fields and pastures in eastern Canada. Since then, more than 150 accounts have been published, many on two or more species. In recent years, updates of several of the early accounts have been published. These updated accounts incorporate information on well-studied species published after the original account appeared. The series was popular from the outset, in fact there was such a great demand for many articles that the authors’ stocks of reprints soon were exhausted. In 1979, a book containing the first 32 accounts in the series was published by Agriculture Canada. Gerald Mulligan was the Editor and Compiler. In 1984, a second volume containing the next 29 accounts, with the same Editor/ Compiler and publisher, was printed. Volumes 3, 4 and 5 were published with Paul Cavers as the Editor/ Compiler by the Agricultural Institute of Canada in 1995, 2000 and 2005. In total, 129 original accounts plus three updated accounts were published in these five volumes (Table 1). In 2003, a new complimentary series was started, ‘‘The Biology of Invasive Alien Plants in Canada’’, in response to an expanding need for information on plants newly established or showing increased expansion in Canada, but for which there may be relatively little information available in a Canadian context. This series was intended to be similar in style and scope, but to concentrate on non-native plant species that have been more recently introduced into Canada than many of our common agricultural weeds, and for which there is substantial evidence that they may generate adverse economic impacts and management difficulties in agricultural systems or a broader landscape. The format for the Biology of Canadian Weeds has changed little over the years. Each contribution consists of 13 sections. The first section lists the currently accepted scientific name and the English and French vernacular names plus any synonyms that appear in the weed literature. The second section begins with a brief

Earlier studies have shown that seed germinability decreases with the physiological age of plants during seed development, but the effects of plant physiological age on the chemical constituents of fresh and after-ripened seeds and the relationship between chemicals and germination of such seeds have not been investigated fully. We studied this phenomenon in Scotch thistle ( Onopordum acanthium L.) cypselas. Mature cypselas were collected twice (early and late) from the same mother plants, which were grown under the temperature regime of 25/10 °C (14 h light, 10 h dark) in a walk-in growth chamber in 2000 and 2001. Cypselas were used fresh and after 4 months of dry storage at room temperature (∼25 °C, ∼37% relative humidity). Germination percentage, coefficient of germination rate, moisture content, wax load, lignin content, and phenolic compounds were determined for cypselas from all treatments. Germination percentages were higher for early-matured than for late-matured cypselas, and higher for after-ripened cypselas than for fresh ones. Late-matured fresh cypselas had greater moisture content than the early-matured fresh cypselas. After-ripening decreased cypsela moisture content and wax load. Plant physiological age and after-ripening did not affect lignin content. Overall, after-ripened cypselas had more phenolic compounds than fresh cypselas. Plant physiological age and after-ripening affect the chemical constituents of O. acanthium cypselas and their germination patterns.

Cavers, P. B., Qaderi, M. M., Threadgill, P. F. and Steel, M. G. 2011. The Biology of Canadian Weeds. 147. Onopordum acanthium L. Can. J. Plant Sci. 91: 739–758. In Canada, Scotch thistle, Onopordum acanthium L. (Asteraceae) is primarily a weed of well-drained natural areas and ruderal habitats such as abandoned gravel pits. It is classed as a noxious weed in Ontario and the North Okanagan region of British Columbia but is common only in southern Ontario. Native to southern Europe and southwestern Asia, it has been introduced to almost 50 countries in all continents except Antarctica. In parts of the United States it is a strongly competitive species that infests small grain fields and competes with desirable forage species in rangelands. It does have desirable attributes and has many uses including being consumed as a vegetable, used as a source of honey, yielding a burnable oil, incorporated in medications for many human ailments, providing grazing for goats, sheep and cattle and being grown as a garden ornamental. Despite its limited range in Canada, several distinct biotypes, differing in morphology, phenology and important ecological attributes, such as dormancy and longevity of cypselas (fruits) in the soil, have been described from southern Ontario. In Australia, a fertile hybrid of O. acanthium and O. illyricum is a major weed and there are concerns that these two species could be progenitors of a similar hybrid in North America.

European buckthorn, Rhamnus cathartica L., is an introduced shrub or small tree of forests, thickets, open pastures, hedgerows, roadsides, and riparian habitats. In Canada, it is found from Alberta east to the Maritimes, but is absent from Newfoundland. It is particularly abundant in southern Ontario. Problems arise from its status as an alternate host for the fungi Puccinia coronata Corda. f. sp. avenae Eriks., which causes crown rust and leaf rust of oats and for Puccinia coronata var. hordei Jin & Steff., which causes crown rust of barley. It is also the overwintering host for the recently invasive soybean aphid, Aphis glycines Matsumura, which has been described as a serious threat to soybean production in North America. Prolific fruit production, in combination with extensive seedling establishment and shade tolerance, allows R. cathartica to dominate an understorey quickly. Its ability to tolerate a wide range of conditions, at least in fairly moist areas, may lead to further expansion of its Canadian range. Control strategies should focus on reducing populations in close proximity to oats, soybeans or barley and to reduce its abundance in areas of ecological importance. Key words: Rhamnus cathartica, European buckthorn, Puccinia coronata, soybean aphid, weed biology

Investigations on seeds of Scrophularia marilandica L. were undertaken to determine their germination requirements. Seeds were collected from three naturally occurring sites and one greenhouse-grown population in London, Ontario in September and October of 1997. Some were set to germinate immediately after collection; others were stored in or on soil outside and/or under controlled laboratory conditions before testing. Germination was assessed under two light/temperature regimes (35°C 14 h light, 20°C 10 h dark and 25°C 14 h light, 10°C 10 h dark), in continuous darkness, and in the presence of two germination-promoting chemicals (GA3 and KNO3). Fresh seeds germinated best at 35/20°C, while stored seeds germinated best at 25/10°C. No differences in percent germination were found among three seed-maturity stages. All chemical treatments, except 0.01 M KNO3, increased percent germination. Significant differences were found both among and within sites for most chemical treatments, but exposure to 3 × 10−4 M GA3 caused almost every seed to germinate. When compared to the control, both the gibberellic acid and the soil-storage treatments contributed to faster germination. Exposure of seeds to naturally prevailing conditions on the soil surface followed by testing under the 25/10°C regime produced the highest percent germination. No seeds germinated in the dark. In summary, seeds of S. marilandica exhibit physiological dormancy, which can be alleviated by exposure to light, after-ripening and/or cold stratification. It is probable that the differences in germination response among sites can be attributed to differences in environmental conditions during seed production. These experiments indicate that the seeds of S. marilandica must be buried shortly after dispersal in order to form a persistent seed bank.

