Gymnosperms are seed plants. Unlike angiosperms, they do not form flowers and fruits, and their seeds lie “naked” on the inner sides of the cone scales. The cone is a modified shoot with scale-like leaves.

Conifers are characterized by special leaves called needles. They look like needles, are covered with a cuticle, and the stomata are deeply embedded in the leaf tissue. All this serves as a device to reduce evaporation. On average, each needle lives for several years.

The stem tissues of gymnosperms are better differentiated than those of ferns. There is bark and wood, but the core is poorly defined, and the conducting tissue consists of tracheids. Gymnosperms have a developed cambium and secondary wood, so their trunks reach significant sizes.

Coniferous trees have resin ducts in their trunks. These are intercellular cavities into which the cells lining them secrete resins and essential oils. These substances prevent the penetration of insects and bacteria.

In contrast to higher plant spores, higher seed plants (gymnosperms and angiosperms) moved further to land in the process of evolution. Their reproduction process does not depend on the availability of water. Thus, pollen from gymnosperms is carried by the wind, and fertilization occurs through a pollen tube.

Pine

Pine is widespread in the Northern Hemisphere, especially in temperate climates. This tree is undemanding to soil, but demanding to light (it is light-loving). Pine can be found not only in coniferous forests, but also in swamps, rocks, and sands. Moreover, depending on the growing conditions, pine looks different. This is how the main root of a pine tree develops strongly in the forest and goes deep. In open areas, lateral roots develop, occupying a large area near the surface. Pines growing in the forest are taller than those growing in open areas, reaching a height of about 40 meters. However, in the forest, the lower branches of pine trees die off due to lack of light. Pine growing in open areas has a more spreading shape, its branches begin at the bottom of the trunk.

The lifespan of pine is about 300 years.

Pine propagation

Male and female cones form on pine shoots in spring.

Male cones are collected in groups resembling inflorescences, are yellowish-green in color and grow at the base of the shoots. In a group, the male cones are located closely next to each other. On the underside of each scale 2 pollen sacs develop. Pollen ripens in them. Gymnosperm pollen is haploid, that is, it has a single set of chromosomes. A pine pollen grain has two air sacs. This is a device for transporting pollen by wind.

Female pine cones are larger, reddish in color, and grow individually rather than in groups. Female cones grow on the tips of the shoots. On each scale of the cone, 2 ovules develop. Ovules they call it differently ovules.

Pollination occurs in late spring or early summer. Pollen falls from the male cones and is carried by the wind. In this case, some of the pollen grains fall on the scales of female cones. After this, the scales are closed and glued together with resin.

After pollination, the female cone grows and becomes woody. In this case, fertilization does not occur. Only after a year does the pollen germinate and give rise to the male gametophyte. One of its cells is called vegetative, it develops into a pollen tube. The other cell is called generative, two sperm are formed from it. Pollen is called microspore .

The ovule is macrospore, which develops into a female gametophyte consisting of an egg and endosperm.

Along the pollen tube, one of the sperm fertilizes the egg, resulting in the formation of a zygote. Subsequently, an embryo develops from it, having a root, a stalk, several cotyledons and a bud. The seed is formed from the ovule.

Towards the end of the seed ripening, the pine cones become dark brown. The seeds ripen only by the autumn of next year. In winter, the scales of the cones separate and the seeds fall out of them.

Pine seeds have wing-shaped processes. Thanks to this, they are easily carried by the wind over long distances.

Spruce

Unlike pine, spruce is a shade-tolerant plant. Its crown grows from the very bottom of the trunk and has a pyramidal shape. Therefore, spruce forests are dark, and almost no grass grows in them due to the lack of light near the surface of the earth.

Spruce grows on fertile soils, in places with sufficient moisture.

The root system of spruce is located closer to the soil surface and is less developed than that of pine. Therefore, spruce trees do not tolerate strong winds, which can tear entire spruce plantings out of the soil.

