Showing papers on "Seedling published in 1982"

Distribution Ecology: Variation in Plant Recruitment over a Gradient in Relation to Insect Seed Predation

Abstract: Although predispersal seed predation by insects is common, no test exists of its effect on plant recruitment. This study examines seed predation in the population dynamics of a native, temperate shrub, Haplopappus squarrosus H. and A. (Asteraceae), over an elevational gradient in the coastal sage scrub vegetation of San Diego County, California USA. Frequency and abundance of H. squarrosus increase from coast to mountains. Expected abundance, based on flowers initiated, was highest at the coast and lowest in the interior, the opposite of the observed adult plant distribution. Overall flower and seed predation by insects was high (44-73%) and was greatest at the coast. Insect exclusion experiments at sites along the gradient had three main results. (1) Seedling recruitment was proportional to the number of viable seeds after seed predation. The exclusion plots had significantly higher numbers of seedlings established at all sites than did control plots; the greatest increase was at the coast. (2) Seedling survivorship was independent of both seedling and adult densities. (3) Juvenile recruitment was proportional to seedling establishment. Predation by insects prior to release of seeds played a critical role in the population recruitment of H. squarrosus within and among sites along the gradient. Survivorship of established plants, in addition, was as high at the coast as it was in the interior. These results suggest that indigenous insect seed predators can be a major force controlling the dynamics of a native plant species over its natural distributional range.

The Effects of Low Temperature on Zea mays

Abstract: Publisher Summary This chapter describes various physiological effects of low temperature on maize and evaluates their significance for maize growing and breeding. A distinction has been made between low-temperature damage and the effects of suboptimal temperatures above the injury threshold on growth rate and the processes underlying it. Maize is sensitive to frost in all phases of its growth cycle except as dry seed. Freezing injury depends on the temperature, the duration of freezing, the water status of the plant, and the stability of supercooled water. Temperatures below and around the minimum temperature for germination and growth cause various types of physiological damage in maize. These low-temperature effects are referred to as chilling injury. Low-temperature chlorosis occurs at temperatures above the chilling range. Seeds and seedlings are sensitive to various types of injury. Soil fungi cause seed rot and seedling blight. Several types of physiological damage may occur, such as freezing injury, chilling injury, and low-temperature chlorosis. Low temperatures not only retard germination, emergence, and vegetative growth, but also affect morphogenesis. The chapter presents evidence showing that seedling growth at suboptimal temperatures is limited by leaf and root extension rather than by photosynthesis or the uptake of water and mineral nutrients.

Effects of seed size on seedling size in Virola surinamensis; a within and between tree analysis.

Abstract: We conducted a greenhouse study of the effects of initial seed mass on seedling characteristics in a Panamanian population of Virola surinamensis, a canopy tree in which mean seed mass of different individuals ranges from 134 to 404g The system is of particular interest because birds preferentially eat fruits of small-seeded plants, leaving seedlings of large-seeded individuals under conditions of potentially severe sibling competition (Howe and Vande Kerckhove 1980) Effects of differences of mean seed mass between trees are explored using an analysis of variance, while effects of seed-mass variation within crops are demonstrated with a regression analysis A two-way analysis of variance decisively shows effects of parental source and light condition on seedling height, leaf length, and dry shoot mass (all P<00001) A posteriori tests show that differences in seedling characteristics reflect differences in initial seed mass, with especially strong differences apparent in shoot mass Regression of seedling characteristics on initial seed mass shows that variation of seed size within a crop is sufficient to influence shoot mass at 15 weeks (P<00001) Effects of size differences of seeds that land adjacent to each other, either under the parent or in monkey droppings, are documented with growth of pairs of seedlings in pots Differences in shoot height and mass at 15 weeks are evident when seeds of average size differ by only 02 g, and dramatic differences are evident when paired seeds differ by an average of 15 g Seedlings grow more when isolated than when planted with conspecifics These experimental results offer indirect support for the hypothesis that small-seeded Virola parents secure an advantage in reproduction through differential dispersal, while large-seeded plants produce more competitive seedlings under their own crowns — an advantage most likely to be of importance when frugivores are scarce

