Non-deep simple morphophysiological dormancy in seeds of the weedy facultative winter annual Papaver rhoeas

Embryos in freshly matured seeds of the facultative winter annual Papaver rhoeas are underdeveloped and physiologically dormant; thus, seeds have morphophysiological dormancy (MPD). Seeds lost physiological dormancy during 12 weeks of burial in moist soil at 12 h/12 h daily alternating temperature regimes of 15/5°C, 20/10 °C and 25/15 °C but not at 1 °C. Physiological dormancy was not broken in seeds stored dry at room temperature for 12 weeks. After physiological dormancy was broken, seeds required light for embryo growth (i.e. for loss of morphological dormancy) and consequently for germination. After a 12-week period of burial in soil at 25/15 °C, seeds that matured in 1997 germinated to 100% in light at 25/15 °C, demonstrating that cold stragification temperatures (≈ 0.5–10 °C) are not required for embryo growth. Thus, seeds have non-deep simple MPD. During exposure to low winter temperatures (5/1 °C, 1 °C), 52% of the seeds with physiologically non-dormant embryos entered conditional dormancy and thus lost the ability to germinate at 25/15 °C but not at 15/5 °C or 20/10 °C. The peak of germination for seeds sown in southern Sweden was in autumn, but some also germinated in spring. A higher percentage of seeds that matured in a relatively warm, dry year (1997) came out of MPD and germinated than did those that matured in a relatively cool, wet year (1998) at the same site.     

Seasonal changes in the germination of buried seeds of Monochoria vaginalis

This study investigates the seasonal variation of germination ability of buried seeds of Monochoria vaginalis (Burm.f.) Presl var. plantaginea Solms. The field-collected seeds were buried in a flooded or an upland field and then exhumed monthly. The exhumed seeds were germinated under four temperature regimes. The seeds exhumed from the flooded soil were dormant at the beginning of burial and proceeded into a conditional dormancy/non-dormancy/conditional dormancy cycle throughout the remaining period of the experiment. The seeds exhumed monthly from the non-flooded soil exhibited an annual dormant cycle, which is dormancy/conditional dormancy/non-dormancy/conditional dormancy/dormancy. At day and night temperatures of 25/20 °C, the exhumed seeds from both the flooded and the upland soil resembled each other in terms of seasonal variation of the germination percentage. In September and October, more seeds exhumed from upland soil failed to germinate under higher temperature than from flooded soil. Strictly avoiding exposure to light during seed exhuming and seed testing prevented the seeds from germinating. A short exposure of the exhumed seeds to light during preparation promoted dark germination when the seeds were at the non-dormant stage. The potential implications of our results for weed management strategies in rice production are discussed.     

Seasonal changes in germination responses of buried seeds of the weedy summer annual grass Setaria glauca

Seeds of Setaria glauca (L.) Beauv. buried in soil and exposed to natural temperature cycles exhibited seasonal changes in temperature, but generally not light; dark requirements for germination. Seeds were dormant at maturity in late September and October (autumn), and during burial from October to January they entered conditional dormancy, germinating up to ≥60% in light and darkness at daily thermoperiods of 25/15,30/15 and 35/20^C by January. During burial from February to May or June, seeds became non-dormant and germinated up to 68–100% in light and darkness at 15/6,20/10,25/15,30/15 and 35/20^C in May or June. At maximum yearly temperatures in June or July–August, 65–89% of the seeds entered conditional dormancy (germinating at 30/15 and 35/20, but not at 15/6,20/10 and 25/15^C), and the others entered dormancy (not germinating at any thermoperiod). Thus, most buried seeds had an annual conditional dormancy/non-dormancy cycle, but some had an annual dormancy/non-dormancy cycle. Except for seeds buried in 1990 that lost the ability to germinate in darkness at all thermoperiods the first summer of burial, seeds incubated in light and in darkness exhibited the same patterns of seasonal changes in germination responses. Although conditionally dormant and non-dormant seeds germinated to high percentages in darkness in Petri dishes, seedlings were found only in bags of seeds exhumed in April and May 1983, indicating that some factor(s) associated with the burial environment other than darkness prevented germination of buried seeds.     

