On the female seed scales. Pine development cycle
The ancestors of gymnosperms were seed ferns, which arose from tree ferns. All their representatives are woody plants with a complex development cycle, in which asexual generation dominates in the form of a tree itself, and the sexual generation is greatly simplified and develops on an asexual generation. After fertilization, an embryo is formed, immersed in a seed that lies openly on the surface of the seed scales, hence the name - gymnosperms (we will consider the development cycle in detail below using the example of conifers).
The most ancient class, seed ferns, became extinct. According to paleontological data, they had straight unbranched stems with a rosette large leaves on the top. On special leaves, sporangia developed, which then turned into seeds, with a small embryo of future plants.
The Ginkgo class is also very ancient, from which one species of ginkgo biloba has survived - Ginkgo b i 1 o b a, a tree with fan-shaped bilobate leaves. It is rare in the wild, cultivated in China, Japan and in botanical gardens.
Of the greatest importance in nature and human practice are representatives of the coniferous class - Coniferae, which are widespread throughout the globe. They dominate in the taiga zone. In the Soviet Union, 75% of forests are composed of conifers... All conifers are characterized by monopodial (indefinite) branching and secondary thickening of the trunk, the presence of only tracheids in the wood of the conductive elements, and needle-like or scale-like leaves. All of them are evergreens, with the exception of several genera, including the genus larch, the species of which shed their needles for the winter.
Let us consider the development cycle of conifers using the example of Scots pine - Pinus sylvestris. Free-growing pine blooms from 15 years old, flowering in the forest begins after 25-30 years. Male and female inflorescences - cones are formed in mid or late May on the same tree (pine is a monoecious plant). Small, about 5 mm long, yellow male cones are clustered - 15-30 pcs. at the base of the young shoot (Fig. 66). Each cone consists of a short axis with elongated scales densely located on it: on the underside of them there are two oval anthers, in which pollen is formed. Each scale with two anthers is a pine stamen.
Inside the anthers there is an archesporic tissue, the cells of which, as in the sporangia of the fern, divide reductively, then karyokinetically, as a result of which four haploid cells are formed - pine pollen. Each speck of dust consists of one cell with two shells, and the upper shell in two places recedes from the lower one, forming air sacs, which reduces specific gravity pollen and facilitates its transport by wind over long distances. When the pollen ripens, the anthers burst, the pollen spills out and is carried by the wind. Further development of pollen occurs even in the anthers. The pollen nucleus is divided into two (Fig. 67). One remains the nucleus of the pollen cell and is now called the nucleus of the vegetative cell. The second nucleus, dividing, forms the nuclei of four small cells. One of them, usually the larger one, becomes the anteridial cell, the other three dissolve. The anteridial cell divides and forms two generative cells - sperm cells (male gametes). During this time, pollen from the anthers is carried by the wind to the surface of the ovule and germinates. Its outer shell bursts, and the inner one stretches into the pollen tube, into which the cytoplasm with the nucleus of the vegetative cell and two sperm are poured (they cannot move independently).
Very small, 3-4 mm long, female pine cones are formed in 2-3 pieces. on top of young shoots (see Fig. 66, 6).
They consist of a short axis, on which scales are densely located, differing in size and shape. Some - very small ones - are called covering scales, in their sinuses there are larger fleshy seed scales. On the inner side of the seed scales, at their very base, two oval bodies develop - two ovules (ovules).
The ovules have a complex structure. From above, they are covered with a special tissue - a cover, the edges of which at the top of the ovule do not close, forming a narrow opening - the pollen duct (Fig. 67, d). Under the cover is the multicellular body of the ovule - nucellus. One of the nucellus cells grows rapidly and divides twice, first by reduction, then karyokinetically, forming four haploid cells lying one above the other. The three upper cells dissolve, the fourth, expanding, fills inner part ovules, only a thin layer under the cover remains of nucellus. This large haploid cell is called the embryo sac. Its nucleus divides many times, cells appear and the cavity of the embryo sac is filled with endosperm tissue. Then, in the upper part of the endosperm, two larger cells are formed - eggs (female gametes), and above each of them, four small cells form, as it were, a channel leading to the egg. This completes the development of the pine ovule before fertilization.
Scales female cones by this time, they move apart, bend back, and the pollen is carried by the wind onto the surface of the ovule into the pollen duct. Pine has pollen there for a whole year and only germinates next spring. In other conifers, it germinates immediately.
Pine pollen germinated a year later forms a pollen tube that grows to the ovum. The nucleus of the vegetative cell at this time dissolves, the contents of the pollen tube are poured into the egg, and the first sperm merges with the nucleus of the egg, and the second sperm dissolves. The fertilized egg becomes a diploid zygote cell, becomes covered with a membrane. The second egg dissolves.
The zygote divides, and an embryo is formed from it with root rudiments (see Fig. 66, 14) of the stem and with four to eight cotyledons, after which it stops growing and passes into. a state of rest. By this time, a supply of nutrients is deposited in the endosperm. The cover of the ovule becomes the seed coat, and the entire ovule becomes the seed. In most conifers, seeds ripen within a year. In a pine, it takes 18 months from the beginning of the flowering of a female cone to the ripening of seeds in it. During this time, the female cones increase in size, the seed scales become stiff, and a filmy winglet is formed on the seeds. In ripe cones, the scales bend back, the seeds fall out and are carried by the wind. A sprout grows from an embryo, a germinating seed, which then develops into a tree, and the cycle of pine development begins again.
