Gymnastics are the most ancient seedplants of our planet. They played an important role in the development of wildlife and continue to occupy a significant position in the life of the Earth. Spruce, pine, fir, thuja, yew or larch, and little-known velvichia, saga or ginkgo, well known to us, are all representatives of the group called "Gymnosperms". The structure and reproduction of them we consider further in the article.
Origin and age
Age of gymnosperms - 350 million years.They appeared in the upper Devonian (Paleozoic) and by the beginning of the Mesozoic era had already reached their heyday. Presumably, their origin is associated with the gradual evolution of spore ferns. In comparison with them, a new species of plants already had ovules and pollen grains directly involved in the formation of a seed. There were a number of advantages possessed by the gymnastics:
- reproduction took place without water;
- seed coat and nutrient supply ensured the safety of the seedling.
For these reasons, after a short time, greenThe cover of the planet was already mostly gymnosperms, the structure and reproduction of which contributed to the successful development of new territories and ecological niches.
Features of the structure
Mostly named plants grow inthe form of trees and shrubs, often - evergreen, and rarely - deciduous. Sometimes they can reach huge sizes (sequoia, cedar). The leaves are overwhelmingly needle-shaped or have the appearance of scales. They are called pine needles and contain resin courses.
Wood makes up most of the trunk. It contains hollow dead cells with perforated walls - tracheids. Their presence is a sign specific to this group of plants. It is through them that an upward flow of water from the root to the leaves is carried out.
In addition to tracheids, gymnosperms wood containsalso pitch passages. Therefore, representatives of plants of this group are easily recognizable by the fragrant coniferous smell. Pitch impregnates wood that interferes with its decay. Due to this, among conifers there are a lot of long-livers. For example, the age of some redwoods has about 3 thousand years.
The most important evolutionary advantage enjoyed by the gymnosperm is reproduction without the participation of trickle moisture and the presence of formations that play the role of reproductive organs.
Breeding plants of gymnosperms
The lack of colors is a key feature of the gymnosperms. The reproduction of these plants occurs with the participation of cones, or strobe. These formations are easily recognizable on pine, spruce, fir, larch and other coniferous species. They can be called organs of sexual reproduction.
Usually the cones are different-sex - they can be male and female and can be located either on the same plant (monoecious) or on different (dioecious), differing in size and color.
Male cones are called microstrobiles, and women - megastrobiles. The strobila is a shortened and modified shoot, on which are located sporophyll - modified leaves. In microstroil ripen pollen. In megastrobiles - ovules.
Features of reproduction of gymnosperms
Usually the process of breeding gymnospermsconsidered on the example of Scots pine. It is a monoecious plant, i.e., male and female cones develop on a single tree. The first ones are larger, reddish in color. The second - small, greenish or gray.
Breeding scheme of gymnospermssimple enough. When pollen matures in microstrobiles, it is poured out, spread by the wind and can travel long distances. To do this, each pollen grain is equipped with special devices - pollen bags. Dusts fall on ovules, developing on megastrobilas. So is pollination.
It usually occurs at the end of spring or the beginning of summer. Pollinated female cones close, their scales are glued together with resin. Fertilization occurs in the ovules inside the closed buds.
How does the process of fertilization
Inside the ovule is a female gametophyte,or germinal bag, which previously passes through several stages of maturation. The pollen falls on the ovule pollen infiltration, it begins to germinate into the pollen tube in the direction of archegonia (from the Greek arche - "beginning", gone - "mother womb"). This formation contains an egg. In total, two of them develop in the ovule, but only one is fertilized.
К тому моменту в пыльцевом зерне уже созрели два sperm and started moving up the growing tube. When one of the sperm reaches the egg, fertilization occurs. The second sperm dies. After the merger of two germ cells, an embryo of the seed is formed - a zygote. The ovule itself is transformed into a seed. Growing, it will use the supply of nutrients.
This is how the gymnosperms reproduce. A diagram of this process is shown in the photograph.
Seed ripening and spreading
После того как произошло оплодотворение, Seed ripening begins. In Scots pine, both of these processes last for 2 years. Ripening, cones lignify and change color. Gradually, their scales are opened, and the seeds are poured out of them.
Gymnosperms do not form fruits. But in order to spread over long distances, the seeds have special devices - pterygoid membranous outgrowths, easily carried by the wind.
Species numbers and representatives
The described group has about 600-700 species. Not all of them have survived to this day, some representatives exist only in fossil form. For example:
- Cordaitic;
- Bennetite;
- seed ferns.
The remaining representatives are spread throughoutGlobe and grow in all climatic zones: from southern tropical (sago palms) to cold northern latitudes (cedar, larch, spruce, pine).
The oldest representative of gymnasiums,existing to this day - Ginkgo Biloba (bilobed). This plant is called living fossil, as it grows on the planet from the Mesozoic era, as evidenced by the numerous prints in the sediments of ancient rocks.
Evolutionary development
Первые голосеменные, возникшие в Палеозойской era, had a number of advantages that allowed them at that time to take a dominant position on the planet. These evolutionary new features are called aromorphoses and make it possible to reach a new level in the development of new territories and ecological niches. There are several such features that the gymnastics have:
- Reproduction is carried out without the participation of the aquatic environment. This made it possible to settle large areas on land.
- Fertilization occurs inside the ovule and is protected from external influences - such reproduction features of gymnosperm plants ensure greater safety of the future plant.
- The emergence of the seed allowed the future embryo to provide protective covers (seed coat) and food supply (endosperm), which, in turn, increased the number of plants in this group.
It was these traits that distinguished them from their ancestors - ferns. The next, and today the last, stage of the evolutionary development of the plant world is the emergence of angiosperms.
Meaning gymnosperms
Роль голосеменных растений трудно переоценить.It is they who fill about a third of the forests of the globe involved in air purification and the constant renewal of oxygen. In addition, the emergence and wide distribution of plants on the planet that produce a large amount of oxygen, has led to the emergence of other organisms that can use this gas during their breathing.
Softwood - the main suppliers of wood fordifferent spheres of human life. This raw material is actively used in the manufacture of furniture, construction, manufacture of vessels and in other strategically important areas of economic activity. Fir wood spruce is especially valuable in the manufacture of high-quality grades of paper.
Голосеменные нашли широкое применение в медицине.Special substances - phytoncides, released by almost all coniferous trees, are able to purify the air from pathogenic microbes. For this reason, most sanatoriums and health resorts are built on the territory of coniferous forests. Such therapy can significantly alleviate or eliminate many lung diseases.
