Analysis of developmental preformation in the alpine herb Caltha leptosepala (Ranunculaceae)

Developmental preformation is ubiquitous among alpine and arctic tundra plant species and may cause a delay in plant morphological responses to environmental variation. The duration of preformation and seasonal pattern of development were examined in Caltha leptosepala to identify characteristics of architecture and development that may influence the timing of plant responses to environmental cues, both within a single growing season and between years. All structures in C. leptosepala are preformed: leaves are initiated one or two growing seasons before they mature and flowers are initiated one growing season before maturation. Features of development and architecture in C. leptosepala, however, appear to differ from the determinate growth patterns of other exclusively preforming species, and may allow within-season variability in the seasonal development and maturation of structures. Cohorts of leaves initiated are asynchronous with maturation cohorts, and each year the number of leaf primordia per plant at snowmelt exceeds the number to mature aboveground. Therefore, some flexibility in whether leaves complete a 2-yr or 3-yr developmental trajectory might occur. Plasticity in reproductive phenotype might also occur via the process of floral abortion. Despite developmental characteristics that might facilitate the expression of phenotypic plasticity, only slight variability was observed in the duration of preformation or in the seasonal pattern of initiation and emergence of structures. Growth patterns of C. leptosepala thus appear to be fundamentally constrained, and limitations to annual growth may assure that sufficient preformed primordia remain belowground at the end of each growing season for maturation of a full cohort during the subsequent season.     

Periods of organogenesis in mono- and bicyclic annual shoots of Juglans regia L. (Juglandaceae)

The organogenetic cycle of shoots on main branches of 4-year-old Juglans regia trees was studied. Mono- and bicyclic floriferous and vegetative annual shoots were analysed. Five parent annual shoot types were sampled between October 1992 and August 1993. Organogenesis of summer growth units was monitored between 16 Jun. and 3 Aug. 1993. Variations over time in the number of nodes, cataphylls and embryonic green leaves of terminal buds were studied. The number of nodes of parent shoot buds was compared with the number of nodes of shoots derived from parent shoot buds. The spring growth units of mono- and bicyclic shoots consist exclusively of preformed leaves which were differentiated, respectively, during the spring flush of growth (mid-April until mid-May) or the summer flush of growth (mid-June until early August) in the previous growing season. Thus, winter buds may consist of flower and leaf primordia differentiated in two different periods during annual shoot extension. The summer growth units of bicyclic shoots consist of preformed leaves that were differentiated in spring buds during the spring flush of growth in the current growing season. Bud morphology is compared between spring and summer shoots.     

Leaf photosynthesis in pure swards of two grasses (Lolium perenne and Lolium multiflorum) subjected to contrasting intensities of defoliation

Photosynthetic rates were measured on light saturated, fully-expanded leaves in pure swards of Lolium perenne and Lolium multiflorum during late summer using 14-carbon dioxide. These swards were defoliated by cutting at three heights of 3, 6 and 9 cm above the ground. The photosynthetic rates of leaves on tillers in swards cut constantly 3 cm above ground level were higher than those of leaves in swards cut constantly 9 cm above ground level. Additional treatments with various sequences of cuts 3, 6 and 9 cm above ground level were designed to reduce damage to the growing points of tillers whilst ensuring satisfactory harvesting of the shoots. The photosynthetic rates of leaves on tillers cut to various heights above ground level at successive harvests were intermediate between those of similar leaves in the constantly low and high cut swards. The rates of photosynthesis of Italian ryegrass leaves were higher than those of perennial ryegrass leaves for a short time after defoliation of the constantly high cut swards. However, these perennial ryegrass leaves quickly adapted their rates of photosynthesis to the higher irradiances they received after cutting. Thus grass species differing in morphology adjust to management practices by the use of different photosynthetic strategies.     