Toxicity of Aluminum to Coffee Seedlings Grown in Nutrient Solution

Abstract: A solution culture experiment was conducted with coffee seedlings (Coffea arabica L.) to determine the combined effect of ionic strength and aluminum (Al) concentration of nutrient solutions on Al availability. The treatments consisted of three Al concentrations: 0.0, 0.037, and 0.148 mmol dm⁻³. These were combined with five levels of ionic strength produced by diluting a complete nutrient solution to relative concentrations of 0.5, 0.25, 0.10, and 0.01. The phosphorus (P) concentration of each solution was adjusted to 0.1 mmol dm⁻³. The pH of the solutions was maintained at 4.0 ± 0.2. Shoot and root growth decreased progressively under the Al treatments. The lateral roots of Al-stressed plants were thicker, shorter, and fewer in number than those of the control plants. The younger leaves of Al-stressed plants were small, curled along the margins, and frequently chlorotic along the leaf margin. At a constant Al concentration, seedling growth was reduced with dilution of the nutrient solution. This decrease in growth was best correlated with an increase in the activity of Al³⁺. An Al³⁺ activity value of 1.2 × 10⁻⁵ was associated with a 10% reduction of coffee seedling growth.

The effects of propagule size on germination and seedling growth in Mirabilis hirsuta

Abstract: Mirabilis hirsuta, a fugitive prairie plant species, occurs only on disturbances (mounds) resulting from the foraging activity of badgers on the Cayler Prairie Preserve in northwestern Iowa, U.S.A. Seedling survivorship and later competitive success are predicated upon the root's rapid extension to and occupation of a moisture-retentive layer of buried vegetation which forms the base of these disturbances. Seed size, which varies from 6 mg, is a predictor of the likelihood of establishment success through effects upon germination and seedling vigor. Regressions indicated that germination increased by 10.2% per milligram increase in seed weight, leaf area of 30-day-old seedlings increased by 47.8 mm2/mg seed weight, and dry weight biomass of these seedlings increased 40.2 mg/mg seed weight. Germination also occurred more rapidly with heavier seeds. Differences in seedling growth with increases in seed size are largely due to the capital provided by initial food reserves. The instantaneous rate of in...

Plant Growth and Survival under Strict Anaerobiosis

Abstract: Anaerobic incubation of seedlings and rhizomes reveals interspecific differences in the ability of seedlings and rhizomes of higher plants to survive under prolonged and strict anaerobiosis. Rhizomes of several species were killed by an anaerobic incubation at 22 °C for 7 d while others survived and showed normal shoot extension on return to aerobic conditions. A third group of species showed healthy and geotropically normal bud and shoot extension while their rhizomes were in the oxygen free environment. A detailed comparison of bud and shoot growth rates was made with Scirpus maritimus under aerobic and anaerobic conditions over a 14 d period. Under similar conditions four species of grass seedlings were subjected to anaerobic conditions for 2-8 d at 5 °C, 15 °C and 25 °C. Seedling mortality was highest at 25 °C in all four grasses. Interspecific differences were evident. The wetland species were more tolerant of anoxia than the

Adaptation of gray squirrel behavior to autumn germination by white oak acorns.

