Showing papers on "Germination published in 1981"

A comparative study of germination characteristics in a local flora

Abstract: seeds for immediate germination. Of the 403 species examined, 158 failed to exceed 10% germination but 128 attained values greater than 80%. Germination was high in the majority of grasses and low in many annual forbs and woody species. With respect to initial germinability, major families could be arranged in the series Gramineae > Compositae > Leguminosae = Cyperaceae > Umbelliferae. Many small-seeded species were able to germinate immediately after collection and seeds of these species were often elongated or conical and had antrorse hairs or teeth on the dispersule. High initial germinability was conspicuous among the species of greatest abundance in the Sheffield flora. (4) In the majority of species, germination percentage increased during dry storage; this effect was most marked in small-seeded species. Among the seventy-five species which responded to chilling, some germinated at low temperature in darkness whilst others were dependent upon subsequent exposure to light or to higher temperature or to both. Responses to chilling were characteristic of the Umbelliferae. In all of the legumes examined, rapid germination to a high percentage was brought about by scarification. (5) Under the experimental conditions, all of the annual grasses showed the potential for rapid germination. High rates were also observed in many of the annual forbs and perennial grasses. Low rates of germination occurred in the majority of sedges, shrubs and trees, and were particularly common in species of northern distribution in Britain. Rapid germination was characteristic of the species of greatest abundance in the Sheffield flora. Rate of germination showed a progressive decline with increasing seed weight, and, with some exceptions, there was a positive correlation between rate of germination and the relative growth rate of the seedling. (6) In sixteen species, germination in the light was found to be dependent upon exposure to diurnal fluctuations in temperature. Under constant temperature conditions, the majority of grasses, legumes and composites germinated over a wide range of temperature, and the same feature was evident in species of ubiquitous or southern distribution in the British Isles. A requirement for relatively high temperature was apparent in sedges, in plants of northern distribution and in a majority of the marsh plants. The range of constant temperatures conducive to germination tended to be wider in grassland plants than in woodland species. Rapid germination over a wide range of temperature occurred in many of the species which attain greatest abundance in the Sheffield flora. 0022-0477/81/1100-1017 $02.00 (?1981 Blackwell Scientific Publications

Development and storage-protein synthesis in Brassica napus L. embryos in vivo and in vitro

Abstract: Immature embryos of Brassica napus were cultured in vitro with and without various concentrations of germination inhibitors, and the progress of embryogeny was monitored by comparing accumulation of storage proteins in culture with the normal accumulation in seeds. The two major B. napus storage proteins (12S and 1.7S) were purified from seed extracts and analyzed by rocket immunoelectrophoresis (12S protein) or by sodium lauryl sulfate polyacrylamide gel electrophoresis (1.7S protein). During embryo development within seeds both the 12S and 1.7S proteins were first detected when the cotyledons were well developed (embryo dry weight, 0.4 mg), and each storage protein accumulated at an average rate of 26 μg d-1 during maximum deposition. Accumulation of the 1.7S protein stopped when the water content of the embryo began to decline (embryo DW, 2.7 mg), but accumulation of the 12S protein continued until seed maturity (embryo DW, 3.6 mg). At the end of embryo development the 12S and the 1.7S proteins comprised approx. 60 and 20% of the total salt-soluble protein, respectively. When embryos were removed from seeds at day 27, just as storage protein was starting to accumulate, and placed in culture on a basal medium, they precociously germinated within 3d, and incorporation of amino acids into the 12S storage protein dropped from 3% of total incorporation to less than 1%. If 10-6 M abscisic acid (ABA) was included in the medium, amino-acid incorporation into the 12S protein increased from 3% of total incorporation when embryos were placed into culture to 18%, 5d later, and the accumulation rate (27.1±2.6 μg embryo-1 d-1) matched the maximum rate observed in the seed. High osmotica, such as 0.29 M sucrose or mannitol, added to the basal medium, also inhibited precocious germination, but there was a lag period before 12S-protein synthesis rates equaled the rates on ABA media. These results indicate that some factor in the seed environment is necessary for storage-protein synthesis to proceed, and that ABA is a possible candidate.

