Phenology and reproductive biology of eelgrass (Zostera marina L.) at Bahia Kino,sea of Cortez,Mexico

At Bahia Kino, Mexico, seeds of Zostera marina L. (eelgrass) germinate in October and early November. By January seedlings are widespread throughout the area. A very rapid vegetative growth ensues. By March all eelgrass at the depth limit (7 m) is flowering; and most is flowering in shallow water (low tide to 4 m depth). In April all plants are in flower; a few plants display mature seeds. Windrows of detached plants occur on the beaches. In May all reproductive plants have mature seeds, and few attached plants remain. In July all eelgrass in the area has disappeared.All reproductive activities and plant detachment are completed before the lethal upper limit for the species is reached (30°C). Thus, eelgrass at Bahia Kino is a true annual and represents an ultimate response to high water temperatures.     

Fire Season Effects on Flowering Characteristics and Germination of Longleaf Pine (Pinus palustris) Savanna Grasses

Pinus palustris (longleaf pine) savannas depend on contiguous grass cover to facilitate frequent surface fires. Enhanced flowering, seed production, and germination may be linked to season of fires. We assessed the effect of month of prescribed fire (February, April, May, and July) on percentage of plants with flowering culms (FCs%), FC/area, FC/plant, seed production, and germination for five warm seasons, fall‐flowering grasses. Multivariate analysis indicated the response of flowering and fruiting to burn month varied among the grass species. The dominant species, Sporobolus junceus and Schizachyrium scoparium var. stoloniferum, had greater numbers of most flowering characteristics when burnt during April, May, and July. Aristida purpurascens had increased FC/plant after May and July burns. In contrast, Ar. mohrii had the fewest FC/plant and seeds/FC when burnt in July. Germination was greatest (26–60%) for Ar. purpurascens. Seeds collected following July burns for Ar. purpurascens and Ar. ternarius and after May burns for S. junceus were within the highest germination values recorded. Germination of Sc. scoparium var. stoloniferum was very low after February and July burns (≤5%). With Ar. mohrii, only seed collected following February (2%) and April burns (3%) germinated. April, May, and July fires increased seed production of dominant matrix grasses, thus facilitating the potential for recruitment of these species and facilitating seed collection from potential donor sites for ground‐layer restoration projects. Varying prescribed fire burn month captured variation in flowering characteristics among these grasses.     

Magnitude and timing of leaf damage affect seed production in a natural population of Arabidopsis thaliana (Brassicaceae)

Background

The effect of herbivory on plant fitness varies widely. Understanding the causes of this variation is of considerable interest because of its implications for plant population dynamics and trait evolution. We experimentally defoliated the annual herb Arabidopsis thaliana in a natural population in Sweden to test the hypotheses that (a) plant fitness decreases with increasing damage, (b) tolerance to defoliation is lower before flowering than during flowering, and (c) defoliation before flowering reduces number of seeds more strongly than defoliation during flowering, but the opposite is true for effects on seed size.

Methodology/Principal Findings

In a first experiment, between 0 and 75% of the leaf area was removed in May from plants that flowered or were about to start flowering. In a second experiment, 0, 25%, or 50% of the leaf area was removed from plants on one of two occasions, in mid April when plants were either in the vegetative rosette or bolting stage, or in mid May when plants were flowering. In the first experiment, seed production was negatively related to leaf area removed, and at the highest damage level, also mean seed size was reduced. In the second experiment, removal of 50% of the leaf area reduced seed production by 60% among plants defoliated early in the season at the vegetative rosettes, and by 22% among plants defoliated early in the season at the bolting stage, but did not reduce seed output of plants defoliated one month later. No seasonal shift in the effect of defoliation on seed size was detected.

Conclusions/Significance

The results show that leaf damage may reduce the fitness of A. thaliana, and suggest that in this population leaf herbivores feeding on plants before flowering should exert stronger selection on defence traits than those feeding on plants during flowering, given similar damage levels.     