Abstract: The oaks (Quercus L.) are divided into two subgenera, the white oaks (Leucobalanus Engelmann) and the red oaks (Erythrobalanus Spach). Like most midlatitude plants, red oaks have dormant seeds which germinate in spring after being dispersed in autumn. Acorns of many species of white oaks germinate in autumn soon after they fall, producing a large taproot which stores much of the acorn's food reserves over winter. Live (evergreen) oaks are taxonomically regarded as red oaks (Williams, 1939), but resemble white oaks in many important seed and life history traits, including early germination (Sargent, 1905; Lewis, 1911; Trelease, 1924; USDA, 1974). Red oaks and white or live oaks typically occur together as associates and potential competitors throughout North America. They will be referred to collectively as WO and RO; WO by implication includes live oaks insofar as their seed biology is convergent with white oaks. Unabbreviated common names refer to single species for which the scientific name is given at least once. The seedling taproot of white oak (Q. alba L.), probably the most common WO of eastern North America, grows rapidly in autumn and perhaps also grows more slowly through the winter, drawing upon the food reserves of the cotyledons. The seedling taproot is remarkably thickened on seedlings of Q. alba and Q. virginiana Mill. (Fig. 1A; Lewis, 1911) and appears to serve as an overwinter storage organ. A white oak acorn in a sense buries itself, and the rapid germination and root engorgement may serve as an escape from various seed predators (D. H. Janzen, pers. comm.). This paper reinterprets autumn germination in the WO as a post-dispersal escape from tree squirrels, although the trait may have other adaptive values as well. It also reports that gray squirrels (Sciurus carolinensis Gmelin) kill acorns of WO before caching them, by cutting out (excising) the seed 'embryo' (Fig. 1B, C). The adaptive value suggested for this behavior is preventing 'escape' and loss of that fraction of the acorn which is transferred into the seedling taproot between the time an acorn is cached in autumn and the time when a squirrel returns to utilize the acorn in winter. A brief description of oak seed and seedling morphology will be helpful (see also USDA, 1974 p. 698). The mature acorn, technically a fruit but here called a seed, consists of a pericarp (shell) enclosing two seedling leaves (cotyledons) which are filled with food reserves and occupy most of the seed. The cotyledons are connected by petioles to the tiny seedling (hereafter improperly but less ambiguously called the embryo when referring to ungerminated acorns). The embryo is located very near the apex or pointed end of the acorn and is folded between the cotyledons. In germination the pericarp splits at the apex and the radicle (seedling root) emerges first. Later, the entire seedling is thrust out, as the cotyledonary petioles arch out and downwards and lengthen to 2-5 cm. The radicle grows into a stout taproot in autumn, but the epicotyl and hypocotyl (the presumptive leaves and stem) grow scarcely at all until spring.

Allelopathic potential of wheat (Triticum aestivum) straw on selected weed species.

Abstract: The allelopathic potential of wheat (Triticum aestivum (L) 'Doublecrop') straw residue was evaluated on weed-seed germination and seedling growth The in- hibition of weed-seed germination and seedling growth was extract-, species-, and temperature-dependent The extracts prepared by agitating and soaking caused greater inhibition than those obtained by leaching The descending order of species susceptibility was ivyleaf morningglory (Ipomoea hederacea (L) Jacq), velvetleaf (Abutilon theophrasti Medic), pitted morningglory (Ipomoea lacunosa L), hemp sesbania (Sesbania exaltata (Raf) Cory), sicklepod (Cassia obtusifolia L), and Japanese barnyard millet (Echinochloa crus-galli var frumetaceae (Roxb) Link) Incubation at 35 C caused the greatest inhibition of germination and growth Additional index words Seed germination, germination temperature, phytotoxicity, seedling growth

Germination of the dimorphic fruits of bidens pilosa l.

Abstract: SUMMARY Dimorphic fruits of Bidens pilosa were tested separately for differences in germinability and seedling development. The long achenes were found to germinate readily under a wide range of conditions while the short achenes showed fairly exacting germination requirements. Germination of the short achenes was found to be enhanced by red light treatment, scarification, applied hormones, leaching and increased oxygen tensions. Seedlings originating from short achenes showed lower survival rates and initially slower development than those originating from the long achenes. The implications of the morphological differences and differences in germination and development of the two achenes are discussed.