Seed Size, Life Span, and Germination Date as Coadapted Features of Plant Life History

Abstract: Seed weights vary between species over a range of 10 orders of magnitude, but mean seed weight within species is one of the least plastic components of plant structure (Harper et al. 1970). Seed size appears to be so finely tuned to the ecological life history of species that it is generally conserved at the expense of seed number when environmental conditions necessitate a reduction in the reproductive output of a plant (e.g., Harper and Gajic 1961). Two major studies of seed' weight in relation to environmental conditions have shown shade and drought to be the most important correlates of seed size in the native floras of Britain and California, respectively (Salisbury 1942; Baker 1972). Seed size and lifespan are also correlated in the Californian flora but until now such a correlation has been reported absent from Britain (Salisbury 1942; Hart 1977). I show here that such a correlation does indeed exist when the effect of habitat on seed size is taken into account and I also report the first statistical observation of a positive correlation between seed size and germination date. All dissemules (in some cases actually fruits) are defined as \"seeds,\" following the convention of previous authors (Salisbury 1942; Baker 1972) and to allow comparison with other studies. By confining an analysis of seed size to the flora of a single habitat it is possible to uncover ecological correlates of this variable which would otherwise be masked by the strong effect of habitat differences on seed size. Calcareous grasslands (C. G.) offer a greater number of species for ecological comparison than any other habitat in the British Isles (Ratcliffe 1977). Mean seed weights of 75 dicot species obtained by weighing samples collected from this habitat in southern England (Silvertown 1979) and from published measurements (Salisbury 1942; Grubb 1976) show that biennials and perennials have similar ranges of seed weight while annuals have significantly lighter seeds than longer-lived herbs (Wilcoxon twosample test, P < .01; fig. 1). The low seed weight of annuals, in association with their characteristically greater reproductive effort (Harper 1977) maximizes seed number and opportunities for colonizing gaps in the vegetation by dispersal (Baker 1974; Rabinowitz 1978). Small size also favors the chances of a seed being incorporated in the pool of buried seed (Grime 1979)-an important strategy for persistence in species which have a short lifespan as reproducing individuals (Cohen 1966; Roberts and Feast 1973). The importance of habitat in determining seed size within a group of species of similar life span is emphasized by a comparison of the seed weights of annual arable weeds with the annuals of calcareous grassland in figure 1. The C. G. annuals are significantly lighter than the arable weeds (P < .01; there is no significant difference in seed weights between C. G. biennials, C. G. perennials, and arable annuals). Germination dates for C. G. plants were obtained by direct observation of permanent quadrats during a study of this habitat, and from literature sources

Levels of H+ and other monovalent cations in dormant and germinating spores of Bacillus megaterium.

Abstract: Previous investigators using the extent of uptake of the weak base methylamine to measure internal pH have shown that the pH in the core region of dormant spores of Bacillus megaterium is 6.3 to 6.5. Elevation of the internal pH of spores by 1.6 U had no significant effect on their degree of dormancy or their heat or ultraviolet light resistance. Surprisingly, the rate of methylamine uptake into dormant spores was slow (time for half-maximal uptake, 2.5 h at 24 degrees C). Most of the methylamine taken up by dormant spores was rapidly (time for half-maximal uptake, less than 3 min) released during spore germination as the internal pH of spores rose to approximately 7.5. This rise in internal spore pH took place before dipicolinic acid release, was not abolished by inhibition of energy metabolism, and during germination at pH 8.0 was accompanied by a decrease in the pH of the germination medium. Also accompanying the rise in internal spore pH during germination was the release of greater than 80% of the spores K+ and Na+. The K+ was subsequently reabsorbed in an energy-dependent process. These data indicate (i) that between pH 6.2 and 7.8 internal spore pH has little effect on dormant spore properties, (ii) that there is a strong permeability barrier in dormant spores to movement of charged molecules and small uncharged molecules, and (iii) that extremely early in spore germination this permeability barrier is breached, allowing rapid release of internal monovalent cations (H+, Na+, and K+).

Induction of a light requirement during seed development and its ecological consequences

Abstract: Germination in many arable weeds and herbaceous plants of marshland and heathland depends on exposure of the seed to unfiltered sunlight1–4. In contrast, seeds of many grasses, legumes and woody species exhibit no such requirement and are capable of germination in darkness1–4. These interspecific differences are apparent in seeds immediately after their removal from the parent plant and in theory could be due to major differences in seed physiology. Here we present evidence supporting the alternative hypothesis that the contrasting responses to light are imposed by differences in the light-filtering properties of the maternal tissues which surround the developing seeds.

The establishment of Rhododendron ponticum in the Killarney oakwoods, S. W. Ireland

Abstract: SUMMARY (1) Rhododendron ponticum was introduced into the Killarney area of S.W. Ireland during the 19th century, and has subsequently spread by means of large numbers of very small, easily dispersed seeds, throughout the semi-natural oakwoods (BlechnoQuercetum association). It is now a serious threat to these woods by shading the ground flora and preventing regeneration of native woody species. (2) The woods have been subject to almost continuous human disturbance and to grazing for at least four centuries, and they are currently severely overgrazed by the introduced sika deer (Cervus nippon). This disturbance and grazing is a major factor in aiding the spread of Rhododendron ponticum. (3) Seedlings of R. ponticum are closely associated with bryophyte communities on slopes. Successful germination appears to occur almost exclusively in bryophyte communities of less than 1-cm depth. These 'safe sites' seem to provide the necessary humidity and light for germination, as well as offering some protection from adverse factors.