Germination, emergence, and dormancy of Mimosa pudica

Mimosa pudica (common sensitive plant) is a problematic weed in many crops in tropical countries. Eight experiments were conducted to determine the effects of light, seed scarification, temperature, salt and osmotic stress, pH, burial depth, and rice residue on the germination, seedling emergence, and dormancy of M. pudica seeds. Scarification released the seeds from dormancy and stimulated germination, though the germination of the scarified seeds was not influenced by light. The scarification results indicate that a hard seed coat is the primary mechanism that restricts germination. The germination increased markedly with the exposure to high temperature "pretreatment" (e.g. 150°C), which was achieved by placing non-scarified seeds in an oven for 5 min followed by incubation at 35/25°C day/night temperatures for 14 days. The germination of the scarified seeds was tolerant of salt and osmotic stress, as some seeds germinated even at 250 mmol L⁻¹ NaCl (23%) and at an osmotic potential of −0.8 MPa (5%). The germination of the scarified seeds was >74% over a pH range of 5–10. The seedling emergence of the scarified seeds was 73–88% at depths of 0–2 cm and it gradually decreased with an increasing depth, with no seedling emergence at the 8 cm depth. The rice residue applied to the soil surface at rates of ≤6 t ha⁻¹ did not influence the seedling emergence and dry weight. The information gained from this study identifies some of the factors that facilitate M. pudica becoming a widespread weed in the humid tropics and might help in developing components of integrated weed management practises to control this weed.     

Annual cycles of germinability and differences between primary and secondary dormancy in buried seeds of Echinochloa crus-galli

The seasonal changes in percentage of dormant seeds of Echinochloa crus-galli in the field were recorded for 4 years. The lots of seeds were wrapped in nylon fabric, buried 20 cm under the grass sward and exhumed at monthly intervals. The proportion of seeds germinating under light conditions at a constant temperature of 25 °C fluctuated between 0% and 96%, with maxima in May–July and minima in September–November. Small between-year differences in the course of summer dormancy induction and its winter termination were probably caused by variation of weather conditions.
Attributes of dormancy innate to seeds after maturation (primary dormancy) and dormancy induced in buried seeds during the summer (secondary dormancy) were compared by investigating the rate of dormancy termination during storage of (a) dry seeds at 25 °C, (b) imbibed seeds at 5°C and (c) in seeds buried under field conditions during October–June. Percentage of germination increased faster in secondary than primary dormant seeds at both constant 25 °C and 5 °C. The seeds with primary and secondary dormancy also differed in the response to `germination pre-treatment', a 10-day exposure of imbibed seeds at 25 °C that causes germination of the non-dormant fraction of seed materials. After this treatment the time to resuming germination in primary dormant seeds was substantially increased, whereas the secondary dormant seeds were much less affected. Annual variation in the proportion of germinable seeds explains the low efficiency of autumn soil cultivation for decreasing reserves of E. crus-galli seeds in the soil.     

Behaviour of buried and surface-sown seeds of Parthenium hysterophorus

Parthenium hysterophorus L. seeds were buried at a depth of 5 cm for periods of 2–24 months to determine their longevity. The majority (73.7%) of these seeds were still viable after 24 months of burial. The remainder could not be recovered (18.0%) or were no longer viable (8.3%). There was a log-linear decline in persistence of germinable seeds over time, which indicated a constant rate of loss and a half-life of about 6 years. Seedling emergence from surface-sown seeds was also studied. Although there was considerable rainfall (31 mm), seedlings did not emerge during the first month of this experiment. In the succeeding 3 months, there was substantial seedling emergence after rainfall, and 51.4% of seeds had germinated by the end of the fourth month. After 5 months had passed, further seedling emergence was not detected, and intact seeds could not be located. These findings suggest that seed incorporation into the soil is important to the long-term persistence of P . hysterophorus seeds. In an initial test of germination, unburied seeds from the same seed lot exhibited a degree of innate dormancy, and this may explain the delayed germination observed in the surface-sown seeds. In the seed burial and recovery experiment, innate dormancy was lost after 2 months of burial in the field, although in situ germination of buried seed remained low for at least 24 months. Therefore, it appears that more than one dormancy mechanism may contribute to the persistence of P. hysterophorus seeds.     

