The end of the Mesozoic and Cretaceous period of development of the planet's biomass is characterized by the dominance and wide distribution of a new branch of algae evolution - angiosperms, or flowering plants. The reasons for this phenomenon were the special devices available in the arsenal of the structure of this group.
Today, the flowers, seeds and fruits that they produce are not only an important link in the food chain of most biogeocenoses, but also a source of nutrition for people, medicinal raw materials, household material, and so on. Over 250 thousand angiosperms are known, which exist in a variety of life forms (trees, vines, grasses, shrubs) and inhabit almost all parts of the world, continents and continents.
Classification of Angiosperms
The organ of seed reproduction in flowering plants is the flower itself. It is by its structure, appearance, and also by a number of other morphological characters that the entire department of Angiosperms is divided into 2 main classes:
- Monocotyledonous plants. There are about 63 thousand species united in 122 families. Also, the class consists of 3 thousand births. The most common families: Cereal, Liliaceae, Ovoid, Palm, Orchidaceae, Sedge, Bromeliad, Water Lily, Pepper and others.
- Dicotyledonous. More than 190 thousand species, united in 10,000 genera and 418 families. The most common of the latter: Cruciferous, Rosaceae, Myrtle, Grape, Moth or Legumes, Solanaceae, Umbrella and others.
The main differences between these classes are the structure of flowers, root system, leaves. The economic importance of all these plants is very great (vegetable and fruit crops, textile production, building materials and dyes, medicines, etc.), as well as the role in nature.
Evolutionary structural innovations
There are several of them. These are exactly the signs that allowed Angiosperms to spread so widely on the planet, to be so hardy and adapted to habitats and climatic environmental conditions.
- The organ of seed reproduction in flowering plants is a flower and a fruit formed after it. The seed is protected, covered with the pulp of the fruit or hard skin, which gives a great advantage in the survival of species and their distribution.
- A variety of vegetative methods of reproduction.
- Numerous types of pollination.
- Adaptation of the internal structure to difficult environmental conditions (drought, excessive humidity, bright sun or lack thereof, frost and so on). This is an advanced conductive system, flowers, seeds, fruits, powerful rhizomes and so on.
- A variety of life forms.
- Propagation of flowering does not depend on the availability of water.
All these features allowed these plants to populate land everywhere and become leaders among representatives of the flora.
Reproductive organ flowering
The organ of seed propagation in flowering plants is the flower, then the fruit covering the developing seed. The structural features of the flower, its peculiar structural parts, methods of pollination and development - all this makes angiosperms unique champions among plants in reproductive function.
For a man, a flower is an aesthetic perfection that you can admire, give and delight others, inhale its pleasant aroma. However, the significance in nature of this structure is quite obvious - it is an organ of seed reproduction in flowering plants. Functional significance is determined by the processes of fertilization and development of sporophyte from the seed.
Flower structure
The flower and fruit of any representative of angiosperms in its structure is ingeniously thought out and organic. The combination of all parts allows the plant to carry out reproductive functions in full, regardless of climate and other abiotic environmental factors.
Consider the general features of the structure of the flower.
1. Stem part:
2. The sheet component. It is formed by sepals (most often green) and the petals forming the corolla. Its color can be very different, from white to dark purple.
3. The generative part. Reproductive organs that provide for the reproduction of flowering. These are pistils, stamens, ovary.
Outside, the main generative components are delimited and protected by the perianth. This structure includes:
- a cup of sepals;
- whisk from painted petals.
Perianth can be simple or double, depending on the type of plant. It contains a large number of different substances: essential oils, pigments (carotenoids, xanthophylls, chlorophyll, anthocyanins, anthofeins and others). It is because of this that the flower exudes a scent that attracts pollinators. Corolla has various sizes and colors, which is also important for the attraction of insects, birds, animals.
