In spring, the season of blooming flowers, the flowers have embellished people's living environment with their own gorgeous and colorful images. With them, the world around us blooms with countless colors.
Why should the flowers show their beauty in the spring? In fact, they only have one wish, that is, to attract pollinators, and to ask these "love messengers" of nature to transport pollen to the pistil stigma of other plants to complete the annual vital "life event".
For a time, a good bee is busy, butterflies are drunk, you chase me to catch up with the flowers, the brakes are lively! At this moment, "attracting bees and attracting butterflies" has become a beautiful time for plants to be extremely happy.
The structure of the flowers
Plant flowers, which bear the function of producing seeds to reproduce offspring, are composed of male organs, female organs, petals, calyxes and flower holders, and peduncles. Male organs refer to groups of stamens composed of anthers and filaments whose function is to produce pollen. The female organ refers to the pistil group composed of three parts: ovary, flower pillar and stigma, and the ovules in the ovary are powdered before they can develop into seeds. The petals (corolla) and the constituent quilts surround the male and female organs, and their common goal is to attract insects to come and collect honey in order to achieve the beautiful goal of breeding offspring.
One of the important ways for plant flowers to attract insects is to secrete the food --- nectar needed by insects. Nectar comes from the nectar glands of the flowers themselves, which are formed by the nutrients absorbed by plants from the soil and photosynthesis, and the nectar is stored in addition to meeting the needs of its own growth and development.
During the flowering season, these nutrients are delivered to the flowers, some of which are used to form fruits and seeds. The other part is converted into honey juice, which is stored in honey gland cells. In order to achieve the reproductive mission of plants, honey gland cells will use these nutrients, under suitable conditions, secreted through the epidermis of the honey glands to the outside of the body, attracting insects to come and collect honey.
There are some inconspicuous lines on the petals, which we call "honey marks". Don't underestimate these lines, a day or two after flowering, insects will smell the incense and follow these lines to find nectar on the flowers.
When the stigma in the flower has matured, it is time to start accepting pollen. At this time, when the insects come to collect honey, they will inadvertently crawl over the anthers, and the whole body will be covered with pollen. And these pollens on their bodies may be brought to the stigma at this moment. These lucky pollens were thus involved in the cultivation of plant seeds.
Plant pollination can be divided into two types: some plant pollen can germinate on its own stigma, which is called "self-pollination"; most plants need to accept the pollen of another plant of the same species to be able to complete the pollination work, which is "cross-pollination".
When the pollen falls on the stigma of the flower of the same plant, a pollen tube grows, and the pollen tube will follow the stigma, through the peduncle, to the ovary, so that the ovules can be fertilized. There are two male cells in the pollen grain, one of which binds to the egg cells in the ovule, dividing to form the embryo of the plant. The other binds to two other cells in the ovule to form endosperm. Endosperm stores the nutrients needed for embryo growth. The embryo, together with the endosperm and seed coat, forms the seed of the plant.
However, some of the plant fruits we see are not actually seeds, but are developed from protecting seeds. For example, the apple, its sweet and delicious fleshy part is not a seed, but is formed by the development of the original ovary, which is used to protect the real seed, that is, the core part. In addition, the fruit also has the function of helping to sow seeds, because the brightly colored, sweet and juicy fruit often attracts animals to come and feed, so that their offspring go in all directions.
The function of flowers
In the relationship between plants and flowers and animals, the reason why plants use their graceful flowers to cater to the different preferences of animals is quite clear. But in the face of colorful and fragrant flowers, do you know what insects like when they collect honey?
Insects often have some special hobbies during the honey harvesting process, especially when they visit the flowers of the same plant and turn a blind eye to other plants and flowers around them. This hobby is conducive to ensuring that the same plant reproduces its own pure offspring through different pollinations between each other. So how do plants make insects indifferent to the flower world outside? And how to ensure that the taste of insects is single-minded, so as to achieve the purpose of fixing the main characteristics of the plant population?
In the case of bees, when different forms of flowers are distributed in different areas, bees will continue to choose one flower to collect honey. But it would be bad if the different forms of flowers were evenly dispersed to the same area, and the bees might be lazy and become less picky. Of course, bees tend to have 4-5 seconds to think about it before making a choice. If a bee finds the same flowers during this time period, it will definitely choose those same flowers.
Bees also have their own memory effect, bees and bumblebees have strong learning ability, they will use the previous experience of collecting nectar to follow up work. However, even with the accumulation of work experience, sometimes it is inevitable to be a little lazy. Therefore, in order to "do what they like", the same variety of plants bloom in large areas.
Butterfly pollination (photo by the author)
Photo by Shanghai Entomological Museum
The contribution of color
Why do flowers have countless strange and brilliant colors? Darwin's theory of natural selection explains it this way: Insect activity plays a rather important role in this, because hundreds of millions of years ago, gymnosperms just appeared on the earth, and insects were not very numerous. The color of the flowers is also relatively plain, and at that time, the plants were basically pollinated by the wind, so these plants were called "wind flowers".
Later, quilt plants appeared, and insect species also increased. The flowers of angiosperms are more differentiated into calyxes and corolla (collectively known as indumentum). The petals are no longer only green, but more conspicuous yellow, white and other colors appear. The shape has also begun to grow larger, some have grown honey glands to secrete honey juice, some can emit fragrance, these plants that rely on "color to lure" insects to pollinate, is today's so-called "insect-borne flowers". It is precisely because of the "bee fighting for the fragrance of the butterfly", today's insects have gradually become the main force of pollination and insemination of flowers in the plant kingdom.
It is conceivable that if there was a plant with a reddish flower color, which must be very conspicuous under a green background, and it is easy to attract the attention of insects, then it has more chances of pollination. Over the course of time, these plants have reinforced this advantage until their offspring have evolved to form pure, prominent, bright red flowers. It can be said that it is precisely because of the natural selection involving insects that various plants with different forms have been formed, and colorful flowers have been created.
You know, different animals have different preferences for color: birds are more sensitive to red, bees are fond of yellow and blue flowers, and moths prefer white. It can be seen that the reason why flowers can release specific color signals for pollinators has a considerable relationship with the desire of plants to attract the vision of different animals.
The credit of the fragrance
From the perspective of physiological needs: the aroma of flowers is not just for people to revel in, but a smell "language" for insects to help pollinate, so the floral fragrance is also called "xeno pheromones". In addition, the diffusion of the aromatic oil in the flower can also reduce the evaporation of water on the petals, so that it will not wither due to the sun, or freeze due to cold. From the material basis, most of the petals that emit aroma have an oil cell that can secrete a strong fragrance of aromatic oil, which is easily volatile and brings aromatic oil. Of course, there are also some floral fragrances that do not produce aromatic oils, but because there is a sugar ligand body in the flower, the sugar ligand body is decomposed and can also emit aroma.
Not only that, but sometimes some plants even try to cater to the small hobbies of some pollinators, so that they maintain a specificity with themselves in the pollination work. For example, the yellow plum is prepared for the bees that like to smell sweet (that is the unique taste of ester compounds). Although this method seems a bit crude, it is largely enough to ensure the quality of the pollen delivered.
Before the harvest season of the plants, the flowers invite the animals to come with the help of colorful colors and fragrant smells, and the animals also obtain a harvest through their own hard work in the process of helping the plants to complete the mission of population continuation, which is a win-win situation for the talents of nature.
This article was published in Science 24 Hours 2018.4, and has been revised here.
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