Changes in germinability, dormancy and viability of Amaranthus retroflexus as affected by depth and duration of burial

Changes in dormancy and viability of Amaranthus retroflexus seeds were examined after placement in pots that were buried in the field. Seeds were placed in woven nylon envelopes on the soil surface or buried at depths of 2.5, 5 or 10 cm. After 1, 3, 6, 9 and 12 months seeds were exhumed and their germinability was tested to assess changes in dormancy and viability. Depletion of seed stocks placed on the soil surface was partly because of in situ germination that did not exceed 21% and did not vary significantly over the 12-month study period. Less germination of buried seeds occurred in situ , and seeds that did not germinate appeared to acquire dormancy. Exhumed seeds germinated readily; germinability was linearly related to the depth of burial, with those retrieved from the surface germinating least. Cyclical changes in germinability occurred during the 12-month burial period, but this influence was identical for seeds buried at all depths. Germinability was greatest after periods with the lowest mean monthly temperatures and least during the hottest periods. The stimulation of remaining ungerminated seeds exhumed at each period, by the addition of ethephon to the germination medium, provided further evidence of a seasonal acquisition of dormancy, and it was concluded that other unknown factors besides cyclical changes in seasonal temperature were responsible. Irrespective of placement, all seeds lost viability at an exponential rate over time. However, the decline was most rapid for those placed on the surface, whereas the loss in viability became less with increased depth of burial. Possible explanations for this adaptation of enhanced survival when buried are discussed.     

Invasiveness evaluation of fireweed (Crassocephalum crepidioides) based on its seed germination features

In China, fireweed ( Crassocephalum crepioides ) is listed as an invasive plant that is also cultivated as a vegetable. To gain a clearer understanding of its invasiveness and rapid spread, we evaluated its seed dispersal ability, and the influences of light, temperature, pH, NaCl stress, moisture content, and storage periods on its seed germination. Its seed dispersal ability is limited. The seed germination of fireweed is inhibited by darkness, temperatures <10°C or >35°C, and a NaCl solution with a concentration >0.15 mol L⁻¹. The optimal conditions under which nearly all the seeds could germinate are light, with temperatures from 20 to 30°C, and a neutral soil with 40% moisture content. The seeds of fireweed have no apparent dormancy and retain a high viability after room storage for 10 months. Fireweed only has a moderate invasive capacity and its wide distribution in China possibly correlates with its cultivation.     

Variation in the development of secondary dormancy in oilseed rape genotypes under conditions of stress

Summary A substantial amount of seed is left in the fields before and during harvest of oilseed rape. Although this crop exhibits little or no primary dormancy, the absence of certain environmental cues that promote germination of imbibed seeds induces secondary dormancy. The work reported investigated the extent to which environmental stress conditions, including osmotic stress, low oxygen stress and anaerobiosis, induce secondary dormancy in oilseed rape, and examined the variation in development of secondary dormancy between and within genotypes. Osmotic stress was most effective in inducing dormancy. Anaerobic treatment produced very few dormant seeds, as did an atmosphere low in oxygen and high in nitrogen. The development of secondary dormancy under osmotic stress varied considerably between and within genotypes. Dormancy ranged from almost zero to about 60% for winter genotypes and about 85% for spring types. Within genotypes, variations occurred between seed lots and years of harvest. Temperature variations affected the percentage of dormant seeds. More dormant seeds were likely to be produced with incubation under water stress at 20 °C than at 12 °C. In winter genotypes, fewer dormant seeds were produced when incubation temperature and germination test temperatures differed. Thus, incubating at 20 °C and 12 °C, followed by germination tests at 20 °C and 12 °C, respectively, produced most dormant seeds. Also, in the winter genotypes, the potential development of secondary dormancy was positively correlated with the pattern and speed of germination of untreated seeds.     

Germination characteristics of Amaranthus quitensis as affected by seed production date and duration of burial

Thermal requirements for the germination of Amaranthus quitensis, a common annual weed in Argentina, were studied. In addition, temporal changes in dormancy from seeds produced at different times during the growing season were examined. For this second objective, thermal and light requirements for germination were tested in seeds buried at different depths, with or without crop residues. Base and optimum temperatures for germination rates were 12.8°C and 37°C respectively. At dispersal time, maximum percentage germination was 60–70% and this was generally recorded at 35°C/25°C in a 14-h photoperiod. Seed germination tended to increase in later seed collection dates. Seeds of A. quitensis showed seasonal changes in germinability in the soil. In winter, germination of retrieved seeds increased to over 90% until summer, after which there was a decrease until the following winter when germination was close to 40%. There were no differences in germinability between burial depths and crop residue levels. Germination requirements for alternating temperatures and light tended to disappear after burial. Initial viability was 99% and declined slightly during burial. Soil temperature seems to play a crucial role not only by regulating seasonal changes in dormancy, but also by defining the percentage and the germination rate in non-dormant seeds.     