L'Influenza Delle Condizioni Fotoperiodiche e Termiche Sull'Accrescimento e Riproduzione della Salvia Longistyla Benth

Summary

Observations on growth and development of Salvia longistyla Benth., in several photoperiodic and termoperiodic conditions, both natural and artificial, were performed. The conclusions of my work are the following

I° - It has been proved that Salvia longistyla is a typical short-day plant and that its critical point of reaction lies approssimately on the 14 hours, when the average night-temperature is about 18°C; the flowering does not succeed if the night-temperature is decidedly below 15°C.

II° - The plant' requires short-day conditions not only for the formation of the flower buds, but also for the subsequent development, i. e. the full bloom; consequently the plant belongs to Eguchi's S. S. class (short day-plant for both the manifestations).

III. - Under natural conditions, in our latitude, Salvia longistyla flowers only in Autumn, because only in this season we have suitable photoperiod and concomitantly suitable night-temperature. In Spring, though the day is short, the night-temperature is not sufficiently high; in Winter and in Spring, the flowering is possible only in a warm green-house, with a night-temperature of about 18°C. In orange green-houses Salvia longistyla can continue the flowering begun in Autumn; during Winter and Spring new blooms do not succeed, just because the night-temperature, in such green houses, is never sufficiently high.

IV. - We can obtain fruiting only by artificial pollination (lack of natural pollination agency).

V. - The basal branches do not flower even in optimal photo- and termoperiodical conditions (which allow apical flowering) on acount of a mechanism of correlative inhibition.

VI. - The elongation of the internodes is relatively inhibited at a very long photoperiod, differently from what we observe in most plants.

These prerogatives, verified in repeated experiments, are in perfect accordance with the characteristics of the ambient in which the plant is naturally diffused (Mexico). The altitude and latitude of the stations in which the plant has usually been found, have a short photoperiod all year long, and temperatures (also night-temperatures) costantly suitable for a good growth and bloom. The plants, in the natural ambient, are perennial and bushy. The pluri-annuality can be referred to the flowering inhibition of the lateral and basal branches, that takes place in a specimen and that keeps on for a long time, also after the full flowering of the principal axis. The basal shoots show a tendency to the vegetative growth, even though the external conditions are suitable to the flowering of the apical parts of the plant. Therefore we must attribute the pluriannuality of S. longistyla to this correlative flower-inhibiting mechanism.     

Life-history variation in the short-lived herb <Emphasis Type="Italic">Rorippa palustris</Emphasis>: effect of germination date and injury timing

Life-history variation in annuals is known to be caused by size requirements for photoinduction of flowering, but the importance of germination date and injury was overlooked so far even though they may play an important role in disturbed habitats. To test the effect of germination date and timing of injury on life-history variation of an annual plant, we performed a 2-year pot experiment with the root-sprouting herb Rorippa palustris. Plants belonging to six different cohorts, and sown at monthly intervals from April to September, were injured (all stem parts removed) in three ontogenetic stages: vegetative rosettes, flowering plants and fruiting plants. Plants from the April, and partly from the May, cohort behaved as summer annuals: they started to bolt at the same time, resprouted and overwintered poorly. Plants from the June cohort flowered in the first season as well, but they entered the bolting stage a month later than the preceding cohorts, produced the least fruits, but overwintered successfully and flowered again the second year (polycarpic perennials). Cohorts germinating after the summer solstice did not flower during the first year and, with the exception of the September cohort, overwintered successfully and flowered the second year (winter annuals). After injury, the pattern of life-histories was the same as in control plants, although generative reproduction was interrupted by injury in the first year of the experiment. About one quarter of␣plants injured in the vegetative stage regenerated after injury irrespective of cohort, however, regeneration was enhanced in larger plants. Regeneration of plants in the flowering and fruiting stages depended on date of injury in relation to day length, being the most successful after the summer solstice. Life-history variation, together with the ability to resprout after severe injury in the pioneer wetland herb Rorippa palustris is caused by its ability to germinate throughout the season. Even the second tested factor, the effect of injury, is modified by germination time. The experiment points to a complex nature of factors affecting life-history variation as well as resprouting after severe injury in short lived plants. An erratum to this article can be found at     

Distribution of plant‐dwelling spiders: Inflorescences versus vegetative branches