Altered collagen and elastin content correlates closely with remodeling of the arterial wall after injury. Optical analytical approaches have been shown to detect qualitative changes in plaque composition, but the capacity for detection of quantitative changes in arterial collagen and elastin content in vivo is not known. We have assessed fluorescence spectroscopy for detection of quantitative changes in arterial composition in situ, in rabbit models of angioplasty and stent implant. Fluorescence emission intensity (FEI) recorded at sites remote from the primary implant site was correlated with immunohistochemical (IH) analysis and extracted elastin and collagen. FEI was significantly decreased (P0.05) after treatment with anti-inflammatory agents, and plaque area decreased on comparison with saline-treated rabbits after stent implant or angioplasty (Por=0.013). Excellent correlations for FEI with elastin and collagen I, III and IV content measured by IH (R2or=0.961) analysis were detected by multiple regression (MR) analysis. Good correlations also were found for FEI with elastin and collagen measured by high-performance liquid chromatography; MR analysis provided highly predictive values for collagen and elastin (R2or=0.994). Fluorescence spectroscopic analysis detects quantitative compositional changes in arterial connective tissue in vivo, demonstrating changes at sites remote from primary angioplasty and stent implant sites.

Summary The regenerative responses of rhizomes and tubers from two populations of Helianthus tuberosus L. to burial and fragmentation were studied in field experiments. The regeneration of both populations varied with planting depth and stage of growth at which fragmentation occurred. Shoots of both populations emerged from rhizomes or tubers planted to depths of 30 cm. The percentage of tubers that regenerated was higher than that of rhizomes, particularly from deeper planting depths. The regeneration from rhizomes and tubers of a riverbank population was greater than that of a‘weedy’population. Rhizomes and tubers from both populations that had failed to produce shoots I year after planting were found to have decomposed completely. The significance of these results in relation to the distribution and control of H. tuberosus is discussed. Resume La capacite de regeneration des rhizomes et tubercules de deux populations d Helianlhus tuberosus L. (artichaut de Jerusalem) La capacite de regeneration des rhizomes et des tubercules de deux populations d'Helianthus tuberosus L. apres enfouissement et segmentation a eteetudiee dans une experimentation de plein champ. La regeneration des deux populations varie avec la profondeur d'enfouissement et le stade de croissance auquel la fragmentation est faite. Des pieds apparaissent a partir des rhizomes et des bulbes, chez les deux populations a des profondeurs d'enfouissement jusqu'a 30 em. Le pourcentage des tubercules regeneres etait plus grand que ce des rhizomes, surtout des profondeurs plus elevees. La regeneration des rhizomes et des tubercules d'une population de bord de riviere a ete plus elevee que celle d'une population‘herbeuse'. Les rhizomes et les tubercules issus des deux populations qui ne sont pas repartis un an apres la plantation, se sont averes etre completement decomposes. La signification de ces resultats en relation avec la repartition et la destruction de H. tuberosus est discutee. Zusammenfassung Die Regenerationskraft der Rhizome und Knollen bei zwei Populationen von Helianthus tuberosus L. (Topinambur) An zwei Populationen von Helianthus tuberosus wurde die Wirkung von Pflanztiefe und Teilung zu verschiedenen Entwicklungsstadien der Rhizome und Knollen im Freiland untersucht. Die Uberdauerungsorgane trieben noch bis zu einer Pflanztiefe von 30 cm aus. Knollen hatten eine hohere Austriebsrate als Rhizome, besonders bei grosserer Pflanztiefe. Die Regeneration war bei einer Population von einem Flussufer grosser als bei einer Unkrautpopulation. Nichtaustreibende Rhizome und Knollen waren nach einem Jahr vollig zerfallen. Die Bedeutung der Untersuchungsergebnisse fur die Verbreitung und die Bekampfung von Helianthus tuberosus wurde diskutiert.

The effects of maturation temperature on germinability and chemical constituents of Scotch thistle ( Onopordum acanthium L.) cypselas (fruits) were determined as part of our ongoing investigation into the causes of intermittent germination in this species. Mature cypselas were collected from plants that were grown under higher (28 or 30 °C) and lower (20 or 22 °C) temperature regimes in greenhouses in 2000 and 2001. Two collections were made, from early- and late-ripening capitula. Germinability and the amounts of moisture, wax, phenolic compounds, and lignin were determined for cypselas from all collections. Cypselas that matured in the first year had lower amounts of moisture and wax than second-year cypselas, but did not differ in amounts of other components. Cypselas that matured under the higher temperatures generally had lower amounts of moisture, wax, and phenolic compounds, faster germination, and higher germination percentages. Early-matured cypselas had higher amounts of moisture and wax, faster germination, and higher germination percentages, but lower amounts of phenolic compounds. However, maturation temperature and collection date did not affect lignin content. Consistent and significant differences in germination patterns and chemical constituents between cypselas that matured under contrasting temperatures confirmed that maturation temperature altered the germinability of O. acanthium cypselas. Thus, under field conditions, cypselas that mature under low temperatures can have stronger dormancy and exhibit greater intermittency in germination/emergence patterns than those that mature under high temperatures.