Seed dormancy dynamics and germination characteristics of Solanum nigrum

Four experiments were conducted to study seed dormancy and germination requirements in Solanum nigrum . In Expt 1, seeds were stratified at different constant and stepwise rising temperatures and their germinability was tested at three germination regimes at weekly intervals. In Expts 2–4, seeds dry stored at 4°C and stratified at 5 and 15°C were tested at constant temperatures, as well as fluctuating temperatures with constant and increasing amplitudes. Results suggest that the rate of dormancy release increased with increasing temperatures ranging from 4.5 to 18.6°C. However, prolonged stratification at higher temperatures caused subsequent induction of dormancy. When tested at constant temperatures, stratified seeds germinated between 18 and 34°C, with the optimum between 26 and 30°C, while dry-stored seeds showed no germination. Fluctuating temperatures, with amplitudes ranging from 5 to 15°C, promoted germination of seeds from all treatments. The dormancy dynamics and germination characteristics of the species will have implications for its survival and establishment. This information can be used to predict time of emergence and, thus, improve control of the species in weed management systems.     

Role of temperature in regulating timing of germination in soil seed reserves of Thlaspi arvense L.

Summary. Most freshly-matured seeds of Thlaspi arvense L. (Brassicaceae) were dormant at maturity in May. Seeds sown on soil germinated in autumn and spring, but mostly in autumn. Buried seeds exhumed at monthly intervals and tested in light and darkness over a range of thermoperiods exhibited annual dormancy/non-dormancy cycles. However, the dormant period was short, usually only in April, but sometimes May, and in some years 1–6% of the seeds remained conditionally dormant. After-ripening occurred during summer, and seeds were non-dormant during autumn. Seeds entered conditional dormancy in winter and dormancy in late winter or early spring. When buried dormant seeds were kept at 25/15, 30/15 or 35/20°C for 12 weeks, they gained the ability to germinate to 95–100% at 15/6, 20/10, 25/15, 30/15 and 35/20°C. After burial for 12 weeks at 15/6 and 20/10°C, seeds germinated to 80–100% at 15/6, 20/10 and 25/15°C. but to only 11–64% at 30/15 and 35/20°C. After 4 weeks at 5°C, initially-dormant seeds germinated to 100% at all thermoperiods except 35/20°C, where only 15% of them germinated. However, after 18 weeks at 5°C, only 0–1% of the seeds germinated at all thermoperiods. Most non-dormant seeds exposed to 1, 5 and 15/6°C for 16 weeks were induced into dormancy; 1–15% entered conditional dormancy and thus germinated only at 15/6, 20/10 and 25/15°C. This study indicates that seeds of winter annual plants of T. arvense are non-dormant in autumn and enter dormancy in winter, while those from summer annuals are dormant in autumn and become non-dormant during winter.     

Germination of Alternaria linicola conidia on linseed: effects of temperature, incubation time, leaf wetness and light regime

Conidia of Alternaria linicola germinated on both water agar and linseed leaves (detached or attached) over a wide range of temperatures (5–25°C) by producing one to several germ tubes. At temperatures between 10°C and 25°C and under continuous wetness in darkness, germination started within 2 h after inoculation and reached a maximum (100%) by 8 to 24 h, depending on temperature. At 5°C, the onset of germination was later and the rate of germ tube elongation was slower than that at 10–25°C. During germination, conidia of A. linicola were sensitive to dry interruptions of wet periods and to light. Short (2 h) or long (12 h) dry interruptions occurring at any time between 2 and 6 h after inoculation stopped conidial germination and germ tube elongation. With continuous wetness, light periods 2 to 12 h long immediately after inoculation inhibited conidial germination, which was resumed only when a dark period followed subsequently. However, germination and germ tube elongation of A. linicola conidia stopped and the viability of the conidia was lost during exposure to dry light periods immediately after inoculation with spore suspensions. Penetration of leaves by A. linicola was evident after 12 h and occurred mainly through epidermal cells (direct) with or without the formation of appressoria.     