If in pines each needle lives for several years, then in spruce they live up to 9 years. Spruce needles are located singly.

The cones were larger than those of pine. Reach 15 cm in length. In addition, one year passes from the beginning of the appearance of the cone to its ripening.

Spruce trees live up to 500 years.

The meaning of conifers

Where there are many coniferous and mixed forests, their role in the formation of oxygen and organic matter is significant.

By delaying snow melting, coniferous forests enrich the soil with moisture.

Pine produces special volatile substances that have antibacterial properties - phytoncides.

Conifers are also of great importance in human life. Since ancient times, people have used their wood as a building material. Ships were made from pine wood. Sequoia wood (mahogany) is used as a finishing material. Larch wood is resistant to rotting. Paper is made from spruce wood.

Conifers are used in the chemical industry. This is how turpentine, plastics, rosin, varnishes, and alcohols are obtained from them.

The seeds of the Siberian pine pine look like nuts. They are eaten and oil is made from them.

Juniper cones look like berries. They are used as medicine.

Among the conifers there are ornamental plants.

General characteristics. The first gymnosperms appeared at the end of the Devonian period about 350 million years ago; they probably descended from ancient pteridophytes that became extinct at the beginning of the Carboniferous period. In the Mesozoic era - the era of mountain building, the rise of continents And drying climate - gymnosperms reached their peak, but already from the middle of the Cretaceous period they lost their dominant position to angiosperms. Gymnosperms include the following classes:

Ginkgoids (Ginkgophyta);

Oppressive (Gnetophyta);

Cycads (Cycadophyta);

*Coniferous or Pine

The department of modern gymnosperms includes more than 700 species. Despite the relatively small number of species, gymnosperms have conquered almost the entire globe. In the temperate latitudes of the Northern Hemisphere, they form coniferous forests called taiga over vast areas.

Modern gymnosperms are represented mainly by trees, much less often by shrubs and very rarely by lianas; There are no herbaceous plants among them. The leaves of gymnosperms differ significantly from other groups of plants not only in shape and size, but also in morphology and anatomy. In most species they are needle-shaped (needles) or scale-like; in some representatives they are large (for example, in the amazing Velvichia their length reaches more than 2-3 m), pinnately dissected, bilobed, etc. The leaves are arranged singly, two or several in bunches.

The vast majority of gymnosperms are evergreen, monoecious or dioecious plants with well-developed stems and root systems formed by the main and lateral roots. They spread by seeds, which are formed from ovules. The ovules are glabrous (hence the name of the department), located on megasporophylls or on seed scales collected in female cones.

In the development cycle of gymnosperms, there is a successive change of two generations - the sporophyte and the gametophyte with the dominance of the sporophyte. Gametophytes are greatly reduced, and male gametophytes of holo- and angiosperms do not have antheridia, which sharply differs from all heterosporous seedless plants.

Gymnosperms include six classes, two of which have completely disappeared, and the rest are represented by living plants. The best preserved and most numerous group of gymnosperms is the class Conifers, numbering at least 560 species, forming forests over vast areas of Northern Eurasia and North America. The largest number of species of pine, spruce, and larch are found along the coasts of the Pacific Ocean.

Class Conifers. All conifers are evergreen, less often deciduous (for example, larch) trees or shrubs with needle-like or scale-like (for example, cypress) leaves. The needle-shaped leaves (needles) are dense, leathery and hard, covered with a thick layer of cuticle. The stomata are immersed in depressions filled with wax. All these structural features of the leaves ensure that conifers are well adapted to growing in both arid and cold habitats.

Conifers have erect trunks covered with scaly bark. In a cross section of the stem, developed wood and less developed bark and pith are clearly visible. The xylem of conifers is 90-95% formed by tracheids. Conifer cones are dioecious; plants are more often monoecious, less often dioecious.