Factors influencing seed weight in Impatiens capensis (Balsaminaceae)

Abstract: I analyzed withinand between-plant variation in seed weight from one greenhouse and four natural populations of Impatiens capensis Meerb. Most variation in seed size in natural populations occurred within populations and within plants. Weights of seeds from cleistogamous flowers on greenhouse plants increased with height on the plant and proximity to the main stem, a result that may be related to the local supply of photosynthate. Mean seed weight in the natural populations declined during seed set, then increased again. Seeds from chasmogamous flowers were significantly larger in one of the four populations. Maternal parents differed significantly in both mean seed weight and the relative size of the two types of seeds. Combined genetic and general environmental effects accounted for 26% of the total phenotypic variance, which provides an outside estimate of the heritability of this character. COMPARISONS OF SEED WEIGHT between plant species have revealed an extreme range of variation, while seed weight within a species remains roughly constant despite great variation in overall plant size (Harper, Lovell and Moore, 1970; Harper, 1977). Salisbury (1942) and Baker (1972) investigated variation in seed weight between species and found larger seeds in species colonizing dry and/or shady habitats. They suggested that increased resources were required to initiate growth in these habitats, and that within a habitat, demands of various dispersal mechanisms also affected seed size (Salisbury, 1975). Smith and Fretwell (1974) modelled this general relationship and predicted that increased seed size should be favored under harsh conditions. Comparisons of seed size within a species have shown more subtle variation within and between populations. Some of this variation is attributable to the same selective forces that influence seed size between species. Thus, populations growing at higher plant densities, with increased shade and root competition, often produce larger seeds (Solbrig and Simpson, 1974; Werner and Platt, 1976). Such variation is adaptive because even these relatively minor differences in seed size within a species are capable of producing substantial differ1 Received for publication 17 July 1981; revision accepted 21 January 1982. I thank B. Klehr for her assistance in this study. R. Sweeney, J. Hickman, and an anonymous reviewer contributed many helpful suggestions on the manuscript. T. Mitchell-Olds pointed out how the data could provide an outside estimate of heritability. ences in seedling performance (Black, 1958; Henson and Tayman, 1961; Stickler and Wassom, 1963; Cope, 1966; Harper et al., 1970; Williams, Black and Donald, 1968; Gross and Soule, 1981). Demands of wind or animal dispersal or predation (Janzen, 1977; Hare, 1980) may also favor adaptive changes in seed size within species. Maun and Cavers (1971) investigated variation in seed within individual plants of Rumex crispus, and found considerable variability, indicating an appreciable degree of phenotypic plasticity (environmental variance) for this trait. The seeds produced at the tips of the distal branches within the panicle were smaller than seeds on more proximal branches near the base of the inflorescence. Within-species variation in seed weight, then, has both genetic and environmental components. Differences between populations and individuals reflect both of these components, but variation within a plant can only reflect environmental variance. This environmental variance could result from either developmental instability or genetically based adaptive variability, but these are very difficult to distinguish (Hickman, 1979). Only in species incapable of adjusting the number of seeds after their initiation would it be obvious that changes in physiological status would lead to nonadaptive variation in final seed weight. I here report the results of an investigation into variation in seed weight in Impatiens capensis Meerb. (= I. biflora Walter = I. fulva Nuttall [Fernald, 1950]), orjewelweed, an herbaceous annual that produces both cleistogamous and chasmogamous flowers. Jewelweed is capable of colonizing a wide variety of hab-

Seed banks and seedling occurrence in a high Arctic oasis at Alexandra Fjord, Ellesmere Island, Canada

Abstract: The sizes and floras of the seed banks and seedling communities are described for a variety of habitats in a high Arctic lowland oasis on Ellesmere Island, located at 79° N latitude Four disturbed habitats had larger seed banks than did four undisturbed habitats (averaging 3070/m2 vs 63/m2) The seedling densities measured in the disturbed habitats were also larger (1780/m2 vs 180/m2) The data indicate that sexual reproduction is important to the herbaceous, short-lived, ruderal species which colonize disturbed sites in the high Arctic This contrasts with the more conservative strategy of stress-tolerant species that occur in relatively closed and undisturbed habitats, which tend to propagate by vegetative mechanisms

Studies on the population biology of the genus Viola. IV. Spatial pattern of ramets and seedlings in three stoloniferous species.