Effects of maternal light environment on germination and morphological characteristics of Sicyos deppei seeds

The effect was studied of sunlight and far-red (FR) light during seed development, on seed quality and germination of Sicyos deppei G. Don. Seeds exposed to FR during development were lighter in colour and their weight, size and water content were significantly lower. Less than 10% of non-scarified freshly harvested seeds germinated. Scarified, freshly harvested seeds developed under sunlight had a partially negative photoblastic response; both red (R) and FR light inhibited germination. The highest and fastest germination occurred in darkness, probably due to the effect of the high photon flux densities on the phytochrome during seed development. Scarified seeds ripened under FR light, germinated well in FR light and in darkness, but R light inhibited germination. After 6 months of storage, the permeability of S. deppei seeds increased, the partially negative photoblastic response was lost and germination of scarified seeds increased. Specifically, in seeds developed under FR, germination in darkness was faster than for the other light treatments, but slow in darkness for seeds developed under sunlight. The physiological and morphological heteroblastic responses in S. deppei probably extend its seed germination and seedling recruitment periods.     

Seasonal changes in seed dormancy of Solanum nigrum and Solanum physalifolium

The seed dormancy cycle in Solanum nigrum and Solanum physalifolium was studied in relation to seasonal temperature. Seed lots of both species were buried in pots outdoors in a randomised complete block design with four replicates from November 2004 to November 2006. At regular intervals, samples of the seeds were randomly exhumed and tested for germination in incubators at three temperatures and light/darkness regimes. For both species, low winter temperature weakened dormancy and high temperature strengthened it. Dormancy induction mainly occurred from August to October in both species after experiencing warm temperatures. An exception from the general pattern of seed dormancy was however observed; seed germination percentages were temporarily reduced in early spring, followed by a peak in germination, before the main period of strong dormancy in S. nigrum . The same phenomenon was observed in S. physalifolium during June in the first year. This short-lived dormancy induction might explain the late emergence of the species. Seed dormancy enables the species to maximise its chance of survival by regulating germination timing to favourable conditions. Therefore, information on the dormancy cycle can be used to predict seedling emergence and optimise weed control operations.     

Seasonal changes in the germination responses of buried Lamium amplexicaule seeds

Spring-produced seeds of Lamium amplexicaule L. were buried in pots of soil in an unheated glasshouse in June 1978, and at 1–2-month intervals, for 27 months, they were exhumed and tested for germination in light and darkness at temperatures simulating those in the habitat from early spring to late autumn. Freshly-matured seeds were dormant, but by autumn 85% or more germinated in light at 15/6, 20/10, 25/15 and 30/15°C but only 7% or less in darkness. During late autumn and winter germination in light decreased at 25/15 and 30/15 °C but not at 15/6 and 20/10 °C, and germination in darkness increased at 15/6 and 20/10 °C. During late winter and early spring germination in light at 15/6 and 20/10 °C decreased, and seeds lost the ability to germinate in darkness. By the second autumn of burial, seeds germinated to near 100% in light at 15/6 to 30/15 °C and to 10–25% in darkness at 15/6 and 20/10 °C. The cycle of germination responses was repeated during the second winter and spring and the third summer of burial. Autumn-produced seeds were dormant when buried in November 1979, but by spring they germinated to 81 and 36% at 15/6 and 20/10 °C, respectively, in light. These seeds afterripened further during summer. The consequence of seasonal changes in germination responses is that (1) seeds can germinate in the habitat in late summer, autumn and spring but not in early- to mid-summer or in late autumn and winter and (2) during both germination seasons, seeds produced during the previous spring(s) and/or autumn(s) can germinate.     