Field studies were conducted over 3 yr at two locations to evaluate the effects of glyphosate rate and application timing on barnyardgrass control, seed production, seed viability, and seedbank density the year after herbicide application in glyphosate-resistant corn. Glyphosate was applied at 0, 112, 225, 450, 675, or 900 g ai/ha when barnyardgrass was at the two-, four-, or six-leaf stage of growth. Visual estimates of percent control increased whereas density, dry weight, seed production, and seedbank density the year after treatment decreased as the rate of glyphosate was increased from 0 to 450 g/ha. Increasing the rate of glyphosate from 450 to 900 g/ha (registered rate) had no further effect on any measured parameter. Seed viability was not affected by glyphosate rate nor application timing. Corn yield declined only at a glyphosate rate of 225 g/ha and below. Barnyardgrass control improved as application was delayed to the six-leaf stage because this weed had an extended period of emergence. There ...

Field studies were conducted over 3 yr at two locations to evaluate the effect of glyphosate rate and time of application on common lambsquarters control, density, dry weight, seed production, and the number of seedlings emerging from soil cores taken the year after herbicide application in glyphosate-resistant corn. Glyphosate was applied at 0, 112, 225, 450, 675, or 900 g ai/ha when common lambsquarters were at the two-, four-, or six-leaf stage of growth. Nicosulfuron was applied to all experimental areas to control annual grasses. Visual estimates of percent control increased, whereas density, dry weight, seed production, and seedlings emerging the year after treatment decreased as the rate of glyphosate was increased from 0 to 450 g/ha. Increasing the glyphosate rate above 450 g/ha had little effect on these parameters. Corn yield declined only at glyphosate rates below 450 g/ha. Time of application had no effect on common lambsquarters control and corn yield because little emergence occurred after the first glyphosate application. There was no interaction between glyphosate rate and time of application for any of the parameters evaluated. In these studies, the application of glyphosate at half the manufacturer's registered rate provided control of common lambsquarters equivalent to the full-registered rate with no measured increase in weed seed production and no increase in weed seedlings emerging from soil cores the year after herbicide application. The results suggest that in some cases the use of reduced herbicide rates can provide excellent weed control and maintain crop yields, while reducing the cost of production and the environmental impact of herbicides. The use of extremely low rates (112 or 225 g/ha), however, resulted in reduced corn yields, increased common lambsquarters seed production and seedlings emerging the year after application, and possibly increased weed management costs in subsequent years.

Panicum capillare L., witch grass, is an annual grass native to North America that infests field crops, small grains, grasslands, and a variety of other habitats. High seed production, a persistent seed bank, a tumble-weed seed-dispersing mechanism, and the ability to tolerate some herbicides contribute to the success of P. capillare in these habitats. Despite the widespread presence of P. capillare in crops, its actual impact on crop yield is not well documented. It is an additional host for several insect pests (e.g., cereal aphids) and diseases attacking crop species. Key words: Panicum capillare, witch grass, panic capillaire, weed biology, native weed species

Three years ago, we published a revised format for the series on the Biology of Canadian Weeds, as well as instructions for the preparation of Updates of Previous Accounts (Cavers and Warwick 2000). This led to renewed interest in the series with 15 new accounts and two updates being published from April 2000 to October 2003. In addition, four new accounts and two updates have been accepted for publication, pending revision. There have also been many changes in the list of manuscripts in preparation. Since there are also a number of changes that need to be made in the Format and the Instructions to Authors, we are reprinting all of this information here. The term “weed”, as used in this series, refers to any vascular plant that perpetuates itself in habitats where it is not wanted. Individual contributions should contain accounts of a single weed species or a group of related species. Prospective authors should note that a new series, the Biology of Invasive Alien Plants in Canada, is being launched in this journal issue (Warwick et al. 2003). Before submitting an offer of contribution, authors should consider carefully the status and history of their species in Canada and then select the appropriate series. The Biology of Canadian Weeds series addresses undeniable problematic weeds in Canada, whereas the new series is designed to cover aliens in Canada that have demonstratable potential risk. In cases where the assignment to a particular series is not clear, the editors of both series may be called upon to make a judgment call. Please consult the new series (Warwick et al. 2003) for further information. If you wish to write an account on a weed species, you must first check to ensure that the species has not been assigned to someone else. This involves sending an “offer of contribution” to Dr P. Cavers. After approval of your offer, you may proceed with writing the paper. The completed paper is to be submitted directly to the Canadian Journal of Plant Science (see below). Offers of contributions by individuals or groups should be made to Dr. Paul B. Cavers, Department of Biology, University of Western Ontario, London, Ontario, N6A 5B7, e-mail pcavers@uwo.ca. These offers of contributions will be subject to approval by a committee of the Canadian Weed Science Society (CWSS). Approved offers will be subject to re-approval after three years if the article has not been completed during that period. Any inquiries about the format to be used or advice on preliminary drafts should be directed to Dr. Cavers. He can also supply blank maps of Canada and will suggest specialists or institutions that will provide various types of services for authors. The Canadian Weed Science Society has a web site [http://cwss-scm.ca/] with on-line references to common English and French names, links to provincial and federal legislation and current lists of species published and in preparation for this series. The finished manuscript should be submitted to: Canadian Journal of Plant Science; Mr. T. Fenton, Head, Journals Section, Agricultural Institute of Canada, 141 Laurier Ave. W., Suite 1112, Ottawa, Ontario, Canada K1P 5J3. All contributions must comply with the format of this journal. Accounts on a single species, including all maps, drawings, diagrams and photographs, should not exceed 50 pages [12 point font, double-spaced with numbered lines]. Of course, accounts on more than one species can be longer. The authors should also provide the names and addresses [including phone numbers and e-mails if available] of three potential referees.

Cypselas (fruits) of four local populations of Scotch thistle, Onopordum acanthium L., were stored for 3 months, heated gradually from room temperature to 50, 75, or 100°C and then gradually cooled to determine effects on germination. Populations responded similarly to this treatment. The lowest germination percentages and slowest rates followed the 100°C treatment, while the fastest germination rates followed 75°C. In a direct-heating experiment, cypselas (from central and peripheral positions in the capitulum) of one population were stored for 41/2 months and then exposed directly to 50, 75, or 100°C for 0.5, 1, or 2 min. This treatment at 75 and 100°C increased germination percentages, with higher percentages for the central cypselas. The 2 min treatment at 100°C yielded the highest percentage and fastest germination rate. Central cypselas were heavier but were similar to peripheral ones in imbibition and in the ratio between cypsela coat and embryo weights. In subsidiary experiments, wax-removed cypselas had smoother surfaces, heated cypselas had visible surface cracks, and germinated cypselas had thinner pericarps. Increases in the percentage and rate of germination in response to dry heat suggest that seedlings of O. acanthium may emerge sooner and in greater numbers following a fire event on disturbed or agricultural lands.Key words: cypsela, dry heat, germination, Onopordum acanthium, Scotch thistle, viability.