Individual variation and the effects of weather, age and flowering history on survival and flowering of the long-lived perennial Gentiana pneumonanthe

Gentiana pneumonanthe , the marsh gentian, is a declining species in both Britain and Europe as a result of loss of its heathland habitat or inappropriate management of that which remains. We analysed long-term demographic data sets (1977-1991) from four populations of the plant to test the hypotheses that an individual plant's survival and its chances of flowering in any year are related to its age and performance in previous years, taking into account the climatic conditions that existed in those years The results show that: 1)'new'plants (2 yr old) had a higher mortality rate (mean = 20.8%) than'young'(3 yr old) plants (mean = 5.0%), which in turn had a higher mortality than older, 'mature' (four or more year old) plants (mean = 3.8%): 2)'new' plants had a higher mortality rate after either a growing season with below average rainfall or an above average winter rainfall; 3) mortality of'mature'plants was independent of age, indicating no evidence of senescence; 4)'mature'plants had a higher mortality rate after above average rainfall during the previous winter; 5) plants that have flowered within the previous two years are most likely to flower in the current year indicating high individual variation in flowering performance- 6) more plants flower and flowering plants produced more flowers in the two years following a warmer than average growing season.
The above factors are related to current site management and the implications are discussed. Suggestions are given for changes in management of the sites where this rare plant occurs.     

EFFECT OF DEFOLIATION ON GENDER EXPRESSION AND FRUIT SET IN PASSIFLORA INCARNATA

We examined the effect of defoliation on gender expression and fruit set in a north-central Florida population of the andromonoecious vine, Passiflora incarnata, during the 1984 flowering season. At three times during the flowering season (May, June, July), the leaves adjacent to flowers at four stages of development were removed, and subsequent sex and fate of each flower were determined. Defoliation affected gender of the flower by significantly decreasing the probability that the styles of the flower would deflex and the flower would thus function only as a pollen donor. Flowers were sensitive to defoliation at any stage before anthesis, though the sensitivity appeared to decrease in the most mature category of flower buds. Fruit set of hermaphroditic flowers remained unaffected by defoliation, but the probability of fruit set and gender expression were significantly influenced by the time of the flowering season. We conclude that the local photosynthate environment determines flower gender in Passiflora, but branch or entire plant photosynthate resources can compensate for local resource fluctuations and play an important role in fruit set and flower bud abortion. The sexual lability of Passiflora incarnata appears to be an adaptation to uncertain resource levels at a fine scale, caused by nearby developing fruits and the possibility of herbivore defoliation.     

Timing of reproductive and vegetative development in Saxifraga oppositifolia in an alpine and a subnival climate

Morphogenesis of floral structures, dynamics of reproductive development from floral initiation until fruit maturation, and leaf turnover in vegetative short-stem shoots of Saxifraga oppositifolia were studied in three consecutive years at an alpine site (2300 m) and at an early- and late-thawing subnival site (2650 m) in the Austrian Alps. Marked differences in the timing and progression of reproductive and vegetative development occurred: individuals of the alpine population required a four-month growing season to complete reproductive development and initiate new flower buds, whereas later thawing individuals from the subnival sites attained the same structural and functional state within only two and a half months. Reproductive and vegetative development were not strictly correlated because timing of flowering, seed development, and shoot growth depended mainly on the date of snowmelt, whereas the initiation of flower primordia was evidently controlled by photoperiod. Floral induction occurred during June and July, from which a critical day length for primary floral induction of about 15 h could be inferred. Preformed flower buds overwinter in a pre-meiotic state and meiosis starts immediately after snowmelt in spring. Vegetative short-stem shoots performed a full leaf turnover within a growing season: 16 (+/-0.8 SE) new leaves per shoot developed in alpine and early-thawing subnival individuals and 12 (+/-1.2 SE) leaves in late-thawing subnival individuals. New leaf primordia emerged continuously from snowmelt until late autumn, even when plants were temporarily covered with snow. Differences in the developmental dynamics between the alpine and subnival population were independent of site temperatures, and are probably the result of ecotypic adaptation to differences in growing season length.     