The most widespread representatives of conifers in Belarus and Russia are Scots pine and Norway spruce, or Norway spruce. Their structure, reproduction, and alternation of generations in the development cycle reflect the characteristic features of all conifers.

Scots pine-monoecious plant (Fig. 9.3). In May, bunches of greenish-yellow male cones, 4-6 mm long and 3-4 mm in diameter, form at the base of young pine shoots. On the axis of such a cone there are multilayer scaly leaves, or microsporophylls. On the lower surface of the microsporophylls there are two microsporangia - pollenbag , in which pollen is formed. Each pollen grain is equipped with two air sacs, which facilitates the transfer of pollen by wind. The pollen grain contains two cells, one of which subsequently, when it hits the ovule, forms a pollen tube, the other, after division, forms two sperm.

Rice. 9.3. Development cycle of Scots pine: a - branch with cones; b- cross-section of a woman's cone; c - seed scales with ovules; G - ovule in section; d - cross-section of a male cone; e - pollen; and - seed scales with seeds; 1 - male cone; 2 - young female bump; 3- bump with seeds; 4 - lump after spilling seeds; 5 - pollen passage; 6 - cover; 7 - pollen tube with sperm; 8 - archegonium with egg; 9 - endosperm.

On other shoots of the same plant, female cones of a reddish color are formed. On their main axis there are small transparent covering scales, in the axils of which there are large, thick, subsequently lignified scales. On the upper side of these scales there are two ovules, each of which develops female gametophyte - endosperm with two archegonia with a large egg in each of them. At the apex of the ovule, protected from the outside by the integument, there is an opening - the pollen passage, or micropyle.

In late spring or early summer, ripe pollen is carried by the wind and lands on the ovule. Through the micropyle, pollen is drawn into the ovule, where it grows into a pollen tube, which penetrates the archegonia. The two sperm cells formed by this time travel through the pollen tube to the archegonia. Then one of the sperm fuses with the egg, and the other dies. A seed embryo is formed from a fertilized egg (zygote), and the ovule turns into a seed. Pine seeds ripen in the second year, fall out of the cones and, picked up by animals or the wind, are transported over considerable distances.

In terms of their importance in the biosphere and role in human economic activity, conifers occupy second place after angiosperms, far surpassing all other groups of higher plants.

They help solve enormous water conservation and landscape problems, serve as an important source of wood, raw materials for the production of rosin, turpentine, alcohol, balms, essential oils for the perfume industry, medicinal and other valuable substances. Some conifers are cultivated as ornamental trees (fir, thuja, cypress, cedar, etc.). The seeds of a number of pine trees (Siberian, Korean, Italian) are used as food and oil is also obtained from them.

Representatives of other classes of gymnosperms (cycads, cycads, ginkgos) are much less common and less known than conifers. However, almost all types of cycads are decorative and are widely popular among gardeners in many countries. Evergreen leafless low shrubs of ephedra (Gnetaceae class) serve as a source of raw materials for the production of the alkaloid ephedrine, which is used as a central nervous system stimulant, as well as in the treatment of allergic diseases.

General characteristics. Features of the life cycle. Reproductive organs. Strobili (cones)

Class Seed ferns – Pteridospermae

Class Bennettitaceae – Bennettitopsida

Class Ginkgoaceae – Ginkgoopsida

Class Conifers – Pinopsida

Subclass Cordaitidae – Cordaitidae

Subclass Conifers – Pinidae

Family Araucariaceae - Araucariales

Cypress family – Cupressales

Family Taxodiaceae – Taxodiaceae

Order Yew – Taxales

Family Pine – Pinales

Division Gymnosperms – Pinophyta, or Gymnospermae

Gymnosperms, like Angiosperms, are the main producers of terrestrial ecosystems on the planet, differing from spore-bearing plants in that their main means of dispersal is not spores, but seeds. A seed is a stage of the life of a sporophyte, a special formation in which the future adult sporophyte - the embryo, as well as a supply of nutrients - the endosperm, is located in a compact and protected from unfavorable conditions state.