Cypsela dormancy in Scotch thistle (Onopordum acanthium) may be affected by the presence of chemical inhibitors. To investigate this phenomenon, a leachate from O. acanthium cypselas was tested for its ability to inhibit germination of the cypselas from which it was derived (i.e., autoinhibition). Leachates varied in their degree of autoinhibition, depending on the cypsela population from which they were prepared. Overall, removal of leachate from a group of O. acanthium cypselas increased their germinability. Using lettuce (Lactuca sativa) cypselas as an indicator species, bioactivity-guided fractionation was used to isolate a water-soluble, para-substituted benzamide from O. acanthium cypselas, which caused germination inhibition. Various chromatographic, spectroscopic, and spectrometric techniques were applied to the characterization of the bioactive compound.

Summary 1 Cypselas (fruits) of Scotch thistle (Onopordum acanthium) germinate unpredictably over a long period of time. We evaluated the effects of soil type, burial depth and collection date on the emergence patterns of two populations of O. acanthium, ESW and Quarry (Q). 2 From each of four separate collections made throughout 1996, five replicates of 200 cypselas each were placed on the surface or buried at depths of 3 or 15 cm in both sand and silt-loam soils (i.e. field conditions) and emergence was recorded biweekly between August 1996 and September 1999. 3 Emergence was intermittent over the 3 years, with a higher total percentage from silt loam (17%) than from sand (9%), and from 3 cm depth (18%) compared with the surface (8%). 4 After 3 years, all remaining viable, split (germinated but not emerged), decayed and unfilled cypselas were retrieved. Total germination over the 3 years (emerged plus split) was up to 77% at 3 cm in silt loam but always less than 10% at 15 cm in both soils for both populations. Although a higher percentage of cypselas germinated under controlled conditions when retrieved from loam compared with sand (89% vs. 66%), a significant number from all treatments did not germinate until scarified. 5 Cypselas that ripened under the warmest temperature (collection 3) had the highest emergence in the year of collection (1996), while more of those that ripened under cooler temperatures (collections 1 and 4) emerged in later years (1998 and 1999). Both initial and later emergence patterns for both populations varied greatly with collection date. This may be the first time that seedling emergence from the seed bank for different collections has been monitored over several years. 6 We compared waxes, lignins and soluble phenolics in the coats of cypselas retrieved from soil (early germinators) with those that germinated only after scarification. More surface wax was found in dormant cypselas. 7 Understanding these complex germination/emergence patterns may help develop control policies for O. acanthium.

Germination patterns were studied among three populations of Scotchthistle, Onopordum acanthium L. (Asteraceae). Cypselas(seeds) were collected twice during the growing season for four consecutiveyears (1996–1999) from plants grown in the same location, theEnvironmental Sciences Western Field Station (ESW) near London, Ontario.Cypselas from 1996 came from plants that had been transplanted as rosettes fromtheir original sites to ESW, while those for 1997–1999 came from plantsgrown from cypselas collected in 1996. Fresh cypselas were put to germinate at25 °C, 14 hlight/10 °C, 10 h dark for 55 days.Consistent and significant differences in final germination percentages amongpopulations were obtained over the four years. There were also differencesbetween collections within populations in 1996 and 1998. In addition, the finalgermination percentage (collectively) differed widely among years. There was agreater than 30 percent correlation between germination percentage and meandaily maximum temperature during cypsela maturation. Since there were similardifferences among populations every year, it appears that germination patternsof O. acanthium populations have a genetic basis as wellasan environmental one.

Echium vulgare L., known as blueweed or viper’s bugloss, is a blue or purple flowered biennial or short-lived monocarpic perennial herb found in every province in Canada. A naturalized weed of European origin, E . vulgare grows in highly disturbed are as, typically in soils of limestone or dolomite parent material. It is not competitive with crops, but serves as an alternate host for fungal pathogens and contains hepatotoxic alkaloids detrimental to livestock when consumed in large amounts. E. vulgare is a noxious weed in Nova Scotia, Québec, Manitoba, Alberta and parts of British Columbia. Beneficial aspects include contributions to honey production and herbal medicine. Key words: Echium vulgare, blueweed, viper's bugloss, weed biology

Leaf litter can affect seed germination and seedling emergence by altering both the physical and chemical environment. A series of experiments were conducted to investigate litter effects on germination and emergence of Cirsium vulgare seeds and seedlings. Thin (2 layers) and thick (5 layers) of leaf litter of Acer saccharum, Quercus alba, and Juglans nigra reduced and delayed seedling emergence of bull thistle (C. vulgare) in two greenhouse experiments. Leaves of J. nigra were less effective than those of the other two species. In one experiment, removal of the litter after seedling emergence had ceased was followed by a second flush of emergence, but no further emergence occurred in the non-litter control. However, in a second experiment no further emergence was recorded after litter removal. Artificial litter, chemical-free cotton paper cut in leaf shapes, reduced and delayed seedling emergence but to a lesser extent than natural leaf litter. Germination in distilled water in Petri dishes was n...