Using CO2 Efflux Rates to Indicate Below-Ground Growing Seasons by Land-use Treatment

CO₂ efflux rates are affected by vegetation type, temperature, and soil surface conditions, and serve as an indicator of the length of the below-ground biological and microbial growing season. This study determined the effect of three land-use treatments on CO₂ efflux and growing season lengths in Southeast Virginia on two forested mineral soil wetlands. CO₂ efflux, soil temperature, and soil moisture were measured 24 times in 18 months at plots representing forest, early successional field, and bare ground land-use treatments. CO₂ efflux differed (p < 0.05) by treatment in the order forest > field > bare ground. CO₂ efflux was higher in hardwood- than conifer-dominated forest and higher in bare ground plots that were not inundated. Appreciable CO₂ efflux took place even once leaves had fallen off deciduous trees, and most of the CO₂ efflux appeared to be from vegetation rather than microbial sources during that period. Variability in CO₂ efflux was best described by the interaction between soil temperature and soil moisture (R² = 0.32) (p < 0.05). The below-ground growing season indicated by appreciable CO₂ efflux was similar to that indicated by soil temperatures above 5°C measured at 50 cm, the regulatory reference depth. The CO₂ efflux growing season was 365 days in the forest but was 9–16 days shorter in the field and 21–78 days shorter in the bare ground land-use treatment plots. These data can be used to modify the regulatory growing season definition in forested thermic wetlands and to reflect the environmental variation caused by different land uses.     

Carbon and nitrogen partitioning in the biennial monocarp Arctium tomentosum Mill

Summary Growth and nitrogen partitioning were investigated in the biennial monocarp Arctium tomentosum in the field, in plants growing at natural light conditions, in plants in which approximately half the leaf area was removed and in plants growing under 20% of incident irradiation. Growth quantities were derived from splined cubic polynomial exponential functions fitted to dry matter, leaf area and nitrogen data.Main emphasis was made to understanding of the significance of carbohydrate and nitrogen storage of a large tuber during a 2-years' life cycle, especially the effect of storage on biomass and seed yield in the second season. Biomass partitioning favours growth of leaves in the first year rosette stage. Roots store carbohydrates at a constant rate and increase storage of carbohydrates and nitrogen when the leaves decay at the end of the first season. In the second season the reallocation of carbohydrates from storage is relatively small, but reallocation of nitrogen is very large. Carbohydrate storage just primes the growth of the first leaves in the early growing season, nitrogen storage contributes 20% to the total nitrogen requirement during the 2nd season. The efficiency of carbohydrate storage for conversion into new biomass is about 40%. Nitrogen is reallocated 3 times in the second year, namely from the tuber to rosette leaves and further to flower stem leaves and eventually into seeds. The harvest index for nitrogen is 0.73, whereas for biomass it is only 0.19.     

Internal oxygen levels decrease during the growing season and with increasing stem height

The oxygen levels in the sapwood of Norway spruce [Picea abies Karst. (L.)] trees were measured by GC-MS (gas chromatography – mass spectrometry) as stem growth progressed during the growing season. The measurements were made on 30-year-old, 13–15 m high, trees growing on three plots which were irrigated, left undisturbed or subjected to drought. The oxygen measurements were done at 1.5, 4 and 8 m above the ground. The internal oxygen levels dropped to about 5% of the level in air in irrigated trees, 1–3% in control trees and to below 1% in trees subject to drought between mid-July and mid-August. In the trees subjected to drought there where no differences in internal oxygen concentrations between the positions on the tree during the growing season except for a faster increase back to ambient concentration occurring in late August in the 1.5 m position. In trees growing on the two other plots the internal oxygen concentration was higher near the ground than at 4 or 8 m above ground during July and August. At all other dates there were no differences between the positions. The results indicate that there is an oxygen gradient with levels decreasing acropetally, giving indirect support to the hypothesis that oxygen is supplied to the growing stem in the transpiration stream. Received: 26 January 1999 / Accepted: 1 June 1999     

Dynamics of flower development and vegetative shoot growth in the high mountain plant Saxifraga bryoides L.