Germination properties of a spore coat-defective mutant of Bacillus subtilis.

Abstract: The presence of the gerE36 mutation in strains of Bacillus subtilis 168 resulted in poor germination of their spores in a range of germinants, as measured by the fall in absorbance of spore suspensions. Although resistant to heat and organic solvents, spores were sensitive to lysozyme; electron microscopy revealed that their coat structure was incomplete. These spores responded to germinants by losing heat resistance and changing from phase bright to phase gray. The release of dipicolinic acid and the fall in absorbance of spore suspensions reached only 75 and 50% of wild-type levels, respectively, but followed the same time course as the loss of heat resistance. Although the germination response was incomplete, the concentration of L-alanine required to elicit it was the same for the mutant as for the wild type. The properties of mutant spores suggest that an intact spore coat is not required for the initial interaction between germinant and spore, but that the coat layers may contain molecules important in later stages of germination. In transduction with phage SPP1, the gerE36 mutation mapped between citF and ilvB and was 90% cotransduced with citF2. The gerE mutation identifies the location of a gene important for the progress of late stages of spore formation.

How diversified seed-germination behavior is selected

Abstract: The seed populations of many plant species have diversified germination behavior. For example, most weeds and arid-zone ephemerals produce seed crops of which a proportion have innate dormancy. Harper (1977, chap. 3) and Angevine and Chabot (1979) review examples which have been investigated in detail. In many cases one mother produces two seed morphs (\"somatic polymorphism\"), which often have different levels of dormancy. Beyond this, some seeds on a mother may be immediately germinable and others not without there being obvious morphological differences, as in the hard-seededness of legumes. In a few cases dormancy polymorphism has been shown to be genetically controlled, but this is \"probably the exception rather than the rule\" (Harper 1977, p. 69). Cohen's (1966, 1967, 1968) models predicting what proportion of desert annual seeds should germinate in response to rain have been widely cited (MacArthur 1972; Harper 1977; Levin 1978; Jain 1979; Real 1980) as showing what selective forces favor diversified behavior. The models ask what behavior maximizes \"the long-term average . . . of the specific growth rate of the seed population\" (Cohen 1966). If \"population\" is interpreted as a deme, the models are therefore groupselectionist. Alternatively the models can be viewed as predicting the outcome of competition between two or more clonally reproducing populations. Nonmathematical explanations for diversified germination behavior also commonly invoke the perpetuation of the species (e.g., Koller 1969, p. 451; Mayer and Poljakoff-Mayber 1975, p. 152). Here I point out that these group-selectionist assumptions are unnecessary: Diversification of seed behavior could be produced either by selection operating on mother plants, or by frequency dependence in the success of germinated seedlings in producing a seed crop, or by both. I outline how any patterns of diversification produced by frequency dependence should depend on dispersal and on the spatial scale of competition, and indicate what evidence might allow the relative importance of selection on mother plants, and of frequency dependence, to be assessed. I argue that much diversification is produced by selection operating on the mother's fitness. In Cohen's models diversified behavior increases the growth rate of a seed population when there is a risk that any one course of action (in this case, germination) will lead to the mortality of all individuals taking that course. Essentially this is because fitness averages arithmetically over different courses of action which are alternatives, but geometrically over a series of generations (Felsenstein 1976). Any generation in the series which has zero survival will render valueless even the greatest successes in other generations. The fitness of a mother plant is equivalent to the expected growth rate of the population of seeds which are its progeny. Cohen's models therefore predict within-mother di-

Influence of germination date on survival and fecundity in wild lettuce Lactuca serriola

Abstract: Lactuca serriola L. seedlings emerge throughout the year with germination peaks in early winter and late spring. These peaks are followed closely by high levels of mortality which together produce an almost constant plant density. Plants from seeds which germinate in the winter months produce more seeds than those which germinate in spring and summer and this is considered to be associated with the duration of the rosette stage. However, the increased fecundity of the former is partially annulled by their higher mortality. It is concluded that the winter-germinated plants are the main seed producers while those which germinate in spring and summer may act as insurance against complete loss of the more fecund individuals.