Abstract The influence of the architecture of vegetative branches on the distribution of plant‐dwelling spiders has been intensively studied, and the effects on the aggregation of individuals in several spider species on plants include variation in prey abundance, availability of predator‐free refuges and smoother microclimate conditions. The emergence of inflorescences at the reproductive time of the plants changes branch architecture, and could provide higher prey abundance for the spiders. The distribution of spiders between inflorescences and vegetative branches was compared on four widespread plant species in a Brazilian savannah‐like system. Inflorescences attracted more spiders than vegetative branches for all plant species sampled. The influence of branch type (inflorescence and vegetative) on spider distribution was also evaluated by monitoring branches of Baccharis dracunculifolia DC. in vegetative and flowering periods for 1 year, and through a field experiment carried out during the same period where artificial inflorescences were available for spider colonization. Artificial inflorescences attached to B. dracunculifolia branches attracted more spiders than non‐manipulated vegetative branches for most of the year. However, this pattern differed among spider guilds. Foliage‐runners and stalkers occurred preferentially on artificial inflorescences relative to control branches. The frequencies of ambushers and web‐builders were not significantly different between treatment and control branches. However, most ambush spiders (65%) occurred only during the flowering period of B. dracunculifolia, suggesting that this guild was influenced only by natural inflorescences. The experimental treatment also influenced the size distribution of spiders: larger spiders were more abundant on artificial inflorescences than on vegetative branches. The hypothesis that habitat architecture can influence the spider assemblage was supported. In addition, our observational and experimental data strongly suggest that inflorescences can be a higher quality microhabitat than non‐reproductive branches for most plant‐dwelling spiders.     

L'evoluzione della cerchia legnosa in Quercus Pubescens W. Ein Quercus Ilex L. nel clima di Firenze

Summary

The evolution of the wood ring in Quercus pubescens W. and in Quercus Ilex L. in Florence (from June 1946 to June 1947).

The present study deals with the anatomical characters of the wood ring of Q. pubescens and of Q. Ilex. In both the specimens the wood of the stem and of the young branch has been investigated.

In both plants studied the cambial tissue of the stem starts dividing at the end of April, reaching its maximum activity from May to June.

On the contrary the cambium of the branch differentiates in Q. pubescens a month earlier (18 March-18 April) than in Q. Ilex (18 April-18 May). While in the branch of Q. Ilex a false ring can be seen corresponding to the autumn months, nothing of the kind is found in the branch of Q. pubescens; though it presents a false ring in the stem.

It is difficult to date clearly the period when the cambium stops its activity, but probably it happens at the end of August in the samples of the stem.

The leaf buds of Q. pubescens and of Q. Ilex open during April-May and the young branch is completely developed at the end of June. In both oaks some buds open in autumn, but the small branches are prevented to develop because of the cold.

No comparison can be made between the opening of the buds and the beginning of the cambial activity in the stem and in the branch.

Considering the evolution of these woods and their relationship to climatic factors, we can see that the cambial activity starts during a period of remarkable rainfall and of regular increase of temperature, and stops almost completely at the end of July, when temperature and dryness reach their highest values.

The autumn rainfall would favour again a cambial activity, but the values of the temperature, regularly decreasing, do not allow it.     

Andamento Dell'Accrescimento Del Legno in Ceratonia Siliqua L.

Abstract

The woody tissue of Ceratonia siliqua is of the diffuse-porous type, being mainly constituted of fibres full of starch grains (sostitution fibres; fusiform cells of the wood parenchyma).

The wood formed throughout the year is uniform and the annual rings are hardly distinguishable except for the presence of apotracheal parenchyma. The cambium shows a marked activity from May to July, and a less pronounced one from July to September; it is hardly or not at all active from October to April. During these latter months the cambium is completely dormant only in January, while during the others, especially the ones prior to the late spring reawakening, it can function in localised areas for short lapses of time.

These observations have been carried out in a female plant cultivated in Apulia, a region where Ceratonia siliqua is not a normal component of the natural plant cover. It is of some interest therefore to compare them with what is known of the same species in Israel, where C. siliqua is a spontaneous element of the maquis vegetation. The behaviour of the cambium of C. siliqua is similar in both regions but in Israel the maximum of activity begins earlier in the year and last for a longer period (mid-April to mid- August), after which the cambium becomes gradually less active until its activity is reduced to a minimum during autumn and winter. A short period of dormancy precedes the spring-time reawakening. This subcontinuous activity of the cambium together with the occurrence of flowering time in autumn-winter shows C. siliqua to be a tropical type of plant, but is nevertheless in good agreement with the eastern mediterranean climate.