Saxifraga bryoides L. is an abundant species in the subnival and nival zone of the European mountains. First flowering occurs, at the earliest, 6 weeks after snowmelt. This is a remarkably long prefloration period in an environment with a short growing season. To gain more information about the developmental strategies of this species, the timing and the dynamics of flower bud formation and vegetative shoot growth were studied at sites with growing seasons of different lengths at two subnival locations (2650 and 2880 m a.s.l.) in the Tyrolean Alps. At an early, mid and late thawing site, individuals emerging from the winter snow were labelled. Reproductive and vegetative shoots were sampled at regular intervals throughout the growing season and analysed, using different microscopic techniques. Flower buds of S. bryoides develop in three cohorts. Provided the growing season is long enough, cohorts 1 and 2 come into flower, whereas cohort 3 buds remain primordial and continue to develop after winter. New flower primordia appear as day-length decreases from August on, which suggests a short-day requirement for floral initiation. At the end of the growing season, flower buds of different stages are present, but only primordial stages survive winter. Thus, flower buds of S. bryoides develop largely or even completely in the year of anthesis. Developmental dynamics were quite similar at the different sites. Time from flower initiation until anthesis took about 2 months, independently of whether flowers were formed within one or two seasons. All of the leaves on vegetative short-stem shoots turnover within a growing season. Leaves having passed winter continuously decline and are replaced by newly formed ones (21±3 at the mid-thawing site and 18±1 leaves at the short-season site). An individual leaf functions therefore, on average, about 12 months. In most years the seed crop of S. bryoides results mainly from the first cohort of flowers in an individual. In a changing climate with a prolonged growing season, the chance of two cohorts to develop mature seeds from flower cohorts 1 and 2 would increase.     

Population dynamics ofHeloniopsis orientalis C. Tanaka (Liliaceae) in natural forests — Annual life cycle

Annual changes in the leaves and reproductive organs ofHeloniopsis orientalis C. Tanaka (Liliaceae), a perennial evergreen herb, were studied from 1991 to 1997 in two areas of South Korea, Namhansanseong and Maranggol. The period for active growth in the leaves was from mid-March to early June. Average leaf angle was 70° in early June, decreasing to 50° in late October. From December until June of each following year, leaf angle was maintained a 0° to horizontal. The specific leaf area (SLA) value was 185 cm².g^-1 early in the growing season, increasing to 332 cm²g^-1 in early June. By the end of October, SLA had decreased to 159 cm²g^-1, after which it increased again from March to June. Because the SLA curve had two peaks, it was inferred thatH. orientalis possesses two means for survival: 1) an anti-freezing mechanism by which its leaves thicken during the winter, and 2) a reallocation of energy from old leaves to new leaves or to reproductive organs.H. orientalis flowered in a semi-enclosed state in late March. Blooming out of the bract, the front of the flower faced the ground. Growth of the peduncle ended in early June, at which point it was 60 cm long. At that time, the fruit was oriented so that the seeds were dispersed upward. Therefore one can see thatH. orientalis has two physiological features that enhance long-distance seed dispersal — a rather long peduncle relative to overall plant size and an upward seed-dispersal mechanism. In the Namhansanseong area, energy from the roots and old leaves was translocated to new leaves early in the growing season (from late March to early May). However, after mid-May, energy was re-translocated from new leaves to the roots. Moreover, the leaves on flowering plants grew more slowly than on non-flowering plants because energy was translocation to the reproductive organs. Therefore, new leaf growth depended on energy stores of the roots and the biomass of old leaves early in the growing season.     

SHOOT GROWTH AND LEAF DIMORPHISM IN BOSTON IVY (PARTHENOCISSUS TRICUSPIDATA)

Boston ivy, a common ornamental vine in the grape family, successively produces two kinds of leaves during the growing season. The two “early leaves” at the base of each shoot are preformed in the winter bud, and their expansion in the spring is accompanied by little stem elongation. At maturity they have large three-lobed blades and long petioles. Most short shoots produce no more leaves, but “late leaves” develop on all long shoots at intervals of less than 2 days. All but the first few undergo their entire development during the growing season. They are much smaller than early leaves, and the lateral lobes of their blades are reduced or eliminated. They are separated from the early leaves and from each other by long internodes. The early and late leaves differ in the circumstances and continuity of ontogeny, and diverge in form at an early stage. This vine and its relatives are unique in their three-node cyclical pattern of organ occurrence and internode length along the shoot. Lateral shoots and buds are present at every third node, with tendrils at intervening nodes. The long shoots branch freely and repeatedly, and the production of late leaves and new shoot axes by vigorous compound shoots is limited only by the growing season. Despite its specialized organization, Boston ivy resembles several tree species in its association between a seasonal type of leaf dimorphism and a shoot system constructed of long and short shoots.     