“Internal fertilization, the development of the embryo inside the ovule and the emergence of a new, extremely effective unit of dispersal - the seed - are the main biological advantages of seed plants, which gave them the opportunity to more fully adapt to terrestrial conditions and achieve higher development than ferns and other seedless higher plants. If during propagation by spores a huge number of them are formed each time, usually millions, then when propagated by seeds their number is many times smaller. A seed is a more reliable unit of dispersal than a spore. The seed already contains an embryo - a tiny sporophyte with a root, bud and embryonic leaves (cotyledons), a supply of nutrients and the necessary enzymatic apparatus. A seed is truly a small masterpiece of evolution” (Takhtadzhyan A.L. Plant life. T.4. 1978. P.258).

Wood consists only of tracheids (with the exception of representatives of the Gnetaceae class). The leaves are narrow (needle-shaped) or scale-like, although there are genera with broad leaves.

The heyday of Gymnosperms was the Mesozoic; they have reached our time in limited diversity. At the same time, modern Gymnosperms are clearly divided into 2 groups: the 1st includes the class Cycads - Cycadopsida and Ginkgos - Ginkgoopsida. These are "living fossils". 2nd group – Conifers, which are the main gymnosperms.

Standing apart are the Gnetopsida, which are classified as Gymnosperms with a considerable degree of convention.

Life cycle features

In Gymnosperms there is an increasing tendency to care for the gametophyte. Thus, not only does the female gametophyte not leave the microspore shell, but the macrospore also remains in the macrosporangium, thus the female gametophyte does not come into contact with the external environment and maintains a constant connection with the sporophyte; The male gametophyte is even more reduced; as in heterosporous plants, it develops in a microspore shell; the multicellular antheridia are replaced by a new formation of auxiliary vegetative prothallials (from the Greek. prothallium- “vegetative part”) of cells that serve gametogenic antheridial cells, producing a very small (usually 2) number of male gametes.

In primitive groups of 2 antheridial cells, a haustorium (haustorial cell) develops from one cell, then it divides into 2 more cells, one of which either forms 2 sperm (spermatogenic) or 2 sperm (spermagenic). The second antheridium cell remains sterile and is then destroyed. The process of fertilization in seed plants gets rid of the connection with the aquatic environment.

The male gametophyte, called pollen, is carried entirely by the wind to the female gametophyte, where it germinates using the nutrients from the female gametophyte (Figure 1).

Rice. 1. Development of the male gametophyte of Scots pine (Pinus sylvestris )

A – division of the archesporial cell; B – tetrad of microspores; B – microspore; G-E – formation of male gametophyte (pollen); G – pollen germination: 1-2 – prothallial cells, 3 – antheridial cell, 4 – vegetative cell, 5 – stalk cell, 6 – spermagen cell.

The ovule consists of a macrosporangium - nucellus, protected by an additional cover - integument. At the apex of the ovule, the integument is not closed; its edges form an opening—the micropyle. Inside the nucellus, the female gametophyte develops, which is a colorless multicellular body, the cells of which accumulate a significant amount of reserve substances, mainly oils. At the end of the gametophyte facing the micropyle, 2 archegonia immersed in its tissue are formed, in the abdomen of each of which there is a large egg. Other more primitive conifers may have dozens of archegonia (Araucariaceae - 25, cypress - up to 200).

After fertilization, a seed is formed from the ovule. The integument turns into the seed coat, the nucellus is consumed by the developing embryo, leaving a thin film. The tissues of the prothallus or endosperm grow strongly and nutrients are deposited in them (Fig. 2).

Rice. 2. Development of the sexual generation of pine.