In Apulia on the other hand we notice that the subcontinuous activity of the cambium is more potential than real, giving rise to sporadic and localised episodes from October to May. While this and other differences can be interpreted as direct responses to local climatic conditions, the general disturbances in the vegetative cycle can not be explained in the same way. In other words while the tendency of the cambium to remain dormant from October to May is probably caused by the relatively severe winter conditions, the shorter period of functioning in the spring—summer, the full resting period occurring in January rather than in February-March, and the attempts to resume meristematic activity already in February, while the full reawakening only occurs in May, can only be ascribed to indirect climatic action. These disturbances are probably to be seen as conseguences of the fact that the climatic conditions during the Apulian summer allow the flowers, whose primordia are well evident in July, to blossom in October-November and exceptionally even in August that is at least one month earlier than in Israel, where flowering occurs in December. This alteration in the flowering time affects the rythm of cambial activity causing it to be out of phase with the climatic cycle.

C. siliqua appears therefore not to be perfectly adapted to the Apulian climate even though it can often be found where it could not possibly have been planted, as on the steep flanks of fairly deep gulleys, and can be considered to be at least sub-spontaneous.     

Life cycle and growth ofPotamogeton crispus L. in a shallow pond,ojaga-ike

The life cycle and growth ofPotamogeton crispus L. were studied in a shallow pond, Ojaga-ike. With respect to the shoot elongation and seed and turion formations, the life cycle of this plant in the pond could be divided into following five stages: germination, inactive growth, active growth, reproductive and dormant stages. It was suggested that the plant showed these successive stages depending mainly upon water temperature. The turions germinated on the bottom in autumn when the water temperature fell below ca. 20 C. The plant showed hardly any growth during winter (December—early March) when the temperature was below 10 C. In the spring when the bottom water temperature rose to above 10 C (mid-March), the plant started to grow again and the shoot elongated rapidly at the rate of 4.2 cm day⁻¹ until the shoot apex reached the pond surface in late April. Both the increment of node number and the internodal elongation were associated with this rapid shoot growth. On 10 May (last sampling date), the mean values of shoot length, internodal length and the number of nodes estimated for 10 predominant plants were 238.2±5.6 cm, 7.1±0.8 cm and 34.9±4.0 cm, respectively. The turion formation and flowering occurred during the period from mid-April to mid-May when the surface water temperature ranged 19 and 22 C. The dry weight of a plant reached the maximum mean value of 1180 mg on 10 May. At its peak biomass, an individual plant produced 1–10 turions (5.5 on average) of which the mean individual turion dry weight was 53.2 mg. The turion dry weight accounted for ca. 42% of the total plant biomass m⁻² at that time.     

Conservation and storage of a haploid cucumber (Cucumis sativus L.) collection under in vitro conditions

 Over 3 consecutive years (1992–1994), a collection of cucumber haploids was obtained from three different lines and one hybrid. Attempts were made to maintain and store a subcollection of these haploids for 3 years. Cucumber haploids appeared to be stable when cultured in vitro. There were no instances of spontaneous doubling and only one morphologically changed plant. During the first year of storage, between 30% and 80% the clones were lost, due to disturbances in plant development, increased levels of endogenous bacteria, and physiological changes resulting in continuous flowering. After 2 years of storage haploids showed reduced vigour. Therefore, plants were regenerated directly from primordial leaf microexplants. Haploid plants were obtained from nearly all of the previous haploid plants. The rejuvenated haploids possessed the same ploidy level and morphological traits as the old collection. The only new characteristic was faster vegetative growth. Received: 17 March 1998 / Revision received: 14 April 1999 / Accepted: 10 May 1999     

Abundances of thrips on plants in vegetative and flowering stages are related to plant volatiles

