Many people know that cross-pollination is one of the most common ways of propagating plants. But the information about why most plants chose this method, as well as about various types, is not so common.
What it is
Pollination is the process of transferring pollen from anthers to the ovule (common among gymnosperms) or the stigma of a pestle (inherent in angiosperms). As a result of this, a female organ - a kidney or ovule - begins to develop, being transformed into a fetus.
There are two most common types of pollination - self-pollination and cross. The first option is less common. In this case, pollen falls from the anther on the pistil of the same flower, often even before its petals open. On the one hand, it is much more reliable - the number of empty flowers in this case tends to zero.
Cross-pollination is the process of transferring pollen from the anther of one flower to the pistil of another. And this option, despite the great complexity, is found among plants much more often - in almost 90 percent of higher plants. Why is cross-pollination common in nature?
Types of Cross-Pollination
To date, experts have identified two types of cross-pollination in plants — xenogamy and geytonogamy.
Heytonogamy is the pollination process in which the stamens and pestle of different flowers, located on the same plant, are involved. That is, the tree is quite capable of self-pollinating and bearing fruit even in the absence of relatives nearby.
Therefore, experts have long been debating whether this is cross-pollination or, rather, there is a special way of self-pollination. The fact is that there is no exchange of genetic material here, namely it is the main goal of cross-pollination.
But xenogamy is a completely different matter. The process goes exactly the same, however, flowers located on different plants should be involved in it. In order to protect against accidental pollination of flowers on the same plant, some species even developed a protective mechanism - the separation of the sexes. Moreover, in the flowers of one plant there are only pistils, and on the other - exclusively stamens. Therefore, the probability of self-pollination is completely eliminated.
Who helps pollination
Of course, the main assistant in cross-pollination is insects, primarily bees. Zoophilia takes place here - this is the term that refers to any pollination of plants carried out with the help of representatives of the animal world.
Two rather rare subspecies can be distinguished here:
- myrmecophilia, when pollination is carried out exclusively by ants;
- cantarophilia - here the beetles act as the main pollinators.
But this is found only in relict plants that have survived to the present.
Another case of bestiality is ornithophilia - pollination by birds. Such cross- pollination of plants is not very common - it occurs mainly in the tropical zones of America, because the only birds that contribute to pollination are hummingbirds.
Finally, chiropterophilia is quite common - pollination by bats. And plants using this method are also common only in warm countries, mainly in the jungle. Bats, licking the sweet nectar from the flowers, carry pollen on the tongue and wool.
Less common are anemophilia (pollination by wind) and hydrophilia (here pollen is transferred from flower to flower by water - it is found in some gymnosperms and algae).
Now it is clear that pollination can be carried out by a variety of methods. But which one is the most common?
The prevalence of different pollination methods
The lion's share of plants that use cross-pollination do this with the help of bestiality. Yes, it is insects, birds, or mammals that pollinate nearly 80 percent of higher plants.
Significantly behind the leader of anemophilia. No more than 20 percent of plants use wind to carry pollen.
But the least common hydrophilia. Less than 1 percent of all plants trust pollen transfer to water streams - in ponds or after rain.
Main advantages
It is worthwhile to understand why cross-pollination is so common.
As noted above, the number of barren flowers is almost completely absent in plants using self-pollination. But at the same time, it was cross-pollination that turned out to be more viable - this proves the abundance of such plants.
In fact, everything is simple here. With self-pollination (as with geytonogamy), the plant multiplies by itself. Only the genetic material that it has is used and, as it turned out, this is a losing strategy.
Indeed, with xenogamy, plants that grow from seeds obtained by crossing two plants receive the advantages and characteristics of both parents. That is, if one tree grew on arid soil and managed to adapt to it, and the other, on the contrary, grew on a swamp and survived, then the new tree, which became their offspring, will equally easily adapt to a lack of moisture, and to its excess. Consequently, the likelihood that it will die under adverse conditions is sharply reduced.
It is because of this that cross-pollination plants began to dominate all over the world, confidently crowding out competitors that appeared on Earth millions of years earlier.
Ways to attract pollinators
It was noted above that four out of five plants are used for pollination of animals - from mammals to insects. Of course, at the same time they developed an appropriate mechanism for their lure.
The most common is the presence of sweet nectar. Many millions of years ago, trying to attract pollinators to themselves, some plants acquired cells capable of secreting a sweet substance. The experiment turned out to be successful, and as a result, he had many thousands of descendants who produced nectar with a pungent odor. Such plants are primarily oriented to animals and insects with a delicate sense of smell.
But there are plants that use ornithophilia. And the birds, as you know, are almost devoid of smell. A different trick was used here - larger and brighter flowers that hardly smell. They perfectly attract hummingbirds, who know that sweet nectar awaits them inside.
Conclusion
From this article it becomes clear what cross-pollination is, as well as what are the main advantages of this method. And at the same time, the article gives information about different pollination methods involving various external forces. This will make it possible to better understand botany and become known as a person with the broadest horizons.