A – pollen grain; B – formation of the male gametophyte; 1 – prothallial cell; 2 – antheridial cell; 3 – air bags; B – pollen tube; 4 – generative cells (sperm); G – longitudinal section of the ovule; D – upper part of the ovule; 5 – integument; 6 – micropyle; 7 – nucellus; 8 – pollen tube; 9 – endosperm; 10 – neck of the archegonium; 11 – egg; 12 – female gametophyte.

From the fertilized egg, an embryo is formed, consisting of a root, a stalk and a bud with 2-18 cotyledons.

In living fossils, seeds fall before full maturity and even before fertilization (the so-called “oviparous” plants); in conifers, the seed leaves the mother’s body in a state of full readiness for the development of a daughter sporophytic plant (“viviparous”). Seeds of “oviparous” plants germinate without a dormant period.

Strobili (cones)

In Gymnosperms, micro- and macrosporophylls can develop on one (monoecious) or on different individuals (dioecious). Despite the diversity of their structure, a general pattern is visible: the older the taxon, the larger the size of the macro- and especially microsporophylls, which can even be pinnate, resembling the leaves of ferns (as in the extinct Bennettites).

In more developed Gymnosperms, sporophylls become scale-like and unite into strobili (cones), convenient for ripening, protecting and dispersing seeds. Adaptations arise for the dispersal of seeds due to the integument of the seed itself or parts of the seed cones. In all living gymnosperms, the strobili are unisexual, male strobili are called microstrobilae, female strobili are called macrostrobilae (megastrobili). The taxonomy of Gymnosperms is quite complex.

Questions for independent work

1. List the most important orders and families of the Cycadaceae class.

2. Give a general description, the structure of vegetative and reproductive structures. Write down the life cycle diagram in your notebook.

3. Give a description of the Gnetovye class. What is the scope of the taxon?

4. Tell us about the structural features of the Gnetov sporophytes.

5. From what ancestors do the Gnetovs originate? What is the phylogenetic significance of the Gnetovs?

Fill in the missing word.

1. Complete the sentences by inserting the necessary words.

B. The seeds lie... on the scales.

D. The class of conifers includes: ..., ..., ...

G. The stem of conifers consists of: ..., ..., ...

3. Coniferous leaves are needle-shaped and covered...

Find a match.

2. Write down the letters indicating the signs characteristic of:

I. Male cones

II. Women's bumps

B. Pollen sacs

B. Ovum

G. Endosperm

D. Microspore

E. Megaspore

G. Pollen grain

3. Sperm

I. Ovule

3. Complete the “Pine Tree Reproduction” diagram.

Choose the correct answer.

4. Seed as opposed to spore:

A. Participates in reproduction

B. Has an embryo and endosperm

B. Formed in boxes

D. Most adapted to survive adverse conditions

5. Leaves grow throughout the life of the plant in:

A. Larches

V. Velvichia

G. Cycad

6. Tracheids are:

A. Plant name

B. Sex cells

B. Wood cells

7. Conifers tolerate severe frosts thanks to:

A. Thick bark

B. The needles are covered with a thick cuticle

B. The stomata are buried deep in the leaf tissue, which reduces water evaporation and prevents hypothermia

D. Needles are shed for the winter

Choose the correct statement.

