Allogamy

As cross-pollination or Xenogamie is called in plants transfer of pollen from one flower to the stigma of a flower of another plant individual. Pollination as fertilization involving pollen is a part of the cross-pollination or allogamy. This includes not only flowering plants, but also plants without flowering, which multiply example on reproductive cells or spores, such as algae and ferns. In case of external fertilization, the genetic material of the mother plant and the father plant is recombined. The aim of the cross-pollination is to increase the likelihood of such a recombination of genetic material. Cross-pollination was discovered in 1790 by the theologian and botanist Christian Konrad Sprengel, among others, the narrow-leaved willow herb.

To be distinguished is the cross-pollination of the neighbor pollination ( geitonogamy ). In the neighbor pollination pollen is transferred from the flower of a plant to the stigma of a flower on the same plant. Neighboring pollination is therefore genetically equivalent to the self-pollination, as a distribution of genetic material and rearrangement will be omitted.

• 2.1 Vormännlichkeit
• 2.2 Vorweiblichkeit
• 2.3 Verschiedengriffeligkeit
• 2.4 Herkogamie
• 2.5 incompatibility
• 2.6 Training unisexual flowers tiger

Types of cross-pollination

Cross-pollination can be done by animals, wind, man and water.

Animal pollination

The animal pollination ( Zoogamie ) is further subdivided according to the type of pollinating animal. The area most frequently encountered animal pollination is by insects ( entomophily ). The insect pollination can continue to Fliegenblütigkeit ( Myophilie ) Bienenblütigkeit ( Melittophilie ) Tagfalterblütigkeit ( Psychophilie ) and more differentiated. In the tropics pollination by birds ( Ornitophilie ) and bats ( Chiropterophilie ) has an important meaning.

The means by which the plants attract their pollinators are diverse. Many insect- pollinated plants are pollinated by collecting nectar and / or pollen insects such as bees, bumble bees, butterflies and hoverflies. Lured these are usually produced by a large and lively colored perianth. Often, the bloom is designed dorsiventrally. Are nectar and scents available, one speaks of nectar flowers, missing this will be referred to the plant as a pollen flower. In adaptation to insect pollination stamens are often designed to be shorter and less divided the scars. Also with regard to the main pollinators, plants have developed specific adaptation features. Thus, the nectar in plants pollinated by butterflies is often the ground long tubes, while in plants that are mainly pollinated by flies, shallow nectaries dominate. Typical here is a characteristic fungal or carrion. Are moths the main pollinators, the flowers often open only in the evening. The flowers are usually colored inconspicuously, but have an intense fragrance.

Especially orchids have developed special mechanisms to attract pollinating insects. Some species have no nectar, but by imitating the form and color of the bloom flowers of other plants that provide nectar. Some species of orchids attract the males of certain species of insects to pheromones, causing them to copulation ( for example, the orchid species).

Kesselfallklamm flowers have, for example Aristolochia, Cypripedium and Arum. The special design of the flower get small insects in a cauldron-shaped extension of the flower or the spathe and Arum can exit this by devices such as Chartreuse hair again only when the pollination has occurred.

Flowers that are pollinated by birds, so-called bird flowers are often dyed bright red color, because insects can not see this color.

While the animals collect the nectar, they are a dusting of pollen. They fly to the next flower, the pollen sticks to their scar.

Wind pollination

In the wind -pollination ( Anemogamie ) the pollen is carried by wind and fall by chance on the stigma of another flower.

Wind -pollinated plants often have inconspicuous or completely missing blossoms cases. Nectar and fragrances are not produced. The flowers are often together in many-flowered, often unisexual inflorescences. The abundant pollen is produced in often long and moving in the wind stamens. Pollenkitt is usually absent. The scars are formed large and strongly divided.

Typical Windbestäuber are the grasses, wheat, rye and corn. The pollen windbestäubender plants can cause hay fever.

Water pollination

The rare water pollination ( hydrophilicity or Hydrogamie ) occurs in some plants that grow submerged or on the water surface. Pollen can be transported above or below the water surface.

Mechanisms to promote cross-pollination

In many plant species, devices have developed to prevent self- pollination of the flowers. The most common are:

Vormännlichkeit

When Vormännlichkeit ( Proterandrie ) the anthers empty the pollen before the stigma of the same flower is ready to conceive. This occurs in the composite flowers, the sage, the bellflower and the corn for example.

Vorweiblichkeit

When Vorweiblichkeit ( Proterogynie ) the scar is already ready to conceive for some time before emptying the dust bag. During this time, the scar can only be pollinated by pollen from other flowers, thus increasing the probability of cross-pollination. The Vorweiblichkeit comes, for example, before the plantain.

Verschiedengriffeligkeit

In some plant species, there are individuals in whom the pen are long and the anthers deep-seated, and individuals, in which the stylus is short and the anthers sitting high. There are thus two different types of flowers. This is called Verschiedengriffeligkeit or heterostyly. In other species with two stamen circles there are even three different types of flowers, depending on whether the stylus on the bottom, the middle or the upper level are ( Tristylie ).

Fertilization takes place only if the pollen comes from a plane to a scar same plane. For example, pollen must move from short stamens and the stigma of a short pen. But this can not happen within a flower.

Examples are the primrose with two levels, or purple loosestrife and the sorrel plants in which Tristylie occurs.

Herkogamie

The stamens of a flower and scars are spatially separated in this. An example is the iris.

Incompatibility

Cross-pollination is also promoted by a physiologically induced incompatibility between scar tissue and pollen or stylus and pollen from the same individual.

Training unisexual flowers tiger

Monoecious or dioecious distributed unisexual flowers also support cross-pollination. In Einhäusigkeit male and female flowers are present on a plant specimen. When the flowers dioecious distributed exist male and female individuals. Consequently, the single individual has only male or female flowers. This group of plants belonging to the buckthorn, the willow or the Dog's Mercury. Since male and female flowers are distributed to different individuals, self-pollination is excluded.

Function of cross-pollination

Pollination supports the genetic diversity of a species, since genotypes are mixed with different alleles during fertilization. Result, the probability is reduced that adverse recessive alleles come together as a couple in an organism and so the harmful properties in the phenotype is expressed. Through cross-pollination, the number of genetic combinations is increased within a population. If, for example, changes in environmental conditions to which it is more likely that at least some copies of the population can adapt to the new conditions successfully. Cross-pollination can also lead to the emergence of hybrids that can be more vital than the respective parent plants in their properties.

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