Low temperature effect on selective fertilization by pollen mixtures of wild and cultivated tomato species

Abstract: In vitro pollen germination of cultivated tomato, Lycopersicon esculentum Mill., is inhibited by an ambient temperature of 5°C, more so than pollen from a Peruvian ecotype of Lycopersicon hirsutum Humb. & Bonpl. originating from an altitude of 3200 m. The frequency of L. hirsutum gametes contributing to hybrid zygote formation is more than doubled when controlled fertilizations with pollen mixtures of the two species occurs at 12/6°C as compared to crosses with the same mixtures at 24/19°C. The results suggest that differential selection at the gametophytic level occurs in response to low temperature regimes. To our knowledge this is the first time in higher plants that alteration of an environmental factor has been demonstrated to change selection values of male gametophytes in a fashion predicted by the ecology of the parental sporophytes.

Shoot Histogenesis in Cotyledon Explants of Radiata Pine

Abstract: The histological events associated with shoot primordium formation in cultured excised cotyledons from germinated seed of radiata pine (Pinus radiata D. Don) were examined. Cytological changes in the explants were observed by day 1 in culture. Mitotic activity, initially random, became restricted to the epidermal and subepidermal cell layers closest to the medium. This led to the formation of meristematic tissue along the entire length of the cotyledon during the first 3 wk in culture. Within this meristematic zone, meristemoids, shoot primordia, and finally shoots with well-developed apical meristems, needles, and needle primordia were formed.

Analysis of how ant behaviors affect germination in a tropical myrmecochore Calathea microcephala (P. & E.) Koernicke (Marantaceae): Microsite selection and aril removal by neotropical ants, Odontomachus, Pachycondyla, and Solenopsis (Formicidae).

Abstract: The evolutionary effects of a tropical ant-seed interaction are examined by posing questions about the fate of Calathea seeds carried by neotropical ants. Where do ants take seeds and what do they do with them? How do ant behaviors affect seed germination? Treatment of seeds by ants is determined by a series of seed-fate trials in captive colonies. There is no evidence of seed predation by ants. Odontomachus laticeps, Pachycondyla spp, and Solenopsis geminata rapidly displace seeds to ant nests, determine the microsites of seeds, and remove the seed arils for food. The seed arils are rich in lipids. The effects on germination of microsite selection and aril removal are quantitatively evaluated. Seeds which are immediately taken to a consistently moist spot germinate readily; 72% germinate, with a mean germination speed of 29 days. For such seeds aril removal does not significantly affect germination. In contrast, seeds which experience a delay before encountering appropriate germination conditions seem to exhibit an induced dormancy (sensu, Harper 1977) and a lower germination percentage. They take longer to germinate (up to 85 days) even after conditions become appropriate. It appears that their germination is enhanced by aril removal, which may act as an environmental cue to break dormancy. Such a mechanism would indicate that ant-handling of seeds is predictive of favorable conditions for seedling growth and establishment. The exact nature of such conditions and the effects on plant population dynamics remain to be seen.

Observations on the survival and germination of resting spores of three chaetoceros (bacillariophyceae) species1,2

Abstract: Resting spores (hypnospores) of Chaetoceros diadema (Ehrenberg) Gran, Chaetoceros vanheurckii Gran, and Chaetoceros didymus Ehrenberg were collected from a large plastic enclosure moored in Saanich Inlet, B.C., Canada. The effects of combinations of temperature and irradiance on the germination of these resting spores were investigated. Nutrient uptake, carbon fixation, and changes in the photosynthetic capacity of the germinating spores were also examined. Resting spores germinated optimally at combinations of temperature and irradiance similar to those in the environment during sporulation. They did not germinate at irradiances 1.3 μEin m−2 s−1 or temperatures >25.3° C. Nitrate, phosphate and silicate were taken up after the resting spores had germinated and resumed vegetative growth. Chlorophyll a fluorescence in vivo, and the DCMU-induced increase in in vivo fluorescence also increased after the resting spores had germinated. Resting spores began to fix carbon as soon as they were placed in light. Spores remained viable for at least 645 d. The length of time between first exposure to light and germination did not change during this period; however, the percentage of viable resting spores decreased markedly. None of the Chaetoceros spores germinated after 737 d of storage at 2–4° C in darkness.