Western flower thrips (WFTs), Frankliniella occidentalis Pergrande, and onion thrips (OTs), Thrips tabaci Lindeman, are two cosmopolitan insect pests of agricultural and horticultural plants. Understanding the occurrence and development of thrips on plants is crucial for identifying suitable plants that can be used for developing a “push-pull” strategy against thrips. In this study, the dynamics of WFTs and OTs on plants (Allium fistulosum L., Medicago sativa L., Luffa cylindrica (L.) Roem., Ocimum basilicum L., and Schizonepeta tenuifolia (Benth.) Briq.) were investigated for two consecutive years (2018–2019). Throughout the survey, the abundances of both thrips species were strongly associated with plant species and plant phenology; both thrips species were present at relatively high densities on M. sativa but very low densities on O. basilicum and S. tenuifolia. Populations of both thrips species greatly increased during plant flowering. A Y-tube olfactory test was used to study the effects of plant volatiles in mediating thrips behaviour and showed that volatiles of M. sativa were attractive to both thrips species whether emitted by the plant in the vegetative or flowering stage, while volatiles of O. basilicum and S. tenuifolia were repellent to thrips. Additionally, because of the presence of a high number of floral chemicals, both thrips species exhibited a greater preference for volatiles emitted by plants in the flowering period over those emitted by plants in the vegetative period. Our observations indicate that plant species and flowering status play an important role in the abundance dynamics of thrips and that the volatiles of flowering plants attract thrips more strongly than volatiles emitted by vegetative plants. These findings can facilitate the screening of attractive/unattractive plants for developing push-pull strategies to control thrips.     

Life-cycle and foraging patterns of native <Emphasis Type="Italic">Bombus terrestris</Emphasis> (L.) (Hymenoptera,Apidae) in the Mediterranean region

Life-cycle and foraging patterns of native Bombus terrestris populations were investigated at two sites in the Mediterranean region of Turkey, Phassalis (0 – 100 m above sea level [a.s.l.]) and Termessos (500 – 700 m a.s.l.). Bumble-bee activity was recorded during standard bee walks from November 2003 until the end of October 2004, each site being visited three times every month during the one-year period. The yearly dynamics of flight, the flowering plant species visited, and the visitation frequencies of these plants were recorded during every bee walk at both sites. There were considerable differences between the two populations with regard to the dates when the queens emerged from diapause (the emerging season), the timing of the appearance of sexuals (young queens and males), and the total number of plant species visited. Bombus terrestris queens emerged from diapause in November-December at the Phassalis site (coastal area) and in February-March at the Termessos site. The queens aestivated at the Phassalis site, whereas they hibernated at the Termessos site. Only one generation per year was produced at each site. The duration of the queens’ diapause lasted 5 – 8 months and length of the life cycle 190 – 215 days. Native B. terrestris populations were noted to forage on 47 flowering plant species from 20 families (10 at the Phassalis site and 40 at the Termessos site) during the study period. Two of the plant species (Arbutus unedo L. and Vitex agnus-castus L.) have long flowering periods and play a crucial role in the life cycle of native B. terrestris populations. The emergence of queens at the aestivation site was synchronized with the flowering of Arbutus unedo L., while the emergence of sexuals coincided with the flowering of Vitex agnus-castus L. at both sites. Received 30 May 2007; revised 5 December 2007; accepted 8 January 2008.     

Sviluppo Vegetativo E Riproduttivo Di Alcune Longidiurne in Rapporto All'Azione Dell'Acido Gibberellico

Summary

Continuing the experiments on the action of Gibberellic acid on growth and development of herbaceous plants, the Authors have examined once more several species which require “long day” for espletion of some phases of their reproductive development.

The principal aim was to bring into evidence whether Gibberellic acid can really substitute for some manifestations of the reproductive development itself, or whether some apparent manifestations of reproductive development provoked by this substance are due primarily to modifications of vegetative processes determinated by it.

The experiments were carried out on Papaver somniferum L., Centaurea calcitrapa L., Oenothera acaulis L., Aethusa Cynapium L. and Myosurus minimus L.

Results obtained on Papaver somniferum demonstrate that Gibberellic acid accelerates the macroscopic flowering manifestations under short day conditions of plants already induced to flowering, substituting in this for the effect of “long day” factor in so far as concerns the lengthening of the floral axis. No experiments which can establish whether Gibberellic acid may have an action on specific processes involved in the transition to the reproductive stage, have so far been conducted on Papaver.