2. A supply of nutrients is formed in the seed, which ensures the life of the embryo.

4. The stem of coniferous trees is covered with wood.

6. Conifer leaves are covered with cuticle.

7. Coniferous bisexual plants.

8. In pine trees, 2–4 months pass between pollination and fertilization.

9. On the territory of Russia, about 40% of forests are represented by various types of gymnosperms.

10. Externally, cycads resemble pine trees.

11. Plants belonging to the Cedar genus grow in South and North America.

12. Sperm has a double (diploid) set of chromosomes.

13. The egg has a single (haploid) set of chromosomes.

14. The zygote has a double (haploid) set of chromosomes.

15. Wood cells have a single (haploid) set of chromosomes.

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Gymnosperms are plants that produce seeds but do not form flowers or fruits. The seeds lie open and are only sometimes covered with scales. Gymnosperms evolved from the primordial ones. Currently, this group includes only about 700 species of trees and shrubs. The plant department includes the following divisions: cycads, ginkgos, conifers, ephedras. Conifers are the most widespread. Almost all of them are trees. Conifers have a well-defined trunk, the leaves of most conifers are hard, needle-like (needles) and do not fall off; are replaced almost throughout life. The structure of gymnosperms has characteristic features. Among gymnosperms there are a large number of woody forms, sometimes having a large, well-defined trunk. Conifers are characterized by the longest life expectancy. In a transverse section of the stem, a thin bark, well-developed wood (conductive tissue) and a poorly defined core consisting of loose parenchyma (ground) tissue are distinguished. In old trunks the core is barely noticeable. The wood of gymnosperms is simpler than that of flowering plants; it consists mainly of tracheids - dead spindle-shaped cells with thick shells that perform a conducting and supporting function.

Parenchyma there is very little or no wood in the wood. Many species have very little or no bark and wood. Many species have resin canals in the bark and wood filled with resin, essential oils and other substances. The evaporation of these substances creates the characteristic aroma of a coniferous forest.

The leaves of most conifers are hard, needle-like (needles) and do not fall off at unfavorable times of the year. They are covered with a thick cuticle - a layer of a special substance secreted.

The stomata are immersed in tissue, which reduces water evaporation: needles are replaced gradually throughout the life of the plant.

Reproduction of conifers using the example of pine

This is a bisexual, wind-pollinated plant. On young stems, two types of cones are formed - shortened: male and female. Male cones are located at the base of young shoots and have an axis to which scales are attached. On the underside of the scales there are two pollen sacs, in which microspores (male spores) with a single haploid set of chromosomes are formed. From microspores, male gametophytes are formed - pollen grains carrying germ cells - sperm.

Small reddish female cones sit on the tops of young shoots. The scales of female cones grow together in pairs, and the scales develop between them. A megaspore (female spore) is formed there. As a result of its repeated division, a female gametophyte is formed - an egg and an endosperm, which subsequently nourishes the embryo. Pollen carried by the wind lands on the scales of female cones. The pollen grain germinates, the sperm reaches the egg through the pollen tube and fuses with it - fertilization occurs. When they unite, the sperm and egg form a cell with a double (diploid) set of chromosomes - a zygote. This is the first cell of the sporophyte. From the seven germ a seed develops with a supply of nutrients, which is covered with protective shells. In the second year after the formation of a female cone and the transfer of microspores to it, the seeds spill out and are carried by the wind.

- the basis of vegetation cover in a number of natural zones. 90% of forests are represented by different types of gymnosperms. Birds feed on the seeds, and the wood is used on the farm.

The so-called ship pines, which have a long straight trunk, were used in shipbuilding in earlier times. The entire sailing fleet was built mainly from pine. Many conifers are still an excellent building material. In addition, paper, cardboard, turpentine and many other products valuable to humans are obtained from pine. The pith of cycads is eaten.

Plants play a very important role in nature because they are capable of photosynthesis. This is the process by which a plant obtains nutrients from carbon dioxide, water and solar energy and releases oxygen into the atmosphere. Therefore, it is thanks to plants that animals and you and I can exist on Earth.

Plant classification

Everything is divided into ten departments:

• Brown algae.
• Green algae.
• Blue-green algae.
• Red algae.
• Bryophytes.
• Fern-like.
• Horsetails.
• Moss-shaped.
• Angiosperms.
• Gymnosperms.

Among these plants, depending on the complexity of their structure, two groups can be distinguished:

• inferior;
• higher.

All departments of algae belong to the lower ones, since they lack tissue differentiation. The body has no organs. It's called a thallus.

Higher plants, depending on the method of reproduction, can be divided into:

• spore;
• seed.

The spore-forming species include fern-like, lycophyte, mossy, and horsetail-like.