Seeds of bull thistle, Cirsium vulgare (Savi) Ten., were exposed to varying numbers of cycles of wetting and drying, in both Petri dishes and pots of soil, to investigate the effects of exposure to such cycles on subsequent germination of the seeds or emergence of the seedlings. Following exposure to the cycles, seeds in Petri dishes were set to germinate in one of four diurnal environments: 20:10°C alternating light and darkness, 20:10°C constant darkness, 30:15°C alternating light and darkness, or 30:15°C constant darkness. Total percent germination was reduced after exposure to eight cycles of wetting and drying, and germination rate was reduced after exposure to two or more cycles. Percent germination was reduced at the higher temperature but light availability had little effect. Reduction in seedling emergence in pots of soil after exposure to an intermediate number of cycles was greater than in Petri dishes but not as great with exposure to eight cycles. Seedling emergence patterns in pots that experienced any wetting-drying treatment were bimodal, with a second pulse of emergence several weeks after the termination of the cycles. This suggests that some seeds were induced into a dormant state through exposure to the cycles of wetting and drying. Such induced dormancy may serve to prevent seed germination in the autumn, promoting an attenuated and intermittent pattern of germination.Key words: Cirsium vulgare, bull thistle, wetting and drying, seed germination, induced dormancy, intermittent germination.

The effects of GA3, KNO3, and NaHCO3 on germination percentages and rates were determined for cypselas (seeds) of four local populations of Scotch thistle, Onopordum acanthium L., collected during a 2-year period. Three (1996, stored cypselas) and four (1997, fresh cypselas) concentrations (0.025, 0.05, and 0.1% for both years, plus 0.0125% for 1997) of the three compounds were used. Both freshly collected cypselas and those stored for 67 days at room temperature exhibited a range of germination responses from readily germinable to strongly dormant. GA3, even at a very low concentration, caused most viable cypselas to germinate, but 5-6% of viable cypselas in two populations did not respond to any GA3 treatment. In general, dry-stored cypselas germinated faster than fresh ones. Populations with more germinability (= proportion of cypselas capable of germinating) responded faster to GA3 than those with less germinability. KNO3 usually increased germination percentages but reduced the rate of germination. When treated with KNO3, stored cypselas from the two populations with less germinability germinated more slowly than those of the other two. In general, germination percentage decreased with an increase in NaHCO3 concentration. Overall, stored cypselas that were treated with NaHCO3 germinated more slowly than those in the control. The large differences among four local populations in response to these chemicals suggest that the effects of germination stimulators and other chemicals should be observed on several populations per species.Key words: cypsela, germination promoters, germination inhibitors, local populations, Onopordum acanthium, Scotch thistle.

Over the past 27 years the Canadian Journal of Plant Science has been publishing accounts on the biology of plants that are weedy in Canada. The series resulted from a recommendation by the Canada Weed Committee, now known as the Expert Committee on Weeds. The purpose was to bring together published and unpublished information on the biology of Canadian weeds, which could be utilized as a basis for effective economical and safe weed control methods and meet the needs of regulatory agencies in Canada. It was also intended that the series would result in research that would fill important gaps in our knowledge of the biology of these weeds. An article by Cavers and Mulligan entitled “A New Series – The Biology of Canadian Weeds” appeared in the Canadian Journal of Plant Science in July 1972 and it provided a detailed format for the series. Over 110 accounts have been published to date. With the passage of time, there has been a recognized need for an updated format for the series especially to allow for access to other information media that have become available. In addition, much new information has been published since the first accounts in this series appeared; hence there is a need for updated accounts on certain species. The term “weed,” as used in this series, refers to any vascular plant that perpetuates itself in habitats where it is not wanted. Contributions should contain accounts of a single weed species or a group of related species. Offers of contributions by individuals or groups should be made to Dr. P. B. Cavers, Department of Plant Sciences, University of Western Ontario, London, Ontario, N6A 5B7, e-mail pcavers@julian.uwo.ca. These offers of contributions will be subject to approval by a committee set up by the Expert Committee on Weeds, Canada. Approved offers will be subject to re-approval after 3 years. Any inquiries about the format to be used or advice on preliminary drafts should be directed to Dr. Cavers. He will also supply blank maps of Canada and will suggest specialists or institutions that will provide various types of services. The Expert Committee on Weeds (ECW) has initiated a new web site and in the near future authors should find on-line references to common English and French names, links to provincial and federal legislation and current lists of species published and in preparation for this series. The finished manuscript should be submitted to: Canadian Journal of Plant Science, Agricultural Institute of Canada, 141 Laurier Ave. W., Suite 1112, Ottawa, Ontario, Canada KIP 5J3. All contributions must comply with the format of this journal. Accounts on a single species, including all maps, drawings, diagrams and photographs, should not exceed 15 printed journal pages. Of course, accounts on more than one species can be longer.

The effects of two maturation conditions (greenhouse and field) on germination percentages and rates were determined for cypselas (seeds) of Scotch thistle, Onopordum acanthium L. Four coll...

The effects of GA3, KNO3, and NaHCO3 on germination percentages and rates were determined for cypselas (seeds) of four local populations of Scotch thistle, Onopordum acanthium L., collected during a 2-year period. Three (1996, stored cypselas) and four (1997, fresh cypselas) concentrations (0.025, 0.05, and 0.1% for both years, plus 0.0125% for 1997) of the three compounds were used. Both freshly collected cypselas and those stored for 67 days at room temperature exhibited a range of germination responses from readily germinable to strongly dormant. GA3, even at a very low concentration, caused most viable cypselas to germinate, but 5-6% of viable cypselas in two populations did not respond to any GA3 treatment. In general, dry-stored cypselas germinated faster than fresh ones. Populations with more germinability (= proportion of cypselas capable of germinating) responded faster to GA3 than those with less germinability. KNO3 usually increased germination percentages but reduced the rate of germination. W...

To colonize newly disturbed areas, weedy species must disperse their seeds in space and/or in time.Cirsium vulgarehas poor dispersal in space, but can form a persistent seed bank. Fresh seeds are capable of germinating in either light/dark or constant dark conditions under favourable diurnal temperatures of 25°C: 10°C. Despite this lack of dormancy, a large proportion of seeds do not germinate in the autumn after dispersal. Variation in germination requirements according to seed colour was also examined. Fresh seeds were placed under one of two overwintering treatments at 5°C, alternating light/dark or constant darkness. Some seeds of all colours: white, light, intermediate, dark and black germinated under these conditions. Six months later, ungerminated seeds subjected to the light/dark treatment did not require light for germination when placed under optimal temperatures. However, most seeds that had overwintered in constant darkness required light for germination. In the field, this induced dormancy would prevent seeds from germinating if buried or located in deep shade. Such seeds have the potential of forming a persistent seed bank. The proportion of dormant seeds did not appear to be associated with seed colour. Seeds incubated at 10°C following overwintering under light/dark conditions germinated to a higher percentage than seeds overwintered in darkness, regardless of the light conditions for germination. The results of this study help to explain the contradiction between delayed germination in the field and the lack of seed dormancy.