Experiments on Centaurea calcitrapa have revealed that Gibberellic acid, treatment though promoting in plants manteined in short-day conditions a “bolting” effect simulating that obtained usually only at long-day, does not succeed in flowering this is true in our experimental conditions (experiments limit: 10 weeks; (photo-phase at light intensity inferior to 2000 lux). Experiments on Centaurea were also supplemented with histological observation of esperimental material.

In the experiments on Oenothera acaulis, a long-day plant only for the macroscopic development phase of floral apparatus, and indeterminate for the formation of floral primordia, has been noted that Gibb. acid can, in the long run, partly substitute for the long-day effect. However, development of floral structures at shortday, is more easily obtained if the plants are supplied, besides with Gibberellic acid, also with other stimulating and trophic substances. This and others observations may indicate that Gibberellic acid represent only one of the substances involved in the metabolism of plants under long-day conditions.

Aethusa Cynapium has furnished results similar to those obtained with Centaurea, even if within very long experimental limits some apparently indirect action of Gibberellic acid towards flowering may occurs.

Preliminary experimental data on logday Myosurus minimus L. show that Gibberellic acid can substitute sooner or later for longday requirements in flowering. In fact, two months old plants flower when Gibberellic acid is supplied under 9 hr. shortday conditions while the controls in shorday remain vegetative. We must note that Myosurus flowers better when light extension is prevalently constituted by far red radiation the effect of which is apparently substituted more easily by Gibberellic acid even if its action appears less afficient and rapid than that of supplementary illumination.     

Differenze Morfologiche ed Anatomiche in Individui Maschili E Femminili di Ginkyo Biloba L.

Abstract

Anatomical and histological differences between ♀ and ♂ plants of GINKYO BILOBA L. — Morphological characters in several ♀ and ♂ specimens of Ginkyo have been checked, with the aim to put in evidence those which are sex-linked. Anatomical data from a previous research have been utilized. (Maugini 1965).

The main results are here summarized.

In the climate of Florence the female plants unfold their buds in the first ten days of April, the male ones in the middle of March, so that the males break their dormancy about one month before the females.

From the buds opening, brachyblasts are formed both in males and females, and catkins and ovules appear. At the beginning of May, the ovules have considerably grown, and catkins are faded. In the meanwhile the leaves have completely grown up in both sexes. Between the end of September and the beginning of October, the seeds become gold-yellow and begin to be shed off. Dissemination may go on for a long while, and still be active when all the leaves are fallen.

Buds are formed during summer, they are very little and sharp in the female, round and bigger in the male.

In both sexes leaves turn yellow and begin to fall between the end of October and the beginning of November. Females are generally considered more precocious than males in shedding leaves, but this behaviour did not result constant in the plants under observations so that the « leaf-fall time » cannot be considered a sex-linked character.

In shoots and stems of males and females, proceeds downwards tracheid deposition and differentiation, the highest activity being in the brachyblasts, where cambium works continuosly, and the lowest in the stem, where late wood formation can be found only in the male plants. Unevenness of cambial activity along the plant axis is particularly evident in the female, where late wood formation in the stem is rare.

The rhythm of cambial activity along shoots and stems of males and females have been compared with that of the buds, with the following results: both in the female and male plants the young leaves start expanding about two months before cambium activity starts in the stem. The male plant is more precocious than the female, probably the slower vegetation rhythm of the female being related to the seed ripening process.     

Effects of diurnal and bidiurnal photoperiodic treatments on mitosis in Pharbitis

Abstract

Photoperiodic effect on mitotic activity of buds from dwarf Pharbitis has been analyzed. No significant differences in mitotic activity were found in plants grown under long days or diurnal (24 h) light break photoperiodic treatments. Differences in both mitotic activity and flowering were seen in plants subjected to diurnal short days, bidiurnal (48 h) short days, or bidiurnal short days with light breaks. An elevation of mitotic activity occurs in plants grown in bidiurnal photoperiodic treatments compared to diurnal treatments. The differences in mitotic activity of buds, both vegetative and floral, seem to indicate that both phytochrome and light effect on an endogenous rhythm influence meristematic activity. Also, the extended dark period of a bidiurnal short day enhances both mitosis and flowering.     

