Generative organs of plants are a flower, a seed and a fruit. They provide plants with sexual reproduction. In this article, we will talk about each of these organs.
Flower
A very important generative organ of flowering plants is the flower. It is a modified shortened shoot, which serves as a reproductive organ not in all plants, but only in angiosperms. The generative organ of flowering plants that interests us is a formation that is located on the pedicel. The receptacle is the extended part of the peduncle. Here are all the parts of the flower, the main of which are the pistil and stamens. They are located in the center. The stamens are the male organ and the female is the pistil. The latter usually consists of an ovary, style and stigma. In the ovary there are ovules, where the egg is formed and matures. Anthers and filaments are the constituent parts of the stamen. Anthers contain pollen grains where sperm are produced.
Perianth
Angiosperms also have perianth. Forwhy is it needed? It is not a generative organ of angiosperms, but its leaves protect the inner parts of the flower. Sepals are its outer leaflets, usually green. They form a cup. The corolla is formed from the inner petals. A perianth is called double if it consists of a corolla and a calyx, and simple if it is composed of identical leaves. Double characteristic of roses, peas and cherries. A simple one is found in lily of the valley and tulip. The perianth is necessary not only to protect the parts of the flower inside, but also to attract pollinators. That is why it is so often characterized by a bright color. The perianth of wind-pollinated plants is often reduced. It can also be represented by films and scales (poplar, aspen, willow, birch, cereals).
Nectaries
Nectaries are special glands that some angiosperms have in their flowers. These glands secrete an odorous, sugary liquid called nectar. It is essential to attract pollinators.
Monoecious and dioecious plants
So, a flower belongs to the generative organs of a plant. There are two types of flowers based on the presence of pistils and stamens. Those plants that have both at the same time are called monoecious (cucumber, hazel, oak, corn). If pistils and stamens are present on different plants, they are called dioecious (sea buckthorn, willow, willow, poplar).
Inflorescences
Now consider the inflorescences. A plant may have either numeroussmall or solitary large flowers. Small, collected together, are called inflorescences. They are more visible to pollinators and are also more efficient for wind pollination. There are several types of inflorescences. Let's list them.
Types of inflorescences
- Spike is a type that is typical for plants that have sessile flowers on the main axis (without pedicels).
- There is also a complex spike. It is formed by combining several simple ones (examples are rye, wheat).
- The spadix is a type of inflorescence characterized by a thick central axis where the sessile flowers are found (cala worm is one example).
- A brush is when the flowers are on pedicels one after the other on a common axis. Examples are bird cherry, lily of the valley (pictured above).
- There is also such a type of inflorescence as a basket. It is typical, in particular, for dandelion and chamomile. In this case, a large number of sessile flowers are located on a thickened wide saucer-shaped axis.
- The head is another interesting type. It is characterized by the fact that small sessile flowers are on a spherical shortened axis (clover).
- There is also a simple umbrella (for example, primrose or cherry). In this case, on the main axis (shortened), the flowers are located on long identical pedicels.
- But in parsley or carrots, the inflorescences are represented by a whole group consisting of simple umbrellas. This type is called a composite umbrella.
- Unlike the brush, the corymb has flowers in the same plane. Hence,pedicels that extend from the central axis have different lengths (pear, yarrow).
- Panicle is a complex inflorescence with several lateral branches, which consist of corymbs, brushes (lilac, oats, etc.).
Part of the flowers in some inflorescences consists of only one corolla. In other words, they lack stamens and pistils. Such, for example, is the structure of flowers of plants of species such as chamomile or sunflower (pictured above).
Sexual reproduction of plants
Generative organs of plants - flower, fruit and seed. In order for a seed to form, it is necessary that the pollen located on the stamens moves to the stigma of the pistil. In other words, it is necessary for pollination to occur. In the case when pollen is on the stigma of the same flower, self-pollination occurs (wheat, peas, beans). But it often happens otherwise. In the case of cross-pollination, the pollen on the stamens of one plant is transferred to the stigma of the pistil of some other. How does she get there? How do plants reproduce? Let's find out.