The direct organ of reproduction of the flowering plant consists of gynoecium and androecium, which are under the cover of the perianth. Androecium is the totality of all stamens that perform the function of the male reproductive organ. The structure of the stamen is simple, represented by the following structures:
- stamen thread;
- anther of two halves connected by a binder;
- microsporangia are nests inside the anther in which the process of microsporogenesis and microgametogenesis (the formation of sperm and microspores) is carried out.
Through the stamen filament, the anther binds to the peduncle, the exchange of nutrients and metabolic products. The resulting microspores further form the male sporophyte. Sperm lead to the formation of dust particles, which will participate in fertilization and seed formation.
The gynoecium of the flower is formed by the totality of all the pistils included in its composition. This structure is important because it is, as already mentioned, a female reproductive organ. Pestle consists of:
The ovary is the structure that forms the widest part of the pestle. It is formed from the inside by the ovules, which take part in the formation of the pericarp. Within these structures, the processes of megasporogenesis and megametogenesis occur. Also in the ovary, the process of fertilization and seed formation, its development.
The pestle column can be of different sizes. It serves as a bond between stigma and ovary. It is distinguished by sterility, that is, it does not take part in the sexual process.
The stigma of the pistil serves to capture the dust particles that fall from the stamen anthers. The size and shape of these parts is different, depending on the type of pollination of the plant.
Flowering plants: propagation
A flower may contain a different number of pistils and stamens. There are species in which only stamens or only pistils are present - they are called male and female, respectively.
What else are interesting flowering plants? Reproduction in them can be both sexual and asexual, i.e. vegetative. We are talking about sexual activity if reproductive parts are involved. This process is also called double fertilization.
Its essence is as follows. After pollination of the plant, fertile (active) pollen falls on the stigma of the pestle and is held there, thanks to a viscous medium and special sticky components. Then, the absorbed cell begins to grow inside the column, forming a pollen tube. It is through it that two sperm with a haploid set of chromosomes get to the ovary. Once inside the ovule, one of them merges with the egg, which is fully formed and ready for this process. So there is a zygote - diploid and subsequently giving rise to a seed.
The second sperm inside the ovule fuses with the diploid cell located in the center. As a result, an endosperm is formed. The following processes complete reproductive function:
- from integrations of ovule, a seed peel is formed;
- the walls of the base of the pestle form pericarp;
- ovule forms the whole seed as a whole.
The result is the development of seeds within the fetus.
Pollination methods
There are several main options due to which pollen falls on the stigma of the pestle. So, consider the methods of pollination of angiosperms:
- Self-pollination - without the participation of extraneous individuals.
- By the wind.
- Thanks to insects, animals, birds.
- Using water.
- Artificial pollination - with the help of people.
Vegetative propagation
The propagation of flowers is also carried out vegetatively, that is, without the participation of sexual processes. These methods are very diverse. The bottom line is to use different parts of the shoot (root, leaves, stem). Some of the most common options are:
- layering;
- mustache;
- vaccination;
- rooted
- leaf and petiole.
Most of these methods are used by people in the cultivation of vegetable and fruit crops.
Seeds of angiosperms
Different plants have different seeds. The structure of this structure is similar, but the shape, composition, color can vary. In addition, plants can be single and perennial. Annuals reproduce only by seeds, which ripen, as a rule, by the end of summer. Thus, a new generation will appear only in the next growing season. Seeds of annual flowers are often used by people to get all kinds of ornamental plants. The latter include asters, eschscholtsia, marigolds, begonias, dope, calendula, left-handed, cosmea, miralibis and many others.
Flowering fruits
Flower and fruit are the most important parts of the angiosperms. It is they that allow these plants to exist in different conditions, to be widely adapted and numerous.
The fruits of plants are distinguished by great species diversity, their consideration, classification and significance is studied by botanists of the whole world, the science of them is called carpology. The most common are berries, drupes, apple, pumpkin, pomegranate, pod, bean, caryopsis, leaflet, lionfish, hesperidium and others.