Evaluation of evidence for the presence of indole-3-acetic acid in marine algae

Summary Excretory products from aphids feeding on flowering and vegetative Xanthium plants contained a cytokinin active in the soybean-callus assay. No cytokinin activity was found in honeydew collected from aphids feeding on a chemically defined diet. Soybean-callus assays indicated that honeydew from aphids feeding on flowering plants contained more cytokinin than honeydew from vegetative plants.     

Ecdysone 20-Monooxygenase Activity of Cytochrome P450 in Ajuga reptans L. Plants and Cell Culture

The concentration of cytochrome P₄₅₀ and ecdysone 20-monooxygenase activity in plants and callus cell culture of carpet bugleweed Ajuga reptans L. were determined. The maximal ecdysone 20-monooxygenase activity of cytochrome P₄₅₀ was found in vegetative rosettes of intact plants. During the stage of flowering, the ecdysone 20-monooxygenase activity of cytochrome P₄₅₀ in plant leaves was higher than in other organs. It was demonstrated that the content of ecdysteroids in callus cell culture is higher than in the intact plant, with concurrent retention of a high ecdysone-20-monooxygenase activity.     

Experimental investigation on weather cues for mast seeding of Fagus crenata

Although a recent study has suggested that the minimum temperature from late April to mid-May in the year preceding flowering causes mast seeding in Fagus crenata, no direct evidence is available to support this finding. The aim of the present investigation was, therefore, to test – in a field experiment – whether the minimum temperature determines mast seeding in F. crenata. We examined the effect of nighttime temperatures on flower-bud initiation in F. crenata by enclosing fruit-bearing branches in heated bags at night, thereby maintaining average nighttime temperatures of approximately 2°C above the ambient temperatures. Heating was applied at night from 21 April to 20 May, 21 May to 19 June, and 21 April to 19 June in 2001. Female inflorescence initiation was inhibited by the nocturnal heating in the period 21 April to 20 May and 21 May to 19 June. However, nocturnal heating from 21 April to 20 May was the more important based on the odds ratio of the former being much lower than that of the latter in a logistic regression model. Male inflorescence initiation was also inhibited by nocturnal heating from 21 April to 20 May. We therefore conclude that flower-bud initiation in F. crenata was controlled by nighttime temperatures between 21 April and 20 May.     

Isolation of Flower-inducing and Flower-inhibitory Factors from Aphid Honeydew

The aphid Dactynotus ambrosiae Thomas has been allowed to feed on vegetative or flowering plants of the short-day plant Xanthium strumarium L., and the honeydew which they produce is extracted and tested for an effect on flowering using the long-day plant Lemna gibba L., strain G3 for the bioassay. One zone of flower-inducing activity and at least two zones of flower-inhibitory activity are consistently obtained from the honeydew extracts. The levels of flower-inducing and flower-inhibitory activity are not demonstrably different in vegetative and flowering honeydew. The honeydew extracts are inactive on Xanthium but do give some flower induction with the short-day plant Lemna perpusilla Torr., strain 6746. The flower-inducing activity is clearly of plant origin and is present in the phloem since the same active material can be obtained from vegetative or flowering Xanthium by methanol extraction, and honeydew produced by aphids feeding on a chemically defined synthetic diet is completely without flower-inducing activity. This is the first report of successful flower induction in the long-day plant L. gibba G3 by some means other than long-day treatment.     

Predictions of fate from rosette size in four “biennial” plant species: Verbascum thapsus,Oenothera biennis,Daucus carota,and Tragopogon dubius

Summary Individual plants were marked in field populations of four biennial plant species, Verbascum thapsus L., Oenothera biennis L., Daucus carota L., and Tragopogon dubius Scop., and followed for 2 or 3 years. The relationship of both rosette size and age to the probability of an individual dying, remaining vegetative, or flowering was determined for each species. In all four species, a minimum size must be reached before flowering can be induced and above that minimum the probability of flowering increases directly with rosette size. Conversely, the probability of dying decreases with increasing rosette size. In general, the fate of a rosette appears to be independent of its age although in populations where the probability of death is high for individuals above the minimum size for flowering, the age of a rosette may influence its fate to some extent.