Pollen vectors
Dry and fine pollen can be carried by the wind (birch, hazel, alder). The flowers of wind-pollinated plants are usually small, folded into inflorescences. They either have a poorly developed or completely absent perianth. Pollen can also be carried by insects. In this case, the plants are called insect pollinated. Birds and even some mammals can take part in this process. Usually flowerssuch plants are fragrant, bright, contain nectar. In most cases, pollen is sticky, it has special outgrowths - hooks.
For their own purposes, a person can also carry pollen, as a result of which it passes from the stamens to the stigma of the pistils. In this case, pollination is called cross-pollination. It is used, among other things, to increase yields or develop new varieties of plants.
Male gametophyte
Pollen grains, known to us as pollen, are the male gametophyte that forms in the stamens. These grains contain two cells - generative and vegetative. In the first, sperm are formed - male germ cells.
Female gametophyte
In the ovule, in the ovary of the pistil, a female gametophyte is formed. It is called the eight-core embryo sac. This gametophyte is actually a single cell containing eight haploid nuclei. One of them is larger than the others. It is called the egg and is located at the pollen entrance. There are also two smaller nuclei that are in the center. They are called central cores.
Fertilization process
If pollen gets on the stigma of the pistil, the vegetative cell begins to germinate into the pollen tube. At the same time, it moves the generative cell to the micropyle (pollen entrance). Through the last two sperm enter the embryo sac. As a result, fertilization occurs. A zygote is formed when one of the sperm fuses with the egg. It then develops into a seed germ. As for the second sperm, it merges with the central nuclei (as you remember, there are two of them). This is how the triploid endosperm of the seed is formed. It stores nutrients. The seed coat is formed from the integument of the ovule. This fertilization process is double. It was discovered by S. G. Navashin, a Russian botanist, in 1898. The fruit is formed either from the overgrown wall of the ovary, or from some other parts of the flower.
The generative organs of plants include, as you can see, also the seed and the fruit. Let's briefly characterize each of them.
Seed
The composition of the seed includes the seed coat, endosperm and germ. Outside, it is covered with a protective seed coat, quite dense. In the embryo there is a root, a kidney, a stalk and cotyledons, which in a plant are the first germinal leaves. If the embryo has one cotyledon, such a plant is called monocot. If there are two of them - dicotyledonous. Nutrients are usually found in the cotyledons or endosperm (special storage tissue). In the latter case, the cotyledons are practically not developed.
Fruit
This is a rather complex formation, in the creation of which, in addition to the pistil, some other parts of the flower can participate: the receptacle, the bases of the sepals and petals. The fruit, formed from several pistils, is composite (blackberry, raspberry).
It should be said that the shape of the fruit is very diverse. It contains a variety of seeds. On this basis, single-seeded and multi-seeded fruits are distinguished. This is related to the number of ovules in the ovary. Allocate alsodry and juicy fruits.
So, we have described generative organs of plants. In conclusion, we will talk about how seeds and fruits are distributed. As for pollen, its transfer was mentioned above.
Spreading seeds and fruits
The generative organs of plants that interest us (seeds and fruits), spreading, contribute to the flourishing of species and the dispersal of plants. They can be carried independently, which is typical for species such as yellow acacia, touchy, lupine, violet, geranium. The fruits of these plants crack after ripening and forcefully throw seeds over fairly long distances. This method of distribution is called autochory.
The wind can also carry fruit. This method is called anemochory. Hydrochory is noted if water is involved in the transfer process, ornitochory - birds, zoochory - animals. In this way, seeds of plants that have juicy fruits are transferred. On the latter, sticky substances or trailers (burdock, string, etc.) often develop. This promotes the spread of plants. The person also plays a significant role. Its influence on plant dispersal has been especially noticeable in recent times, when ties between continents and countries have increased.
So, we talked about how plants reproduce. As you can see, this process is quite complicated. However, it is very effective.
