The transfer of pollen grains from the anther of a stamen to the receptive part of a carpel, the stigma is known as pollination. In most cases, the agency by which the pollen is transferred, is one of two kinds, by insects, or by wind. Flowers are said to be entomophilous if insects are the agents of pollination while they are said to be anemophilous if the agent of pollination is wind. Entomophilous flowers generally have the following characteristic features:
- They are large, brightly colored and often scented. If small, they are aggregated in numbers to form a broad expanse of color against the background. Insects are thus attracted visually and sometimes through the alfactory sense over some distance.
- The flowers provide a source of food for insects which imbibe sugary nectar from the nectarines or collect the pollen, or both.
- Nectaries, anthers and stigmas are situated in a special relationship to one another, so that the anthers and stigmas must be disturbed if the nectar or pollen is to be reached by the insect, i.e. there may be highly specialized pollination mechanisms in the flower, e.g early purple orchis.
- The pollen grains of entomophilous flowers are usually thick-walled, sticky and spiny to enhance adhesion to insect bodies.
By whatever agency pollen may be transported, there are two distinct possibilities with reference to its eventual destinations. First, the pollen may be transferred from an anther to a stigma in the same flower or in another flower on the same plant. Secondly, the pollen may be transferred from an anther in a flower on one plant to a stigma in a flower on another plant of the same species. The former constitutes self –pollination while the latter is referred to as cross-pollination.
If gametic union is effected between male and female gametes produced by the same plant, the mixture is less likely to lead to variation than if the gametes of different plants unite. In other words, cross-pollination is a more effective method of producing new variants than self-pollination. Hybridization by plant breeders is effected by controlled cross-pollination, in which pollen is actually transferred from one plant to another by a brush.
The Pollination Process of Entomophilous Flowers
Splachnacea flowers have appendices and nectaries that function as pollination mechanisms. These structures attract insect visitors to the plant. Fly visitors bend over the staminate or pistillate flower, lowering their heads towards the anthers and extending their proboscises.
This pollination process is known as entomophily. Entomophilous flowers advertise themselves with bright colors and produce good odors.
Self-Pollination in Entomophilous Flowers
Unlike most plants, which require a pollinator for successful fertilization, entomophilous flowers can self-pollinate. This is possible because the pollen grains of these flowers are thick-walled and sticky to enhance adhesion to insect bodies. These grains may be transported from an anther to a stigma on the same flower, or from one flower to another of the same species. This is called cross-pollination, while the former is referred to as autonomous selfing.
This mechanism of autonomous selfing allows the plant to survive in habitats where pollinator populations are limited. It also provides a backup mechanism to ensure reproductive success when other pollination mechanisms fail. In the case of the endemic tree Boswellia ovalifoliolata, the mechanism is facilitated by a combination of floral traits and natural pollinators. Specifically, the bud and flower feeding of Weevils and Sunbirds have been found to influence pollination. In addition, the Garden Lizard has been observed to lie in wait closely to flowers and suck nectar through its curved beak.
These specialized flowers are shaped and coloured to attract specific insects and facilitate their transfer of pollen grains. The flowers of the solitary orchid Ophrys apifera, for example, mimic the female sex pheromone of a specific solitary bee species. In addition, entomophilous flowers often have sticky stigmas that attract pollinators and help to ensure successful fertilization.
Nevertheless, the effectiveness of pollinator-supported selfing will vary enormously between different habitats and among closely related species, as a result of differences in the nature and quantity of floral rewards, movement of pollinators, time spent on individual flowers, and floral biology. Moreover, it is important to note that the morphological adaptations that promote autonomous selfing may also reduce attractiveness to other pollinators.
In order to test the effects of morphological traits on the ability of entomophilous flowers to support self-pollination, we examined the performance of three short-living Centaurium species (Centaurium erythraea, C. littorale, and C. pulchellum) in coastal dune areas of Western Europe. For each of these species, a sample of flowers was subjected to either natural or artificial selfing by removing anthers prior to flower opening. Seed set was then assessed in treated and control flowers after fruit maturation. The results showed that anther removal reduced the rate of self-pollination in C. erythraea by more than 50%.
Cross-Pollination in Entomophilous Flowers
The transfer of pollen grains from the anther of one flower to the stigma of another different plant is called cross-pollination. This process is essential for the production of new variants in plants. It also allows hybridisation, a key step in the process of producing cultivated crops. Cross-pollination is generally facilitated by external agents, such as wind, animals and insects. Anemophily by wind, zoophily by animals and entomophily by insects are common examples of cross-pollination.
The flowers of entomophilous plants are brightly coloured, fragrant and nectar-producing. They are also sticky and spiny to enhance adhesion to insect bodies. These features attract bumblebees, wild bees, honey bees, ants, midges and moths. Some garden flowers and wild plants are entomophilous, including lily of the valley, tulips and dandelions. Other plants, such as roses and orchids, are entomophilous by default, as are many monocot grasses such as maize and jowar.