Elevated CO2 enhances water relations and productivity and affects gas exchange in C3 and C4 grasses of the Colorado shortgrass steppe.

Six open‐top chambers were installed on the shortgrass steppe in north‐eastern Colorado, USA from late March until mid‐October in 1997 and 1998 to evaluate how this grassland will be affected by rising atmospheric CO₂. Three chambers were maintained at current CO₂ concentration (ambient treatment), three at twice ambient CO₂, or approximately 720 μmol mol^?1 (elevated treatment), and three nonchambered plots served as controls. Above‐ground phytomass was measured in summer and autumn during each growing season, soil water was monitored weekly, and leaf photosynthesis, conductance and water potential were measured periodically on important C₃ and C₄ grasses. Mid‐season and seasonal above‐ground productivity were enhanced from 26 to 47% at elevated CO₂, with no differences in the relative responses of C₃/C₄ grasses or forbs. Annual above‐ground phytomass accrual was greater on plots which were defoliated once in mid‐summer compared to plots which were not defoliated during the growing season, but there was no interactive effect of defoliation and CO₂ on growth. Leaf photosynthesis was often greater in Pascopyrum smithii (C₃) and Bouteloua gracilis (C₄) plants in the elevated chambers, due in large part to higher soil water contents and leaf water potentials. Persistent downward photosynthetic acclimation in P. smithii leaves prevented large photosynthetic enhancement for elevated CO₂‐grown plants. Shoot N concentrations tended to be lower in grasses under elevated CO₂, but only Stipa comata (C₃) plants exhibited significant reductions in N under elevated compared to ambient CO₂ chambers. Despite chamber warming of 2.6 °C and apparent drier chamber conditions compared to unchambered controls, above‐ground production in all chambers was always greater than in unchambered plots. Collectively, these results suggest increased productivity of the shortgrass steppe in future warmer, CO₂ enriched environments.     

Changes in diffusible indole-3-acetic acid from various parts of tulip plant during rapid elongation of the flower stalk

In order to chemically identify the putative indole-3-acetic acid (IAA) and to confirm the native source of auxins account for rapid elongation of the floral stalk of tulip, we examined diffusible IAA from various parts of tulip plant during rapid elongation of the flower stalk. IAA was identified in the diffusates collected from the leaves, internodes, and floral organs with gas chromatography (GC)–mass spectrometry. The amount of diffusible IAA from different plant organs followed the order of that the internodes > flower organs > leaves during the period of rapid elongation of the floral stalk. The diffusible IAA from internodes reached its peak amount at different time than did diffusible IAA from the flower. The results obtained indicated that the top internode is probably the major source of auxins account for rapid elongation of the flower stalk.     

Impacts of a spring heat wave on canopy processes in a northern hardwood forest

Heat wave frequency, duration, and intensity are predicted to increase with global warming, but the potential impacts of short‐term high temperature events on forest functioning remain virtually unstudied. We examined canopy processes in a forest in Central Ontario following 3 days of record‐setting high temperatures (31–33 °C) that coincided with the peak in leaf expansion of dominant trees in late May 2010. Leaf area dynamics, leaf morphology, and leaf‐level gas‐exchange were compared to data from prior years of sampling (2002–2008) at the same site, focusing on Acer saccharum Marsh., the dominant tree in the region. Extensive shedding of partially expanded leaves was observed immediately following high temperature days, with A. saccharum losing ca. 25% of total leaf production but subsequently producing an unusual second flush of neoformed leaves. Both leaf losses and subsequent reflushing were highest in the upper canopy; however, retained preformed leaves and neoformed leaves showed reduced size, resulting in an overall decline in end‐of‐season leaf area index of 64% in A. saccharum, and 16% in the entire forest. Saplings showed lower leaf losses, but also a lower capacity to reflush relative to mature trees. Both surviving preformed and neoformed leaves had severely depressed photosynthetic capacity early in the summer of 2010, but largely regained photosynthetic competence by the end of the growing season. These results indicate that even short‐term heat waves can have severe impacts in northern forests, and suggest a particular vulnerability to high temperatures during the spring period of leaf expansion in temperate deciduous forests.     