Abstract: (1) The spatial pattern of demographic variables of ramets and seedlings in sixteen populations of Viola blanda, V. pallens and V. incognita were analysed using a variety of approaches (area and distance methods, G-tests of heterogeneity based on area counts, neighbourhood analysis, spatial autocorrelation). The variables considered were the position of ramets in space and time, emergence and mortality of ramets and seedlings. (2) Emergence of new seedlings is clumped in space. The seedlings tend to be more numerous in areas where the overall ramet density is low, indicating that seed germination or seedling emergence or both are inversely correlated with overall density of ramets. Seedling survival is affected by density. (3) Ramets one-year-old or older appear to be aggregated or randomly distributed in space. (4) The pattern of emergence of new ramets from stolons and the pattern of ramet death is random in space and not density dependent. (5) It is proposed that seedling germination or survival or both are density dependent, but that the pattern of adult ramet distribution, vegetative production of new ramets and ramet mortality is more sensitive to environmental variables such as light, water and nutrients which are known to be unevenly distributed on the forest floor. (6) The concept of 'safe site' for seed germination has little predictive value in these populations of Viola.

Post-fire regeneration strategies of Californian coastal sage shrubs.

Abstract: Regeneration methods for coastal sage srub vegetation after fire were studied in the coastal Santa Monica Mountains of southern California. Six sites were sampled two years after a large fire of fall, 1978. The intensity of fire varied. Foliar cover and flowering incidence were recorded for individuals regenerating by resprouting or from seed. Resprouting plants contributed most to post-fire recovery, comprising 95% of the relative foliar shrub cover; 84% of resprout and 47% of seedling cover had flowered. An ANOVA of reproductive mode and fire intensity indicates that resprout total cover and individual size are significantly greater than those of seedlings, regardless of fire intensity. Among sites the average foliar cover of resprouts exceeded that of seedlings by factors ranging from 9 to 63. All coastal sage species examined resprout, although the potential vigor of resprouting appears to vary widely within genera (e.g. Encelia, Eriogonum, and Salvia) and even within species. In the second growing season following fire seedling density increased due to seeds shed by resprouted shrubs. Most of the cover on these stands of coastal sage scrub is destined to be either crown-sprouted individuals or their progeny.

Effects of pine-produced chemicals on selected understory species in aPinus ponderosa community.

Abstract: Pinus ponderosa accounted for more than 98% of all tree and shrub stratum stems in a climax community with low herb coverage and aboveground biomass, 35% and 60 g/m(2), respectively. Because of our previous report that nitrification and nitrifying bacteria in the same community were allelopathically inhibited, we speculated that the pine-produced allelochemics might also directly influence the development and growth of the herb stratum. In most cases decaying needles, needle leachate, and field soils significantly reduced germination and radicle growth ofAndropogon gerardii andA. scoparius, pine-associated herbaceous species. Additionally, growth ofAndropogon scoparius seedling radicles was reduced 28-56% by pine needle extracts, 33% by pine bark extracts, and 67% by soil hydrolysate extracts.Andropogon seed germination was reduced 20-25% by pine needles and soil. Phytotoxins identified in various plant parts and associated soils were caffeic acid, chlorogenic acid, quercetin, and condensed tannins. Pine needle water and soil hydrolysate extracts were most inhibitory to the radicle growth of the test species. Thus it appears that the limited growth of the herbaceous stratum in the pine community may be accounted for, in part, by allelopathy. Such allelopathic interactions may have an adaptive ecological significance in various forest and other plant communities.

The Influence of Vesicular-Arbuscular Mycorrhizae on the Growth and Development of Eight Hardwood Tree Species

Abstract: Eight hardwood forest species were grown in fumigated soil without vesicular-ar­ buscular mycorrhizal (YAM) fungi or in soil infested with either Glomus fasciculatus (GF), a mixture of Glomus mosseae and G. etunicatus (GM), or a mixture of several fungal species in the genera Glomus and Gigaspora (GG). With the exception of sugar maple, YAM development increased stem weight of seedlings by 2- to SO-fold over nonmycorrhizal controls. Root weight of all seedlings was increased by 4- to 70-fold by YAM. Generally, GF stimulated more seedling growth than other fungi. Laboratory assays of the root samples indicated that feeder root infection by the fungi varied from 55 to 85 percent, but generally there were no significant differences among the YAM treatments within tree species. Differences among hosts were observed in the amount of hyphae, arbuscules, and vesicles produced by the fungi, which could be attributed to growth and development characteristics among hosts and YAM fungi. The data suggest that high­ quality seedling stock of these hardwood tree species can be obtained in nurseries where cultural practices in the nursery encourage YAM development. FoREST Sci. 28:531-539.