Classification of gymnosperms

The next taxon that stands out in all departments of the kingdom “Plants” is a class. Gymnosperms are divided into four classes:

1. Gnetovye.
2. Ginkgo.
3. Cycads (Cicadas).
4. Conifers.

We will talk about the representatives and features of each class later. And now we will consider the common features of all gymnosperms, their physiology and biology.

Gymnosperms: plant structure

This department belongs to higher plants. This means that their body consists of organs that are built from different types of tissue.

Organs of gymnosperms

Depending on the location of the organs, they can be divided into underground and above-ground. Considering their functions and structure, we can distinguish vegetative and generative organs.

Vegetative organs: structure and functions

This group of organs includes the underground root system and above-ground shoots.

The root system consists of many roots, among which one main and many lateral roots can be distinguished. In addition, the plant may have additional roots.

The root has the following functions:

• Fixing the plant in the soil.
• Absorption of water with micro- and macroelements dissolved in it.
• Transportation of water and minerals dissolved in it to terrestrial organs.
• Sometimes - storing nutrients.

The escape is also an organ system. It consists of a stem, leaves and buds.

Functions of the escape organs:

• Stem: supporting and transport functions, providing communication between roots and leaves.
• Leaves: photosynthesis, respiration, gas exchange, temperature regulation.
• Buds: new shoots are formed from them.

Generative organs of gymnosperms

Generative organs are those that ensure the reproduction of the organism. In angiosperms it is a flower. But the plants of the “Gymnosperm plants” department, for the most part, have generative organs such as cones. The most striking visual examples are spruce and pine cones.

Cone structure

It is a modified shoot covered with scales. There are male and female cones, in which male and female reproductive cells (gametes) are formed, respectively.

Male and female pine cones as an example can be seen in the photo below.

There are representatives of gymnosperms in which both male and female plants are located on the same plant. They are called monoecious. There are also dioecious gymnosperms. Their male and female cones are in different species. However, the plants of the “Gymnosperms” department are mostly monoecious.

On the scales of female cones there are two ovules, on which female gametes are formed - eggs.

The scales of male cones contain pollen sacs. They form pollen, which contains sperm - male reproductive cells.

How a pine tree grows from a cone

Pollination of female cones occurs with the help of wind.

After fertilization, seeds develop from the ovules, which are located on the scales of female cones. From these, new representatives of gymnosperms are then formed.

What tissues do organs consist of?

There are the following types of plant tissues:

• Integumentary. These fabrics perform a protective function. They are divided into epidermis, cork and crust. The epidermis covers all parts of plants. It has stomata for gas exchange. It can also be coated with an additional protective layer of wax. The plug forms on the trunk, roots, branches and bud scales. The crust is a covering tissue consisting of dead cells with woody membranes. The bark of gymnosperms consists of it.
• Mechanical. This tissue provides strength to the stem. It is divided into collenchyma and sclerenchyma. The first is represented by living cells with thickened membranes. Sclerenchyma consists of dead cells with woody membranes. Mechanical fibers are part of the composition contained in the stems of gymnosperms.
• Main fabric. It is the basis of all organs. The most important type of basic tissue is assimilation. It forms the basis of the leaves. The cells of this tissue contain a large number of chloroplasts. This is where photosynthesis occurs. Also in the organs of gymnosperms there is such a type of basic tissue as storage. It collects nutrients, resins, etc.
• Conductive fabric. Divided into xylem and phloem. Xylem is also called wood, and phloem is also called phloem. They are found in the trunk and branches of the plant. The xylem of gymnosperms consists of vessels. It ensures the transportation of water with substances dissolved in it from the root to the leaves. The phloem of gymnosperm species is represented by sieve tubes. Bast is designed to transport substances from leaves to roots.
• Educational fabrics. From them all other tissues of gymnosperms are formed, from which all organs are then built. They are divided into apical, lateral and intercalary. The apical ones are located at the top of the shoot, as well as at the tip of the root. The lateral educational tissues are also called cambium. It is located in the tree trunk between the wood and the bast. Intercalated educational tissues are located at the base of the internodes. There are also wound formation tissues that arise at the site of injury.