Germinable seeds and periodicity of germination in annual grasslands

Abstract: Germinable seed reserves and periodicity of germination of the plant species in annual communities were periodically and intensively sampled from 1974 through 1977 at the Sierra Foothill Range Field Station (SFRFS) and the U.S. Forest Service’s San Joaquin Experimental Range (SJER). One hundred samples of surface soil with accompanying litter were taken every 8 weeks, except when they were taken 1, 3, and 5 weeks after annual initial rains. Few germinable seeds (mostly exotic annual legumes at SFRFS) were carried over from year to year. Dominant annual grasses had virtually no annual carryover. Litterborne and soilborne seed reserves gradually increased as the current year’s crop was dispersed. Through the fall, each species exhibited its own pattern of increased germ inability, which was highly dependent on its inherent afterripening requirements. In years when the initial fall rains resulted in simultaneous germination, the flush of germination began within a week, and by 5 weeks the reserve of germinable seeds was largely exhausted. The seedlings that established in these years accounted for only 20 to 30% of the germinable seeds present in the litter and surface soil before the initial rain. When the communities were subjected to 2 years of extreme drought (1975-76 and 1976-77), established seedling density and subsequent seed reserves dropped dramatically; species composition, however, remained relatively stable. Near-normal moisture conditions in 1977-78 resulted in near-normal communities except that a higher percentage of the seed reserve became established plants than before the drought.

Gigaspora Gigantea: Observations on Spore Germination of a Va-Mycorrhizal Fungus

Abstract: Spore germination of a vesicular-arbuscular mycorrhizal fungus in the absence of a host plant was investigated. Spores of Gigaspora gigantea were tested for the ability to germinate under laborator...

Variation in seed germination inhibition of Chenopodium bonus-henricus in relation to altitude of plant growth

Abstract: Chenopodium bonus-henricus achenes have poor germination whatever the temperature; this phenomenon is reinforced with increasing elevation of seed harvest. Since the excised embryo is never dormant, germination of intact seeds is prevented by the seed coat. The seed coat thickens and contains more polyphenols with increasing elevation. This process appears to be responsible for the reduced permeability of the seed coat. High germination temperatures reduce the gas solubility in water and, at the same time, increase polyphenol oxidation in the seed coat. The embryos of seeds collected at low elevation thus receive a reduced O2 flux. When high temperature is applied to seeds from high elevation, the O2 flux is drastically reduced because of the thicker seed coat and increased levels of oxidizable polyphenols.There is a high correlation between germination and the mean of the average daily temperature for the 30 days preceding harvest, high temperature prior to harvest being correlated with high germination....

Development and enzymatic changes during pollen development in boron deficient maize plants

Abstract: Maize (Zea mays L.) plants subjected to severe deficiency of boron (0.0026 ppm B) failed to produce tassels with functional flowers. In plants subjected to moderate deficiency of boron (0.013 ppm B), emergence of tassels and anthesis was suppressed and delayed. In a large percentage of boron deficient plants the stamens lacked sporogenous tissue and appeared as staminodes or floral appendages that either lacked or had branched vascular supply. The apparently normal stamens of these plants also failed to dehisce and showed a marked decrease in pollen producing capacity, pollen size and pollen germination. Even in plants that were only marginally deficient in boron (0.066 ppm B), without any foliar symptoms of boron deficiency, pollen grains showed poor germination and changes in enzyme activities. Pollen grains of such plants had low activities of catalase, acid phosphatase, starch phosphorylase and invertase and high activities of ribonuclease and amylase.

The Effect of Sodium and Chloride Salts on the Germination of Gigaspora Margarita

Abstract: At various Na+ and Cl- concentrations, germination rates of azygospores of Gigaspora margarita were reduced more in the presence of Cl- than Na+. Viable spores, which had not germinated after 12 da...

The microbial origin of the allelopathic potential of Adenostoma fasciculatum H & A.

Abstract: The release of phytotoxic compounds has been proposed to be involved in the inhibition of seed germination under the canopy of Adenostoma fasciculatum (McPherson and Muller 1969). McPherson et al. (1971) tentatively identified the phytotoxins as phenolic compounds; however, the soil extraction data presented in this study indicate that insufficient quantities of available phenolics are present in the soil to account for the lack of growth observed in the field. Soil from burned and unburned Adenostoma—dominated sites were exchanged and planted with herb seeds. While toxicity developed in soil from the unburned site, the resulting pattern of germination suggested that the toxicity originated from the soil and not from the shrub canopy. Treatments to disrupt the metabolism of soil microbes, and to isolate selectively the microbial fraction from the soil, as well as other experiments, lead to the conclusion that the soil toxicity was the result of phytotoxins of microbial origin. It is suggested that the role of Adenostoma in the suppression of herb growth may lie in its association with soil microbes that produce and release substances capable of inhibiting the germination and growth of plants.