Proso millet (Panicum miliaceumL.) is both a crop and a weed in many parts of the world. The weedy biotypes exhibit a wide range of seed colours, but the strains with the most persistent seeds are distinguished by darker seeds. This paper compares the seed biology of a range of biotypes from Canada and demonstrates that darker seeds have heavier seed coats, imbibe and germinate more slowly, and suffer less imbibition damage (measured as electrolyte leakage). It is concluded that all these attributes contribute to the increased persistence in the soil of the dark-seeded weedy biotypes. Imbibition damage is widely implicated in poor emergence and low vigour of crop seeds, but has not previously been considered in the context of weed seed persistence.

Seeds of Cirsium vulgare were collected from two populations in southwestern Ontario and stored at the site of collection at three depths in the soil. After intervals of 6 to 30 months, seed samples were extracted, the seeds classed as germinated, dead, or firm, and then the firm seeds were set to germinate in a growth cabinet. Both populations established a persistent seed bank when left at the 15 cm depth; however, most seeds do not get buried at great depths. After storage at the surface or 3 cm deep, seeds in an arable sandy soil did not persist beyond 6 months. In contrast, some seeds stored in shaded conditions in a clay loam soil maintained viability for 30 months at die surface and at 3 cm. In some cases, the germination rate of seeds was retarded after storage, especially for seeds that were extracted from soils subjected to wetting and drying before seed retrieval. A separate experiment confirmed that wetting and drying can delay the germination of some seeds of C. vulgare. Key words: seed bank, germination, seed wetting and drying, Cirsium vulgare, bull thistle.

Fall panicum (Panicum dichotomiflorum var. geniculatum), an abundant annual weed in southwestern Ontario, suffers large seed losses from the smut Ustilago destruens. From 19 to 83% of plants were infected in three sites surveyed. Some infected plants were completely sterile, but others produced small numbers of viable seeds. Most of these seeds did not give rise to smut-infected plants if they were not exposed to smut teliospores in the soil over winter. Compared with seeds from uninfected plants, those from infected plants had lower percent viability and weaker dormancy. When seeds from either infected or uninfected plants were mixed with smut teliospores over winter, 39% of the resulting plants were smut infected, compared with less than 1% of plants from seeds overwintered without smut teliospores. Seeds mixed with smut teliospores over winter did not lose viability, but some of them were slower to germinate the following spring. Key words: smut, fall panicum, seed viability, seed dormancy, germination, Ustilago destruens, Panicum dichotomiflorum.

Individual flowering ramets in a large riverbank stand of Saponaria officinalis, bouncingbet, were subjected to three damage treatments at anthesis: removal of most flowers, removal of all leaves, and bending of the stem just below the inflorescence. All seeds were collected from ripened capsules of treated plants as well as from a group shaded by a canopy of Convolvulus sepium and from an untreated control group. Seeds from the defloration treatment were significantly heavier than those from the other treatments. In the control, bent stem, and shaded treatments the seed masses were distributed in a bimodal manner, with most seeds forming a normal distribution around a midpoint of 1.5–1.7 mg and a cohort of heavy seeds having a mean mass of 2.5 mg. This heavy cohort (mode) was missing from the defoliation treatment. Of the total variation in seed mass, 36% was among individuals, 54% was among inflorescences within individuals, and only 10% was within inflorescences. This suggests that resources are allocated differentially between capsules at different positions on the inflorescence but almost uniformly within the individual capsule. Key words: defoliation, defloration, bouncingbet, seed production, Saponaria officinalis.

Summary: Resume: Zusammenfassung The effects of bentazone application on fruit spike length, fruit coat thickness, seed maturation, total number of seeds per plant, seed mass and seed mass distribution in seven populations of Xanthium strumarium from two contrasting habitats were examined. The results showed that variations in fruit traits depended significantly on population and on bentazone treatment but not on habitat. Plants sprayed with bentazone produced significantly fewer fruits that contained at least one developed seed. Bentazone application also reduced mean seed mass in some populations by pushing the seed mass distribution to the small seed side. Spike length and fruit coat thickness are two important traits influencing the probability of seed predation. Bentazone application resulted in shorter spike length in some populations but longer spike length in some others. Fruit coat thickness showed substantial increase after bentazone treatment, suggesting that application of the herbicide may reduce the chance of seed predation. L'effet de traitements herbicides sur les caracteres des fruits dans les populations de Xanthium strumarium L. Les effets de traitements par la bentazone sur la longueur des epis, sur 1'epaisseur des teguments. sur la maturation des graines, sur le nombre total de graines par plante, sur la masse des graines ainsi que sa distribution, ont eteetudies dans sept populations de Xanthium strumarium provenant de deux habitats tres differents. Les caracteres des fruits dependaient significativement de la population et du traitement a la bentazone mais pas de 1'habitat. Les plantes trailees a la bentazone produisaient significativement moins de fruits, qui contenaient au moins une graine developpee. Le traitement par la bentazone reduisait aussi la masse moyenne des graines dans quelques populations en deplncant la distribution des masses vers les faibles valeurs. La longueur de 1'epi et 1'epaisseur des teguments sont deux caracteres importants qui influencent la probabilite de predation de la graine. Le traitement par la bentazone se traduisait par un raccourcissement des epis dans certaines populations et par un allongement dans d'autres. L'epaisseur des teguments augmentait apres un traitement par la bentazone, suggerant que le traitement herbicide pourrait reduire la probabilite de predation. Einflus von Herbizidanwendungen auf die Fruchtbildung von Xanthium strumarium L. An 7 Xanthium-strumarium-Populalionen von 2 unterschiedlichen Standorten wurde der Einflus von Bentazon auf die Rispenlange, die Frucht-schalenstarke, die Samenreifung, die Gesamt-samenzahl pro Pflanze, die Samenmasse und die Samenmassenverteilung untersucht. Die Frucht-merkmale hingen signifikant von der Population und der Bentazon-Behandlung ab. aber nicht vom Standort. Die behandelten Pflanzen brachten signifikant weniger Fruchte mil min-destens 1 entwickelten Samen hervor. Die Be-handlung reduzierte in einigen Populationen auch die mittlere Samenmasse, indem die Samenmassenverteilung zugunsten kleiner Samen verschoben war. Die Rispenlange und die Fruchtschalenstarke sind hinsichtlich moglicher Samenschadigungen wichtige Merkmale. In einigen Populationen verringerte sich nach der Behandlung die Rispenlange, in anderen war sie verlangert. Die Fruchtschalenstarke nahm nach der Behandlung erheblich zu, was vermutlich die Moglichkeit von Samenschadigungen herabsetzt.