Bud and growth-unit structure in seedlings and saplings of Nothofagus alpina (Nothofagaceae)

In temperate trees, axis length growth generally results from the differentiation of organs at the end of a growing season and the extension of such "preformed organs" in the next growing season. Neoformation, i.e., the simultaneous differentiation and extension of organs, has been studied for only a few species. Here we evaluated bud composition and growth unit (GU) size for seedlings and saplings of Nothofagus alpina, a valuable South American forest tree. Trunk GUs of seedlings and saplings included preformed and neoformed organs, whereas main-branch GUs of saplings were entirely preformed. The size of a GU was more closely related to the number of preformed green leaves than to the number of cataphylls of its preceding bud. Proximal buds of a trunk GU had more cataphylls and less green-leaf primordia than distal buds. Individual leaf area increased from proximal to distal positions on trunk GUs. For trunk and main-branch GUs, the length/width ratio was maximum for leaves in intermediate positions. The development of large neoformed leaves at the end of the growing season could increase the photosynthetic capacity of this species in late summer, when the activity of preformed organs is likely to be decreasing.     

Self‐ and intra‐morph incompatibility and selection analysis of an inconspicuous distylous herb growing on the Tibetan plateau (Primula tibetica)

There is discussion over whether pollen limitation exerts selection on floral traits to increase floral display or selects for traits that promote autonomous self‐fertilization. Some studies have indicated that pollen limitation does not mediate selection on traits associated with either pollinator attraction or self‐fertilization. Primula tibetica is an inconspicuous cross‐fertilized plant that may suffer from pollen limitation. We conducted a selection analysis on P. tibetica to investigate whether pollen limitation results in selection for an increased floral display in case the evolution of autonomous self‐fertilization has been difficult for this plant. The self‐ and intra‐morph incompatibility features, the capacity for autonomous self‐fertilization, and the magnitude of pollen limitation were examined through hand‐pollination experiments. In 2016, we applied selection analysis on the flowering time, corolla width, stalk height, flower tube length, and flower number in P. tibetica by tagging 76 open‐pollinated plants and 37 hand‐pollinated plants in the field. Our results demonstrated that P. tibetica was strictly self‐ and intra‐morph incompatible. Moreover, the study population underwent severe pollen limitation during the 2016 flowering season. The selection gradients were found to be significantly positive for flowering time, flower number, and corolla width, and marginally significant for the stalk height. Pollinator‐mediated selection was found to be significant on the flower number and corolla width, and marginally significant on stalk height. Our results indicate that the increased floral display may be a vital strategy for small distylous species that have faced difficulty in evolving autonomous self‐fertilization.     

Linking above-ground and below-ground effects in autotrophic microcosms: effects of shading and defoliation on plant and soil properties

Although factors affecting plant growth and plant carbon/nutrient balance – e.g., light availability and defoliation by herbivores – may also propagate changes in below‐ground food webs, few studies have aimed at linking the above‐ground and below‐ground effects. We established a 29‐week laboratory experiment (～one growing season) using autotrophic microcosms to study the effects of light and defoliation on plant growth, plant carbon/nutrient balance, soil inorganic N content, and microbial activity and biomass in soil. Each microcosm contained three substrate layers – mineral soil, humus and plant litter – and one Nothofagus solandri var. cliffortioides seedling. The experiment constituted of the presence or absence of two treatments in a full factorial design: shading (50% decrease in light) and artificial defoliation (approximately 50% decrease in leaf area in the beginning of the growing season). At the end of the experiment a range of above‐ground and below‐ground properties were measured. The shading treatment reduced root and shoot mass, root/shoot ratio and leaf production of the seedlings, while the defoliation treatment significantly decreased leaf mass only. Leaf C and N content were not affected by either treatment. Shading increased NO ₃–N concentration and decreased microbial biomass in humus, while defoliation did not significantly affect inorganic N or microbes in humus. The results show that plant responses to above‐ground treatments have effects which propagate below ground, and that rather straightforward mechanisms may link above‐ground and below‐ground effects. The shading treatment, which reduced overall seedling growth and thus below‐ground N use and C allocation, also led to changes in humus N content and microbial biomass, whereas defoliation, which did not affect overall growth, did not influence these below‐ground properties. The study also shows the carbon/nutrient balance of N. solandri var. cliffortioides seedlings to be highly invariant to both shading and defoliation.     