Most flowering plants are unable to reproduce by themselves and depend on animals for pollination. To ensure that this process is successful, the flowers are often shaped to match the body shape of the pollinating animal and scented to mimic its pheromones. They may also have structural modifications that allow them to trap the pollinators until they release the pollen.
Some flowers are protandrous, meaning that the stamens ripen before the pistils. In contrast, some flowers are gynodioecious, where the stamens and pistils mature at the same time. This is a common feature of roses and avocados.
If the anther and stigma of two different flowers unite, fertilization takes place and a seed is formed. Cross-pollination is a more effective method of reproduction than self-pollination, because it results in the transfer of the hereditary traits of both parents to the offspring. However, self-pollination is not foolproof and can result in a genetic mutation that is detrimental to the plant. It is also less effective in a changing environment, where the offspring of outcrossed plants may be better adapted to the new conditions than those resulting from inbreeding. In addition to cross-pollination, the process of hybridizing is another important means of creating new varieties of flowers.
Insect pollination is a type of pollination in which insects carry pollen from the anthers of one flower to the stigma of another. The flowers of entomophilous plants have features designed to attract insects, such as bright colours and a sweet scent. They also have glands that produce nectar, a reward for pollinators. Bees, butterflies, moths, flies, and beetles are common insect pollinators. Insect-pollinated flowers are usually hermaphrodites, and the ovules of female flowers contain seeds. Insect-fertile flowers have large stamens and a sticky pollen, which make them easy to transfer to the stigma of other flowers.
In order to facilitate this process, entomophilous flowers advertise themselves by offering rich rewards like sugary nectar. They often have patterns (known as nectar guides) that guide pollinators to the nectaries and lead to cross-pollination. Flowers may also have an attractive odor, mimicking the pheromones released by predatory insects.
Traditional classifications of flowering plant morphologies include those that depend on insect pollination, those that depend on wind (anemophily), and those that do not have either. These classifications are based on features such as nectar production and distribution, floral rewards, and flowering time. Despite their limitations, these classifications are useful for comparing evolutionary relationships.
Many plants, such as grasses and birch trees, are primarily anemophilous. These plants do not have the resources to attract insects, so they rely on the wind to move pollen from flower to flower. This is a much less efficient method of pollination than the method used by entomophilous plants.
Insect-pollinated flowers have adapted to the needs of their pollinators by changing the structural characteristics of the petals and modifying their coloration. They also produce thick nectar that can be easily transferred between flowers. This is because insects are more likely to eat dense nectar than watery syrups.
Insects are essential for the reproduction of flowers. They are responsible for the dazzling displays of beauty that we admire in nature. They inspire poetry, music, and art and bring joy to children’s play. Their work ethic is even celebrated in the clothing industry; iridescent beetle wings were sewn into the finest Victorian dresses before synthetic sequins were invented. Besides the aesthetic benefits of pollinators, they provide economic and environmental services to humans. They increase seed production and quality, change the composition of microbial communities in seeds, and even help to create agroecosystems that are resistant to environmental pressures.
The pollination of flowers is a crucial process for plant reproduction. A gardener can obstruct this process by using pesticides, which kill helpful insects that spread pollen from flower to flower. Additionally, wind and rain may impede pollination by disrupting the morphology of the flower and degrading its ability to attract pollinators. Another important factor in pollination is the amount of nectar a flower produces. If a flower is not producing enough, it cannot attract pollinators and will not be able to cross-pollinate. This can be a problem for plants such as orchids and anthuriums, which require large amounts of nectar to thrive.
Entomophilous flowers are typically vividly coloured and fragrant, and secrete nectar to attract insects. These plants also produce special structures that allow them to transfer pollen between flowers. These structures include long anther tubes that extend from the pollen sacs and are able to capture airborne spores. These spores are the seeds from which new flowers will form. These spores are transferred from the stigma to the ovary, where they will develop into pollen grains.
Pollen transfer between different flowers can be affected by various factors, including floral morphology and bee species. The ratio of dye particles to pollen grains on a stigma is a good indicator of the level of pollination. However, the rate of pollen decay on a stigma is slower than that of dye particles. The result is that the number of dye particles on a stigma is often higher than the number of pollen grains.
This study examined the effects of bee species and donor and recipient floral morphology on mean pollen transfer and the slope of pollen transfer across a sequence of flowers. The analysis included ANCOVA models with bee species and flower sequence as main effects and a two-way interaction between bee species and flower sequence. The results show that floral morphology did not influence mean pollen transfer, but the slope of pollen transfer was more sensitive to bee species than flower sequence.
Stigmas were collected by forceps into individual 1*5-ml plastic microcentrifuge tubes after bee visits and immediately cleaned in ethanol to avoid contamination. Dye particles were deposited on the stigmas with similar consistency to pollen grains, so they served as a good pollen analogue. Nevertheless, low numbers of dye particles were found on bagged control stigmas, suggesting that either some pollen was not successfully cleaned from bees before trials began or that the bagged stigmas received unsuspected pollen from other sources.