Maternal environments have been reported to affect various seed and seedling characteristics in many plants. In this study, we examined the effect of bentazon application to the mother plants on seed germination and seedling emergence of 10 cocklebur populations from wetlands or cultivated land. The mortality or longevity of fully developed seeds was affected significantly by bentazon application. Rate of seedling emergence showed little response, whereas percentage seedling emergence and percentage viable seeds in the soil were reduced by bentazon treatment to the mother plants. Populations from wetlands produced seedlings earlier than those from cultivated land. Key words: Seedling emergence, seed bank, herbicide, bentazon, cocklebur, Xanthium strumarium

Summary: Resume: Zusammenfassung Responses of 10 natural or agricultural populations of Xanthium strumarium to sublethal rates of bentazone applied post-emergence were examined under field conditions. Both vegetative growth and reproduction of sprayed plants were affected by the herbicide. Some populations were more tolerant of bentazone than the others, but the degree of herbicide tolerance did not depend on the previous herbicide experience of a population. Bentazone treatment significantly reduced the weight per fruit in some populations, which in turn could affect the survival and growth of the subsequent seedlings. La reponse depopulations de Xanthium strumarium a des doses subletales de bentazone Nous avons etudie au champ la reponse de dix populations naturelles ou agricoles de Xanthium strumariuma des doses subletales de bentazone appliquee en post-levee. L'herbicide affectait la croissance et la reproduction des plantes traitees. Quelques populations etaient plus tolerantes a la bentazone que d'autres, mais le degre de tolerance ne dependait pas de l'exposition prealable des populations a l'herbicide. La bentazone reduisait significativement le poids des fruits dans quelques populations, ce qui pouvait affecter ensuite la survie et la croissance des jeunes plantes qui en etaient issues. Wirkung subletaler Dosen von Bentazon auf Xanthium strumarium Zehn Herkunfte von Xanthium strumarium wurden im Nachauflauf mit subletalen Dosen von Bentazon unter Feldbedingungen behandelt. Sowohl das vegetative Wachstum als auch die Samenbildung der behandelten Pflanzen wurden durch das Herbizid beeintrachtigt. Einige Herkunfte waren weniger empfindlich, doch der Grad der Herbizidempfindlichkeit stand nicht im Einklang mit fruheren Erfahrungen uber die Wirkung des Herbizids. Durch die Bentazon-Be-handlungen nahm das Gewicht der Samen bei einigen Herkunften signifikant ab, so das ihre Lebensfahigkeit und das Wachstum der Keimpflanzen beeintrachtigt sein konnten.

Seven populations of Xanthium strumarium L. collected from wetlands and arable fields were examined for their responses to three levels of bentazon application. Significant differences were observed among populations for all traits measured. Contrasts between the wetland and arable populations indicated significant differences in some traits, especially the length and width of the fifth internode. These measurements are closely related to plant biomass, and they were reduced greatly in the wetland populations after bentazon treatment. However, an overall comparison using canonical discriminant analysis failed to show differences between the wetland and arable populations, suggesting that differences in response to herbicide between the two ecotypes may be due to changes in a few traits relating to fitness. Key words: Growth, weed, herbicide, bentazon, cocklebur, Xanthium strumarium

Proso millet has become a major weed in North America during the past 20 yr. Experiments were conducted to assess the role of the soil seedbank in proso millet's success as a weed. Proso millet has at least eight distinct biotypes, all weeds, which exhibit a wide range of seedbank behavior. At one extreme, weed biotypes resembling crop varieties form transient seedbanks where all viable seed germinate or die before newly ripened seed enter the seedbank. In contrast, the black- and dark-red-seeded biotypes form persistent seedbanks that last several years in the soil. These latter seedbanks differ from those previously described in that there is always a fraction of the seedbank that is not capable of immediate germination. The black-seeded biotype of proso millet can establish a persistent seedbank quickly and that makes the weed very difficult to eradicate.

Helianthus tuberosus L., Jerusalem artichoke, is a native perennial tuber-producing weed. In Canada, its range extends from the Maritimes to the Pacific coast, but it is primarly found in southern Ontario and Manitoba. A cultivated form has been grown commercially in Ontario and western Canada for use as a human food source, for livestock feed and for the production of a variety of chemical products such as ethanol. As a weed, H. tuberosus competes vigorously with grain and field crops, but does not readily invade arable land except as a volunteer crop. The high carbohydrate content of H. tuberosus tubers, coupled with multiple regenerative strategies featuring seeds and tuber-bearing rhizomes, can lead to rapid population increases under favorable conditions.Key words: Helianthus tuberosus, Jerusalem artichoke, weed biology

Three plants from each of 10 populations of the black biotype of proso millet (Panicum miliaceum) were grown in a common garden in London, Ontario. Seeds were collected from individual plants as they ripened. Each seed was identified as to location on the plant and weighed separately. Mean seed weight decreased over the growing season, both on individual inflorescences and on entire plants. Despite this trend, seeds at the upper end of the weight range were produced throughout the season. The decline in the mean resulted from an increasing proportion of smaller seeds. There was also increased variability in seed weight later in the growing season. In subsequent germination tests there was no discernable relationship between total percent viability and date of seed ripening. Total percent viability was above 70% for each sampling date. Key words: seed weight, positional effects, proso millet, germination, seasonal variation.