Effect of burial depth and soil water regime on the fate of Lithospermum arvense seeds in relation to burial time

Lithospermum arvense is an increasing annual weed in winter crops of the semiarid region of southern Argentina under low impact tillage systems, an agricultural practice that has become popular in recent years. Seed distribution in the soil profile under conventional tillage will change when reduced tillage is implemented, thus affecting the germination microenvironment. The effect of seed burial depth and soil water regime on field germination, enforced dormancy, innate dormancy and seed decay was studied in relation to burial time in a field experiment. In addition, the effect of burial depth on seed germination and seedling emergence was examined under laboratory controlled conditions. Field germination of buried seed ranged from 55% to 65% for shallow (2 cm) and from 5% to 30% for greater depths (20 cm). Enforced dormancy levels were significantly higher among deeper seeds. The amount of innate dormant seeds was reduced to <10% after a year of burial. Lithospermum arvense seedbanks can be classified as short-term persistent. Germination in the laboratory was unaffected by burial depth, while seedling emergence reduction was adequately described by a sigmoidal model. Results indicate that agricultural practices that accumulate L. arvense seeds near the soil surface enhance seedling recruitment.     

Longevity,dormancy and germination of Cyanus segetum

Cyanus segetum is an iconic, colourful weed in arable fields that provides ecological and societal services. To understand better both the infestation dynamics of C. segetum as an abundant, harmful weed and maintain sustainable populations where it provides beneficial services, we compared information on seed dormancy, seed longevity and germination conditions in two populations. Persistence of seeds buried in the soil was low, with <10% viable after 3 years. Periodic dormancy cycling was observed over the 4 years in the soil, with a maximum of dormant seeds in the spring and a minimum in the autumn; however, 20% of the seeds were non‐dormant all the time. Seeds of C. segetum were positive photosensitive, but light requirement varied among populations. Base water potential for germination was ?1 MPa. Base temperature ranged from 1 to 2°C. Optimum temperature for germination was about 10 to 15°C, but the mean thermal time varied greatly between populations, from 80 to 134 day °C. Photoperiod and temperature combinations had no effect on germination percentage, but both reduced the germination rate. Burial deeper than 2 cm greatly reduced germination and seedling emergence strongly decreased at depths >0.5 cm. No seeds buried deeper than 8 cm emerged. Low seed longevity and a wide range of germination conditions could partly explain the rapid disappearance of C. segetum populations after herbicide application began in western Europe. However, yearly sowing in restoration areas does not seem to be essential.     

Role of temperature in regulating timing of germination in soil seed reserves of Lamium purpureum L.

Fresh seeds of Lamium purpureum L. were dormant at maturity, and when buried and exposed to natural seasonal temperature changes they exhibited an annual dormancy/non-dormancy cycle. During burial in summer, fresh seeds and those that had been buried for 1 year afterripened and thus were non-dormant by September and October; light was required for germination. During autumn and winter seeds re-entered dormancy, and during the following summer they became non-dormant again. Dormant seeds afterripened when buried and stored over a range of temperatures, becoming conditionally dormant at low (5, 15/6°C) and non-dormant at high (20/10, 25/15, 30/15 and 35/20°C) temperatures. Conditionally dormant seeds germinated to high percentages at 5, 15/6 and 20/10°C, while non-dormant seeds germinated to high percentages additionally at 25/15, 30/15 and 35/20°C. Low temperatures caused non-dormant seeds to re-enter dormancy, while high temperatures caused a sharp decline in germination only at 30/15 and 5°C. The temperature responses of L. purpureum seeds are compared to those of L. amplexicaule L.     

Ecological aspects of seed dormancy-break and germination in Heteranthera limosa (Pontederiaceae), a summer annual weed of rice fields

Summary Heteranthera limosa seeds were buried in flooded and in non-flooded soil and exposed to natural seasonal temperature changes in Lexington, Kentucky, USA. Seeds exhumed after various periods of burial ranging from 2 to 36 months were tested for germination under both flooded and non-flooded conditions. Seeds were dormant at maturity in September and became non-dormant during winter. Seeds buried in non-flooded soil during winter germinated to higher percentages and over a wider range of temperatures when tested under flooded conditions (in light) during spring and summer, than did those buried in flooded soil during winter. Thus, the water regime associated with rice culture (non-flooded in winter and flooded in summer) is optimal for dormancy-break and germination of H. limosa seeds. A portion of the buried seeds exhibited an annual dormancy/non-dormancy cycle, whereas others had a conditional dormancy/non-dormancy cycle. Regardless of the type of cycle, seeds buried in non-flooded soil retained the ability to germinate in light at high temperatures under flooded conditions throughout the summer. Thus, seeds potentially can germinate at any time during the growing season, whenever rice fields are flooded. Flooding fields during winter and/or sowing rice relatively early in the growing season may help in establishing rice before seeds of H. limosa germinate.