Association with mature plants protects seedlings from predation in an arid grassland shrub, Gutierrezia microcephala.

Abstract: Survivorship of Gutierrezia microcephala (Compositae) seedlings was studied in an undisturbed arid grassland and in experimental plots where various components of the natural vegetation were removed following seed germination The major causes of seedling mortality were herbivore damage from the specialist grasshopper, Hesperotettix viridis, and drought stress associated with competition from established plants The relative intensity of these mortality factors varied strongly with seedling size Large seedlings had higher overall survivorship but were most likely to be killed by defoliation; most small seedlings died of drought stress In plots where all perennial grasses were removed (leaving established G microcephala plants), seedling survivorship was 5 times greater than in undisturbed vegetation Surviorship in plots where both grasses and mature G microcephala were removed was slightly poorer than in undisturbed vegetation due to a large increase in mortality from defoliation From May–August, when the herbivore H viridis was abundant, seedling survivorship was better in the immediate vicinity of mature conspecific plants than in plots lacking mature G microcephala, both in the presence and absence of perennial grasses These results provide a counter example to theories predicting that the impact of specialist herbivores on seedling recruitment is greatest in the vicinity of parent plants

Development of 1-O-sinapoyl-β-D-glucose: L-malate sinapoyltransferase activity in cotyledons of red radish (Raphanus sativus L. var. sativus).

Abstract: Protein preparations from cotyledons of red radish (Raphanus sativus L. var. sativus) catalyzed the the formation of depsides between cinnamic acids and L-malate, using 1-O-acyl glucose conjugates as the donors. This activity showed an absolute acceptor specificity towards L-malate and a pronounced donor specificity with 1-sinapoylglucose (1-O-sinapoyl-β-D-glucose). Maximal rate of sinapoyl-L-malate formation was found to be at pH 6.3, and there was no requirement for metal ions or sulfhydryl group reagents. The K m values were found to be 0.46 mM for 1-sinapoylglucose and 54 mM for L-malate. Protein extracts obtained from seedlings at different stages of seedling development did not significantly differ with respect to the properties of the enzymatic activity. Appearance and development of extractable activities correlated well with the in vivo transacylation kinetics of 1-sinapoylglucose to sinapoyl-L-malate during seedling growth. Maximal activity was extracted from 10–14-d-old seedlings and found to be at 67 pkat pair-1 of cotyledons. This new enzymatic activity in phenylpropanoid metabolism refers to an enzyme which can be classified as 1-sinapoylglucose: L-malate sinapoyltransferase (SMT) (EC 2.3.1.-).

Growth and Development of Silverleaf Nightshade (Solanum elaeagnifolium)1

Abstract: Controlled - environment studies were conducted to determine the influence of temperature, light, seed weight, depth of planting, substrate pH, and salinity on the germina- tion and emergence of silverleaf nightshade (Solanum elaeagni- folium Cav.). The effects of planting date, top removal, and root-cutting length on establishment were studied in the field. Fluctuating temperatures of 20 to 30C produced 57% germination. Maximum germination, 59%, occurred between pH 6 and 7. NaCl concentrations greater than 2500 ppmw caused germination to decrease 85% or more compared to the control. Light was not important for germination. Mean seedling emergence was 46% from depths of 1.0 to 2.5 cm. Silverleaf nightshade seedling emergence from a 2-cm depth was 31% greater in a sandy soil than a loam. Delayed seeding caused a decline in dry-weight accumulation of above-ground parts. Fifteen percent of seedlings clipped 15 days after emergence were capable of regrowth, and after 30 days or more, 90% of the clipped plants regrew. Additional index words. Planting date, top removal, root length, planting depth, salinity.