Barbarea vulgaris R.Br. is an introduced weed of recently disturbed areas, small-seeded grain crops, roadsides and pastures. It is abundant in southern Ontario, Quebec and the northeastern U.S.A.; frequent in the Maritimes, British Columbia and the northwest coastal U.S.A.; and rare south of 33°N, north of 50°N and across the prairies. The weediness of this species largely results from its prolific seed production, enforced and induced seed dormancy, and its rapid growth under favourable conditions. Key words: Barbarea vulgaris, yellow rocket, weed biology

Seedlings of proso millet usually were kiRled by discing and rototilling in field experiments but populations were not reduced by mowing or by compressing under tractor wheels. In greenhouse experiments, recently emerged seedlings had the greatest mortality after raking and desiccation treatments but were less affected by shoot and/or root damage. In contrast, seedlings treated several weeks after emergence suffered greater mortality from shoot damage and less from desiccation. Two weedy proso mllet biotypes, black and Crown, were used in the field experiments, and up to six biotypes were used in the greenhouse. Few significant differences among biotypes were found. Young (emerging) seedlings were extremely resilient to all treatments. Nomenclature: Proso millet, Panicum miliaceum L. #3 PANMI. Additional index words: Mowing, rototilling, disc harrowing, desiccation, PANMI.

Approaches used to study seed banks and early publications on them are summarized. Current areas of interest are described, including the balance between herbicide-susceptible and herbicide-resistant seed populations, the effects of reduced tillage, the genetic structure of the seed bank, the role of desiccation, the impact of nutrients, oxygen and ortho-dihydroxyphenols, and methods of sampling seed banks and processing the data.

Cypsela dormancy in Scotch thistle (Onopordum acanthium) may be affected by the presence of chemical inhibitors. To investigate this phenomenon, a leachate from O. acanthium cypselas was tested for its ability to inhibit germination of the cypselas from which it was derived (i.e., autoinhibition). Leachates varied in their degree of autoinhibition, depending on the cypsela population from which they were prepared. Overall, removal of leachate from a group of O. acanthium cypselas increased their germinability. Using lettuce (Lactuca sativa) cypselas as an indicator species, bioactivity-guided fractionation was used to isolate a water-soluble, para-substituted benzamide from O. acanthium cypselas, which caused germination inhibition. Various chromatographic, spectroscopic, and spectrometric techniques were applied to the characterization of the bioactive compound.

In order to assess the capacity for in vivo fluorescence spectroscopi8c analysis of arterial collagen and elastin, fluorescence emission intensity was recorded form rabbit aorta after angioplasty and stent implant, and correlated with extracted elastin and collagen content. FEI from saline treated rabbits after stent implant was higher between 485 and 500 nm than after anti-inflammatory treatment. FEI was significantly decreased after implantation of shorter stents at 476-500 nm. Multiple regression analysis demonstrated an excellent correlation between FEI and elastin and HPLC- measured collagen content at 486-500 nm and 476-480 nm respectively. Conclusions: FEI recorded in vivo form arterial intimal surface, can be successfully used for quantitative assessment of compositional changes in connective tissue. Stent implant can induce changes in intimal arterial structure at discrete sites distant from the stent implant site.© (2002) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

Altered collagen and elastin content correlates closely with remodeling of the arterial wall after injury. Optical analytical approaches have been shown to detect qualitative changes in plaque composition, but the capacity for detection of quantitative changes in arterial collagen and elastin content in vivo is not known. We have assessed fluorescence spectroscopy for detection of quantitative changes in arterial composition in situ, in rabbit models of angioplasty and stent implant. Fluorescence emission intensity (FEI) recorded at sites remote from the primary implant site was correlated with immunohistochemical (IH) analysis and extracted elastin and collagen. FEI was significantly decreased (P or=0.961) analysis were detected by multiple regression (MR) analysis. Good correlations also were found for FEI with elastin and collagen measured by high-performance liquid chromatography; MR analysis provided highly predictive values for collagen and elastin (R2>or=0.994). Fluorescence spectroscopic analysis detects quantitative compositional changes in arterial connective tissue in vivo, demonstrating changes at sites remote from primary angioplasty and stent implant sites.

1. Seed input, changes in the seed bank and seedling recruitment of Onopordum were monitored over 1 year at three contrasting sites (pasture, oat crop and hillside) within an 80-hectare paddock at Galong, New South Wales, about 100 km NW of Canberra. Each site was c. 2000 m 2 . Time constraints precluded a longer study and repetition of the sampling procedures at similar sites in other areas. 2. In the pasture there were few Onopordum plants but a seed bank of c. 5000 seeds m -2 . During the year the seed bank decreased by more than half, but the most dormant component remained constant at c. 800 seeds m -2 . 3. In an oat crop nearby there were no flowering Onopordum plants and there was no direct seed input. Nevertheless, the seed bank of c. 700 seeds m -2 did not decrease. 4. At the third site, a grazed hillside, Onopordum density was high (19 plants m -2 ). The seed input of 1788 seeds m -2 caused a temporary small increase in the seed bank in summer but there was no change over the 1-year period either in the total seed bank (c. 3000 seeds m -2 ) or in its most dormant component (c. 750 seeds m -2 ) . 5. Seedlings appeared in all seasons, invariably after rain. More than 95% of seedlings appeared in late summer or autumn, but different management practices changed the pattern of winter establishment. 6. For ecological studies of weeds, the population dynamics of the seeds in the soil and of the plants above ground are equally significant. This study shows that the existence of a small pool of labile seeds (c. 15% minimum) in the seed bank that can be recruited opportunistically, together with a large, strongly persistent component, will make any form of short-term control difficult.