Seed dormancy in Rumex species in response to environmental factors

Abstract: . Many Rumex species show similar seed dormancy characteristics but there is more information concerning R. crispus and R. obtusifolius than other species. These species respond positively to red or white light. Far-red light applied for short periods may promote or inhibit germination depending on the timing of the irradiation in relation to temperature change; but long periods of far-red inhibit germination. Seeds may also be stimulated to germinate in the dark by low-temperature stratification at 15°C or less providing the temperature of the seeds is subsequently raised to a minimum of about 15°C. Seeds can, however, germinate at lower temperatures providing they have received other appropriate stimulatory treatment. Seeds also respond to alternating temperatures. In a diurnal cycle the minimum upper temperature required is about 15°C and the maximum lower temperature is about 25°C. The optimum period spent at the upper temperature is about 8 h when it is 15–25°C but the optimum period decreases as the upper temperature is increased above this range so that at 45°C, for example, it is only about 30 min. The period spent at the lower temperature in a diurnal cycle is not critical. Providing these criteria are met, the percentage germination increases with the number and amplitude of the cycles. The warming part of the cycle is necessary for the response but so far there is no convincing evidence that cooling itself is important. Secondary dormancy is induced at constant temperatures at a rate dependent on temperature, but apparently only in the presence of oxygen. This feature affects the optimum timing of a temperature change or exposure to light. Strong positive interactions are shown between stimulatory temperature treatments and white or red light. Unlike many other weed species the seeds respond only slightly to nitrate ions. The implications of these responses are discussed in relation to field behaviour.

Patterns of change in dormancy during burial of seeds in soil

Abstract: Changes in dormancy during burial in soil were recorded over a period of two years for seeds of Polygonum persicaria. Senecio vulgaris, Sisymbrium officinale, Chenopodium bonus-henricus and C. album. Dormancy levels were deduced from germination tests on exhumed seeds under standard conditions in light or darkness. Decreases and increases in dormancy were in most species part of a seasonal cycle, that was repeated in the second year, except for C. bonus-henricus. Both Chenopodium species showed profound differences in the dependency of light for germination during the seasons. C. album showed some characteristics of winter annuals, whereas the other four species behaved like summer annuals. Temperature, nitrate and soil moisture were among the factors that modified dormancy in soil.

Seed Dormancy in Red Rice (Oryza sativa) I. Effect of Temperature on Dry-Afterripening

Abstract: The effect of postharvest storage temperature (-15, 5, 20, and 30 C) on seed dormancy of red rice (Oryza sativa L. 'strawhulled (SH)'Y, an annual species, was studied. Intact and dehulled (by hand) seeds were dormant at harvest. Intact seeds were nondormant (greater than 90% germination at 30 C) after dry storage at 20 or 30 C for 4 weeks after harvest. In intact seeds stored dry at 5 C, the degree of dormancy was dependent upon postharvest exposure time at 20 C prior to storage. Dormancy of intact seeds decreased at 5 C as this initial postharvest exposure to 20 C was increased from 2 to 7 days. This effect of initial 20 C exposure was independent of seed moisture content (11 to 12%). After dry storage of intact seeds at 5 C, dehulling promoted germination. Germination of such dehulled seeds increased with increasing storage time at 5 C up to 11 months when complete germination occurred. The response of seeds dehulled immediately after dry storage at 5 C was independent of prior exposure time (2 to 7 days) at 20 C. Storage at -15 C prevented all forms of dry- afterripening for 1 yr. Additional index words. Germination.

Seed production and spring seedling establishment of diffuse and spotted knapweed.

Abstract: Annual seed production of diffuse (Centurea diffusa) and spotted knapweed (Centurea maculosa) is reduced in dry years by a reduction in the number of viable seeds per seed head and increases when above-normal precipitation occurs by increase in the number of heads/flower stem. Seed production was approximately l,OOOfold that needed to maintain observed levels of infestation. Seedlings emerging in April had a high rate of survival with most plants flowering the following season, while those emerging after May 15 had a very low survival rate and almost no flower stem production the following season. (Table 1). Each site was sampled annually the first week of August in 1973 through 1976. The number of flower stems per unit area was estimated by random counts of m* hoop. Each area was subsampled to determine the number of seed heads/flower stem and the number of mature achenes/flower head. Only seed heads that were in the maturity range of well-developed seed, but had bracts still tightly closed, were counted for the latter measurement. Location and general features of each site are shown in Table 1. Diffuse and spotted knapweed are short-lived perennials of the Centaurea genus that have become major weed problems on semiarid range and pasture lands of the Pacific Northwest. The problem of these weeds, which are continuing to spread into many prime grazing areas, was recently reviewed (Maddox 1979). Control of these species is possible by chemical means (Renney and Hughes 1969) but these measures are not always practical because of economics, terrain, or environmental considerations. Several biotic agents are under study [Maddox (1979); Watson and Renney (1974,] but at present have only a minor impact. Watson and Renney (1974) summarized observations related to the reproduction of these species. In general, they reported that these species under range conditions were capable of producing 400-900 seeds/plant that would germinate under a range of temperatures of 7 to 34O C when optimum moisture was supplied. Some post harvest and light-induced dormancy was measured. We have also observed viability greater than 80% of the seeds still retained in the seed heads of diffuse in April. These normally are fully dispersed by mid June. Both fall and spring seedling emergence is common with these species.

