Corolla wilting facilitates delayed autonomous self-pollination in Pedicularis dunniana (Orobanchaceae)

Structural changes associated with corolla wilting may serve as a mechanism for effecting self-pollination. Low pollinator visitation, high seed production and a corolla that persists after anthesis indicates that Pedicularis dunniana is autogamous. Delayed autonomous self-pollination is facilitated by corolla wilting. Wilting of the upper lip (galea) brought the pollen laden anthers into contact with the stigma resulting in the deposition of self pollen on the stigma. The seed set of flowers either emasculated, or with restrained galeae thus preventing anthers brushing against the stigma, was significantly lower than that of open-pollinated flowers. This demonstrates that autogamy occurs in this species through corolla wilting. Germination experiments indicated that outcross seedlings were more vigorous than selfed seedlings as a result of inbreeding depression. It is likely that autogamy provides reproductive assurance for P. dunniana under conditions of pollinator scarcity.     

Rates of corolla growth in tobacco determined with the plastochron index

The growth of vegetative and reproductive shoots of Nicotiana tabacum L. cv. Xanthi is analyzed with the plastochron index to estimate the relationship between corolla growth and time. The plastochron of leaves 9 through 20 declines steadily at each successive node. The flower plastochron increases steadily during the growth of an individual cyme, with the most distal flower to open having the longest plastochron. Variation in the flower plastochron is the result of variation in the rate of flower initiation, not the growth rate of individual flowers. The corolla has an extended phase of approximately constant relative growth in length (between 0.2 · d^–1 and 0.3 · d^–1) until a peak of growth (0.5 · d^–1) 2–3 d before anthesis. Corollas also have periodic peaks and troughs of growth that are low in amplitude (0.1 · d^–1), but persist throughout most of corolla development. The pattern of corolla expansion contrasts strongly with earlier reports of the pattern of tobacco leaf growth.Abbreviations PI plastochron index - PR plastochron ratio - RGR relative growth rate in length The authors thank: Drs. T. Sage and E.G. Williams for the considerable time and space they invested; the members of Dr. R. Wyatt's laboratory for allowing us to use their computer facilities; A. Tull and M. Smith for their care taken in the green-house. This research was supported by U.S. Department of Agriculture grant GAM-89-01056 and by National Science Foundation grant DCB-87-15799.     

Size-related selection of food plants by bumblebees

Abstract. 1. A positive correlation between the tongue length of conspecific workers collecting nectar from seven plant species and the corolla length of the flowers probed was found for B.lapidarius and B.pascuomm but not B.terrestris . No simple relationship was found between the volume, sugar weight or concentration of nectar in flowers and the tongue or wing length of probing bees.
2. B.terrestris workers collecting pollen from four plant species producing pollen only, were found to differ in size according to the type of pollen presentation mechanism and the pollen content per flower. Body size variation was also related to the foraging of pollen plus nectar from two other plant species.     

Pollen morphology in the genus Veronica L. (Plantaginaceae) and its systematic significance

Pollen grains of 30, mainly annual, species from 134 populations of the genus Veronica (Plantaginaceae, formerly Scrophulariaceae) from the Mediterranean Region, have been studied with light and scanning electron microscopy. Three pollen types are defined based on pollen size and exine surface sculpture. In some cases within the study group pollen size can be useful in species determination. Hypothetical relationships of pollen grain size and aperture number with ploidy level, style length and corolla diameter are discussed. The ornamentation of the exine in Veronica, although generally a conservative character within the genus, gives some additional support to the most recent infrageneric classification of Veronica.     