Study on the Annual Periodicity of Growth and Development of Friellaria Palldiclora Schrenk

According to the observations under the climate at 1700 meters above sea level of mountainous district, the annual periodity of growth and development of fritillary (Fritillaria pallidifora Schrenk.) is briefly described as folldowing: The young shoot sprouts out of the bulb and emerges from the soil in April every year, and forms flowers and fruits in succession. During this period the nutrients of underground bulbs exhaust themselves and a new buld is thereby regenerated. In the middle of June, the aerial part dried up. The regeneration bud in the underground bulb differentiats itself under the condition of 8–22 ℃ in surmruer and an axillary bud is simultaneously initiated. The bulb thus formed dormants in the winter. The growing period of fritillary is only 80–90 days above the ground and 270–280 days beneath the ground. Hence, the whole developmental process of a regeneration bud of fritillary has to pass through three successive growing seasons under the normal conditions in which the growth confined to the inside of bulb lengthens to 600 days approximately. With comparison of the other bulbous plants the characteristics of the development of fritillary may be defined as follows: 1. The regeneration bulb can be formed under the condition of short-day light on even under complete darkness. In contrast with fritillary, the formation of new bulb of onion and other bulbous plants occurs under the longdag light. 2. It is certainly known that a critical size of rhizome or bulb is required for flower formation of Iris and tulip. A similar phenomena has been observed for fritillary in the present experiment. The critical size of bulb for flower initiation of fritillary is taken by us as 1.8–2.7 girfresh weight and 1.2–2.2 cm in diameter. This has nothing to do with the age of the bulb. 3. Different optimum tempertures are neccessary for various developmental stages of fritillary respeetivtly. The normal development periodicity of fritillary may be modified by the onset of dormancy under the condition of low temperatures. Using this method, a secondary shoot will grow up in one growing season. This is in confirmation of the report on the experiment of an other fritillary.     

Snow cover and extreme winter warming events control flower abundance of some,but not all species in high arctic Svalbard

The High Arctic winter is expected to be altered through ongoing and future climate change. Winter precipitation and snow depth are projected to increase and melt out dates change accordingly. Also, snow cover and depth will play an important role in protecting plant canopy from increasingly more frequent extreme winter warming events. Flower production of many Arctic plants is dependent on melt out timing, since season length determines resource availability for flower preformation. We erected snow fences to increase snow depth and shorten growing season, and counted flowers of six species over 5 years, during which we experienced two extreme winter warming events. Most species were resistant to snow cover increase, but two species reduced flower abundance due to shortened growing seasons. Cassiope tetragona responded strongly with fewer flowers in deep snow regimes during years without extreme events, while Stellaria crassipes responded partly. Snow pack thickness determined whether winter warming events had an effect on flower abundance of some species. Warming events clearly reduced flower abundance in shallow but not in deep snow regimes of Cassiope tetragona, but only marginally for Dryas octopetala. However, the affected species were resilient and individuals did not experience any long term effects. In the case of short or cold summers, a subset of species suffered reduced reproductive success, which may affect future plant composition through possible cascading competition effects. Extreme winter warming events were shown to expose the canopy to cold winter air. The following summer most of the overwintering flower buds could not produce flowers. Thus reproductive success is reduced if this occurs in subsequent years. We conclude that snow depth influences flower abundance by altering season length and by protecting or exposing flower buds to cold winter air, but most species studied are resistant to changes.