Seed production and longevity, seasonal emergence and phenology of wild radish (Raphanus raphanistrum L.).

Abstract: Experiments conducted from 1977 to 1979, at Rutherglen, north-eastern Victoria, investigated seed production, seed longevity, seasonal emergence and phenological development in wild radish (Raphanus raphanistrum L.), a weed of field crops. Seed production of wild radish reached 17 275 seeds/m2; seeds retained viability and germinated over a period of three years. The loss of viability was faster at the soil surface or at 1 cm depth than at 5 or 10 cm. Of 1000 wild radish seeds buried at 1 cm depth, 737 emerged after three years, compared with 367, 167 and 5 at 0.5 and 10 cm, respectively. Phenological development of wild radish was affected by time of planting, and the duration of the period from plant emergence to plant senescence ranged from 5 to 10 months. Temperature appeared to influence development up to flowering, but photoperiod affected the length of flowering. Plants emerging at any time during the year were able to flower and seed successfully. The implications of these findings for control programs are discussed.

Seed Germination of North American Orchids. I. Native California and Related Species of Calypso, Epipactis, Goodyera, Piperia, and Platanthera

Abstract: Seeds of native California and related orchids were germinated in vitro on five basal media and 43 modifications. Germination periods extended from several weeks to almost 2 yr. Seeds from immature capsules germinated faster and in higher proportions than those from mature fruits. The most suitable media for orchid germination are those devised for the culture of barley embryos (Norstog) and a modified Curtis medium containing urea and calcium carbonate instead of ammonium nitrate and calcium nitrate.