花冠对紫茉莉繁殖适合度的影响

以授粉后具花闭合特性的紫茉莉为研究材料,通过在不同天气状况下作去花冠和存留花冠处理,观察花冠对花粉活力、柱头可授性及结实率等繁殖特性的影响。结果表明:紫茉莉自然存留花冠比去花冠的花粉活力、柱头可授性、柱头上的花粉数及柱头上花粉萌发率各指标达最高值的时间重叠性更强,并以阴天存留花冠的最强。存留花冠通过这种时间的重叠性来保证花粉在柱头上的萌发,产生了有利的繁殖适合度。越晚去花冠结实率越高,结实率呈现花闭合自然存留花冠>花冠闭合期去花冠>散粉初期去花冠>花冠展开期去花冠的规律。因此,花冠对紫茉莉繁殖适合度具有利影响。紫茉莉花冠的存留提高了繁殖适合度,增强了对环境的适应能力。     

秦岭石蝴蝶人工种群花器变异现象研究

以人工栽培的秦岭石蝴蝶为实验材料,通过观察并记录花器官形态和数目的变化,初步探讨秦岭石蝴蝶花器变异规律,并分析了导致其变异的诱因。结果显示:(1)在观察的1 996朵秦岭石蝴蝶花朵中,发现了17种花冠变异类型、5种萼片变异类型和7种可育雄蕊变异类型,总变异率分别为34.57%、38.38%和32.67%。(2)秦岭石蝴蝶花梗或可分支,花梗苞片数目2～3枚。(3)相关性分析结果表明,下唇数目与可育雄蕊数目呈正相关,相关系数为0.927 4,而上唇数目与可育雄蕊数目呈负相关,相关系数为-0.481 1,结合花型图示分析这可能与秦岭石蝴蝶雄蕊着生于花冠下唇内侧近基部有关。该研究统计的秦岭石蝴蝶变异类型丰富,可能对于今后秦岭石蝴蝶的系统进化、花器官发育、生殖生态以及分子遗传方面研究奠定了基础,也为培育不同观赏价值的品种提供思路。     

The cooling of convolvulaceous flowers in a tropical environment

The temperatures of flowers of Ipomoea pes‐caprae ssp. brasilensis, Ipomoea aquatica and Merremia borneensis in bright sunshine, were studied to determine the role of corollas and sepals in cooling the gynoecium. The corollas and sepals were prevented from transpiring by greasing, to investigate the extent of evaporative cooling. In the exposed natural habitats of these flowers the maximum temperatures of air and soil were high (32 and 42 °C, respectively) and corolla, sepal and gynoecium temperatures were often intermediate. Despite being almost astomatous, significant evaporative cooling was observed in the corolla. Between 20 and 80% of the energy absorbed by the corollas was dissipated as evaporation. The sepals were stomatous and their evaporative cooling was very important in reducing the temperature of the gynoecium. The temperatures of the non‐transpiring gynoecia and corollas were significantly higher than the temperatures of the normally transpiring corollas and gynoecia. Furthermore, the gynoecia temperatures were significantly higher with non‐transpiring corollas than with normally transpiring corollas, suggesting that the corollas alone play a role in maintaining the gynoecium within optimal temperatures levels. It was shown in an incubation experiment that temperatures exceeding 32 °C may damage the carpels, and temperatures exceeding 42 °C may damage sepals. Pollen grains were killed after 200 min of exposure to temperatures in the range 32 to 47 °C. It is concluded that the cooling mechanisms (evaporation and self‐shading) are critical for the reproductive success of these flowers in their natural environment.     

Are Nectar Sugar Composition and Corolla Tube Length Related to the Diversity of Insects that Visit Asteraceae Flowers?

Abstract: In this work, we analysed interspecific variation in nectar sugar composition, corolla tube length, and the diversity of floral visitors of 35 Asteraceae species. The potential correlations between these variables could arise either as a result of selection to improve pollinator attractiveness or simply as a consequence of phylogenetic constraints. Samples of nectar and flowers, and data on floral visitors, were obtained from living plants in natural populations from Argentina. Asteraceae species showed a large variability in corolla tube length. Nectar of most species presented a larger proportion of hexoses than sucrose. All species were visited by numerous insects belonging to 2 different orders. Results showed that floral traits are not significantly correlated with the diversity of floral visitors. These characters seem to be linked to the phylogeny of the species. Early branching species (species phylogenetically close to the root of the Asteraceae tree) tend to have longer corollas, higher sucrose proportions and lesser diversity of floral visitors than late branching species. Considering that longer corolla tubes and higher nectar sucrose percentages may indicate some specialization in the pollination system, we suggest that there is an evolutionary tendency toward generalist pollination systems within the family.