Use of the ectomycorrhizal fungus Laccarialaccata in forestry. I. Consistency between isolates in effective colonization of containerized conifer seedlings

Abstract: Four isolates of the ectomycorrhizal fungus Laccarialaccata (Scop. ex Fr.) Berk and Br. were inoculated singly onto containerized Douglas-fir (Pseudotsugamenziesii (Mirb.) Franco), ponderosa pine (Pinusponderosa Dougl. ex Laws.), Sitka spruce (Piceasitchensis (Bong.) Carr.), and western hemlock (Tsugaheterophylla (Raf.) Sarg.) seedlings to detect ecotypic variation in colonization success and effects on seedling growth. All isolates formed well-developed ectomycorrhizae on all inoculated seedlings. Abundance ratings of short roots colonized did not differ between the four isolates for any conifer species; most inoculated seedlings developed ectomycorrhizae on over 80% of their short roots. There were also no differences between isolates in affecting seedling height, stem diameter, and dry weight of tops and roots for all conifer species. Inoculations did not improve seedling growth over uninoculated controls. Uninoculated controls of Douglas-fir and ponderosa pine had significantly greater dry weight than...

Invasion by Pittosporum undulatum of the forests of Central Victoria. II Dispersal, germination and establishment

Abstract: Invading Pittosporum undulaturn tends to be clumped around the butts of established trees. This is due to the preferential deposition of seeds in these sites by the European blackbird (Turdus merula) which is believed to be the main vector of dispersal. Native silvereyes (Zosterops lateralis) eat some seed but are not considered important in dispersal. The high mortality of seedlings in exposedsites reinforces the patchy pattern originally dictated by seed dispersal. Seeds may germinate after seed fall in spring but most seeds germinate in autumn. No seeds germinate during summer because of the low rainfall and high temperatures, the optimum germination temperature being 18-21 OC. After 16 months' storage at moderate temperatures and humidities, 80% of seed was still viable but viability was reduced to 30% at very low humidities. Seedlings of P. w2dulatum have three growth stages. The juvenile and transitional stages last 6-12 months and have alternate leaves. In the adult phase a terminal vegetative bud forms at the stem apex. Bud burst may occur several times a year in seedlings and twice a year in fruiting adults. The seedling root habit varies with soil type. The seedlings are able to coppice if the shoot is removed. P. undulatum is an aggressive invader of eucalypt forests despite the poor survival of the initial colonizers. The formation of a regeneration niche ensures the survival of succeeding generations. Consequently, P. undulatum is a permanent threat to the Victorian vegetation.

Seedling density and seedling survival in Alaskan cotton grass tussock tundra

Abstract: Previous workers have suggested that reproduction by seedling establishment is less important in the maintenance of tundra vegetation than in temperate areas, but few quantitative data are available. Seedling densities were studied at 11 tundra sites in or near disturbed and undisturbed cotton grass tussock tundra in Alaska, and numerous seedlings were found. Examination of seedling age structures suggests that at least Ledum palustre and probably also Empetrum nigrum do replace themselves by seed in undisturbed tundra. Seedling densities vary greatly depending on the substrate available for establishment.

Seedling growth and yield response of flax, buckwheat, sunflower and field pea after preseeding magnetic treatment

Abstract: Dry seeds of flax (Linum usitatissimum L.), buckwheat (Fagopyrum esculentum Moench.), sunflower (Helianthus annuus L.) and field pea (Pisum sativum L.) were given brief magnetic exposure prior to germination. Seed of high and low germination potential were grown in petri dishes at 10 and 20 °C. A small number of seed lots produced earlier and more vigorous seedling growth as a result of magnetic treatment, but the differences were small and inconsistent. In the field, there were no improvements in yield from magnetic seed treatment in three out of four years. In one year there was a significant increase in yield for sunflower.