Digestive Seed Predation by a Costa Rican Baird's Tapir

Abstract: The large ungerminated seeds of guanacaste (Enterolobium cyclocarpum) and carao trees (Cassia grandis), and plastic buttons, were fed to a captive adult male Costa Rican Baird's tapir (Tapirus bairdi) in artificial fruits. Seed survival during gastrointestinal passage and seed passage rate was studied. The tapir's digestive processes killed 78 percent of the guanacaste seeds and all of the carao seeds, despite their hard seed coats, apparently because they germinated and thereby become suspectible to digestive fluids. Guanacaste seeds that survived required an average of 15.3 days to make the trip through the tapir; the dead carao seeds required an average of 10.3 days and the two sizes of buttons required an average of 8.1 days (730 mg) and 10.3 days (360 mg) to make the passage. The tapir is clearly a seed predator of guanacaste seeds as well as a potential dispersal agent. Which of these functions is more important depends on the unknown behavioral interaction between the tree and the tapir. VERTEBRATE SEED PREDATORS KILL SEEDS by chipping them with a beak or incisors, breaking and grinding them with molars or a gizzard, and by direct chemical digestion. Very hard seeds and nuts, and especially legume seeds, are generally viewed as immune to chemical digestion. Hard seeds and nuts which are dispersed by complete passage through the digestive tract are often encountered in the dung of large herbivorous mammals. It is commonplace to assume that the number found in the dung approxi-mate the number of intact seeds that were swallowed. This assumption may be reasonable for certain species of seeds and animals, but here I show that it is not valid for Baird's tapir (Tapirus bairdi) and the large hard seeds of two legumes, guanacaste (Enterolobium cyclocarpum) and carao (Cassia grandis). MATERIALS AND METHODS I used the captive adult male Baird's tapir at Finca La Pacifica (7 km north of Caiias, Guanacaste Province, Costa Rica) for experiments. Born in late 1970 and acquired by Finca La Pacifica a few months later, it ranged free around the ranch house, eating milk, table scraps, and wild vegetation. At about two years of age, it was placed in a wood-fenced corral approximately 20 by 20 m in area. It was seven years old at the time of the experiments and suffered only occasional indispositions with tick infestations and foot fungal attacks, both of which were cleared up by treating with the chemicals used to cure horses and cows of the same diseases. It seemed well adjusted to corral life and did not display pacing or other behaviors associated with neurotic caged animals. Its diet, on which it appeared quite healthy, was kitchen refuse, table scraps, and copious supplies of weedy vegetation offered twice a day. It took food readily from the hand and was an eager participant in the feeding experiments described here which were conducted in the same period as were choice tests with foliage (Janzen 1981a); the regular diet was therefore supplemented with a greater species richness of foliage than usual, but not greater bulk or roughage. I have found that wild Baird's tapirs in Santa Rosa National Park (northwestern Guanacaste) defecate in water wherever possible, and the captive tapir did the same (and see Young 1906). The stream that flowed through its corral was diverted into a concrete-lined pool 20-40 cm deep with a plugged drain. Dung floated in the pool for a short time and then disintegrated through soaking and trampling. The seeds and buttons used in the experiments are all denser than water, with the result that they collected in the pool bottom. Once a day the plug was pulled and the pool contents passed through a 3 mm mesh screen that removed all particles large enough to be a button or seed fragment. The particular species of seeds used in the experiments (fig. 1) were chosen because 1) they were large enough to locate easily after passage through the animal but small enough to be swallowed readily, 2) they were hard enough to escape digestion, 3) one seed type (guanacaste) is found in livestock dung and is believed to have been dispersed this way by Pleistocene mammals (Janzen and Martin 1981), and 4) they are potentially dispersed by tapirs in the wild since the captive tapir, would eat the fruit of both species and both species occur in tapir habitat. The guanacaste seeds (Enterolobium cyclocarpum) weighed between 450 and 650 mg (specific gravity 1.34) and came from a single crop collected in March 1977 from below tree number 34 in Santa Rosa National Park. They were shelled by hand out of naturally fallen mature fruits and not touched by REPRODUCTIVE BOTANY 59-63 1981 59 This content downloaded from 157.55.39.153 on Mon, 19 Sep 2016 05:10:34 UTC All use subject to http://about.jstor.org/terms metal objects. When a sample of 300 living seeds was placed in water, 3 percent germinated immediately, and the remainder did not take up water for at least two months. When a subset of 100 of the ungerminated seeds was notched with a file and placed in water, all germinated within two days. Guanacaste seeds are hard and smooth and require about 70-200 kg direct pressure to break, depending on the angle of attack (Janzen and Higgins 1979). The carao seeds (Cassia grandis) were similar in weight, shape, texture, and appearance to the guanacaste seeds (fig. la and Janzen 1977) and were hand-shelled out of freshly fallen mature pods from the tree growing by the carpenter's shop at Finca La Pacifica. When a sample of 100 seeds was placed in water for two months, none germinated. After these seeds were notched with a file, all germinated within two days in water. 60 Janzen If guanacaste fruits were offered to the tapir, it chewed them thoroughly and spat out a variable percent of the seeds, swallowed others, and broke or scarified a few. It would not chew up entire carao fruit in its well-fed state. Therefore, to examine the fate of the seeds in a maximally controlled manner, I used artificial fruits to entice the tapir to swallow large numbers of seeds in one meal. Unpeeled ripe bananas were cut into 3 cm sections, and two seeds (or buttons, see below) were inserted in a slit in the pulp of each section (fig. Id). Since ripe banana was a favorite food of the tapir, the seeds were always swallowed (though an increase in seed numbers per 'fruit' resulted in seed spitting, Janzen 1981b). Rarely, the seeds were chewed lightly before swallowing, and, on five occasions, a guanacaste seed was broken. When a seed was broken, the break made a very loud noise, and these seeds were not counted in the tabulations reported here. The volume of seeds and buttons fed, about 200 cc, is a trivial portion of the daily diet of the tapir. There is no reason to believe that the seed-passage rate was influenced by the contents of the artificial fruits. It ate several kilos of bananas almost every meal, and the seeds were immediately separated from the slippery banana pulp by tongue, palate, and throat action. The seeds were collected from dung until no more seeds appeared for at least four days. In order to know if seeds which never reappeared had been digested or were simply delayed in passage, I also fed the tapir indigestible white plastic buttons along with the seeds. Some were broken in chewing, but all fragments of a quarter of a button or better were recovered from the dung. When a button broke, it could be heard distinctly. The particular buttons were chosen because their shape and size were similar to those of the seeds (fig. lc). They weighed 360 or 730 mg and had a specific gravity of 1.75. These experiments cannot be repeated exactly because the tapir died of a respiratory disease in August

Interaction of light and temperature on the germination of Rumex obtusifolius L.

Abstract: Germination of Rumex obtusifolius L. seeds (nutlets) is low in darkness at 25° C. Germination is stimulated by exposure to 10 min red light (R) and also by a 10-min elevation of temperature to 35° C. A 10-min exposure to far-red light (FR) can reverse the effect of both R (indicating phytochrome control) and 35° C treatment. Fluence-response curves for this reversal of the effect of R and 35° C treatments are quantitatively identical. Treatment for 10 min with light of wavelenght 680, 700, 710 and 730 nm, after R and 35° C treatment, demonstrates that germination induced by 35° C treatment results from increased sensitivity to a pre-existing, active, far-red-absorbing form of phytochrome (Pfr) in the seeds.