Gymnosperms: examples

When we already know how the plants of this department are arranged, let's look at their diversity. Next, representatives of the various classes that are included in the “Gymnosperms” department will be described.

Class "Gnetovye"

1. Family "Velvichiaceae".
2. Family "Gnetovye".
3. Family "Conifers".

Let's look at the most prominent representatives of these three groups of plants.

So, Velvichia is amazing.

This is the only representative of the Velvichiaceae family. This representative of gymnosperms grows in the Namib Desert, as well as in other deserts of South-West Africa. The plant has a short but thick trunk. Its height is up to 0.5 m, and its diameter reaches 1.2 m. Since this species lives in the desert, it has a long main root that goes 3 m deep. The leaves that grow from the trunk of Welwitschia are a real miracle. Unlike the leaves of all other plants on Earth, they never fall off. They constantly grow at the base, but periodically die off at the ends. Constantly renewing itself in this way, these leaves live as long as Welwitschia itself (specimens are known that have lived for more than 2 thousand years).

The Gnetaceae family contains approximately 40 species. These are mainly shrubs, vines, and less often trees. They grow in the tropical forests of Asia, Oceania, and Central Africa. In their appearance, the Gnetaceae are more reminiscent of the representatives of this family: melinzho, broad-leaved gnetum, ribbed gnetum, etc.

The conifer family includes 67 plant species. In terms of life form, these are shrubs and subshrubs. They grow in Asia, the Mediterranean and South America. Representatives of this family have scaly leaves. Examples of conifers include American ephedra, horsetail ephedra, coniferous ephedra, green ephedra, etc.

Class "Ginkgo"

This group includes one family. The only representative of this family is Ginkgo biloba. This is a tall tree (up to 30 meters) with large fan-shaped leaves. This is what appeared on Earth 125 million years ago! Ginkgo extracts are often used in medicine to treat vascular diseases, including atherosclerosis.

Class "Cycads"

They grow in Asia, Indonesia, Australia, Oceania, and Madagascar.

These plants look like palm trees. Their height ranges from 2 to 15 meters. The trunk is generally thick and short in comparison to thickness. Thus, in a drooping cycad, its diameter reaches 100 cm, while its height is 300 cm.

Class "Conifers"

This is perhaps the most famous class of the gymnosperm department. It is also the most numerous.

This class consists of one order - "Pine". Previously, there were three more orders on Earth, but their representatives became extinct.

The order mentioned above consists of seven families:

1. Capitulaceae.
2. Yew.
3. Sciadopitisaceae.
4. Podocarpaceae.
5. Araucariaceae.
6. Pine.
7. Cypress.

The capitate family includes 20 representatives. These are evergreen shrubs and trees. The needles are arranged in a spiral. Capitate yews differ from yews in that their cones take much longer to ripen, and they also have larger seeds.

The yew family includes about 30 species of shrubs and trees. All plants in this family are dioecious. Examples of representatives of this family include the Pacific yew, Florida, Canadian, European yew, etc.

The Sciadopitis family includes evergreen trees that are often used as ornamental trees.

Examples of representatives of the podocarp family include dacridium, phyllocladus, podocarp, etc. They grow in humid areas: New Zealand and New Caledonia.

The Araucariaceae family includes about 40 species. Representatives of this family existed on Earth already during the Jurassic and Cretaceous periods. Examples include southern dammara, Brazilian Vollemia nobilis, etc.

The pine family includes such well-known trees as spruce, pine, cedar, larch, hemlock, fir, etc. All plants included in this family grow in the Northern Hemisphere in a temperate climate. Gymnosperms of this family are often used by humans in medicine and other industries due to their resins and essential oils.