Reproduction of seed plants was studied much earlier than higher spore plants, and their reproductive organs were named: stamen, anther, pollen, ovule, embryonic sac. Later, the developmental cycle of higher spore plants was studied and outgrowths, antheridia, archegonia were found.
There are many similarities in the structure of the male pine cone and the spikelet of the lyre: there is a main axis, scales and sporangia on them, which correspond to anthers in pine. In the anthers, as in the sporangia, archesporia develops, the cells of which in both the pine and the lymphoids divide twice - first by reduction, then karyokinetically, forming four haploid cells, which are called microspores in heterosporous lymphoids, and pollen in pine. The formation of haploid cells, microspores or pollen in both the lyre and pine ends the development of the asexual generation and the development of the sexual generation, the gametophyte, begins. In heterosporous lymphoids, a small male outgrowth develops inside the microspore, and in it - an antheridium with spermatozoa.
In pine, in the pollen (respectively, in the microspore), a vegetative cell and a thread, a primitive male outgrowth, develop, and an anteridial cell (corresponding to anteridium) is formed in it. As a result of division of the anteridial cell, two sperm (gametes) are formed, which differ from spermatozoa only by immobility. This is the end of the development of the gametophyte - the male sexual generation of the lyre and pine.
The female pine cone is also very similar in structure to the spikelet of a lymphoid: there is an axis, scales and sporangia on them, to which the ovules correspond to the pine. In the ovules, after the reduction and then karyokinetic division of the nuclei, haploid cells are formed, in the macrospores, only there are several of them, in the pine one cell of four haploid cells is preserved - the embryo sac. In pine, as in heterosporous lymphoids, in the macrospore (embryonic sac), the tissue of a female sprout is formed - the endosperm, and in it there are two oocytes with remnants of archegonia in the form of eight small cells. This ends the development of the female sexual generation - the gametophyte in both the lyre and the pine.
With the fusion of gametes and the formation of a zygote (diploid cell), both in a lyre and a pine, the development of asexual generation, an embryo, then an adult plant with roots, stems and leaves begins. All these organs in pine have diploid cells, and only with the reduction of cell division in the anthers and ovules during the formation of pollen (microspores) and embryo sac (macrospores), the development of the sexual generation of pine begins, which has a very primitive structure. The male sexual generation of pine consists of pollen (microspores), a vegetative cell and a thread in it (male sprout), an anteridial cell (antheridium) and two sperm (corresponding to spermatozoa). The female reproductive generation of pine develops on the mother plant in the ovules (macrosporangia) and consists of an embryo sac (macrospores), endosperm (female outgrowth) and two eggs with eight small cells (remnants of archegonium). The fusion of gametes leads to the formation of a diploid zygote and the development of a new, asexual generation.
Thus, in conifers, two generations alternate - sexual and asexual. Asexual generation dominates among them, and the female sex generation develops completely on the asexual generation.
The differences in the developmental cycles of gymnosperms and ferns are as follows: in gymnosperms, the female sexual generation develops on asexual, in ferns, separately on the soil; in gymnosperms, the male sexual generation is greatly simplified and forms immobile spermatozoa, in ferns - motile spermatozoa; in gymnosperms, it is separated from the mother plant and serves for seed reproduction (overgrown sporangium with an outgrowth and embryo), in ferns - a spore; in gymnosperms, the dormant stage falls on seeds, in ferns, on a spore; in gymnosperms by appearance macro- and microspores, sporangia and even male and female cones differ, in most of the fern-like sporangia and spores do not differ in appearance.
In the CIS, there are representatives of three families of conifers: pine - Pinaceae, yew - Tachaseaeikiparis - Cupressaceae.
The most common pine family includes genera:
Pine - Pinus. Long hard needles grow only on shortened shoots - two needles each: Scots pine - Pinus sylvestris, Crimean pine - Pinus pallasiana, or five needles each: Siberian cedar pine - Pinus sibirica, Weimu-tova pine - P i nus str obu s.
The first seed plants were the now extinct seed ferns, they gave rise to gymnosperms. Gymnosperms are ancient seed plants that are on the path of biological progress. They appeared on Earth over 350 million years ago, long before the appearance of angiosperms. Scientists believe that gymnosperms are descended from ancient multi-spore seed ferns that have not survived to this day. Seed fern prints are found in the deep layers of the earth's crust.
Pine branch structure
Pine branch
The structure of the female pine cone
In spring, small reddish buds can be seen on the tops of young shoots. These are female cones. The female cone consists of an axis, or rod, on which scales are located. On the scales of female cones, they are not protected by anything, as naked (hence the name - gymnosperms), ovules lie, an egg cell is formed in each of them.
The structure of the female pine cone
The structure of the male pine cone
On the same branches on which the female ones are located, there are also male cones. They are located not at the top of the young shoot, but at their base. Male cones are small, oval, yellow and in close groups.
The structure of the male pine cone
Each male bump consists of an axis on which the scales are also located. On the underside of each scale there are two pollen sacs, in which pollen matures - a collection of dust particles, in which male sex cells - sperm cells - are later formed.
The structure of a mature pine cone
Fertilization in pine occurs a year after the pollen hits the female cones. And the seeds spill out six months later, at the end of winter. By this time, the mature female cone becomes brown in color and reaches 4-6 cm.
Structure mature bumps pine trees
When the scales of a mature female cone move apart, it becomes clear that the seeds lie in pairs on the upper side of the scales, at their base. The seeds lie open, bare. Each pine seed is equipped with a transparent membraney wing, which allows it to be carried by the wind.
The process of pollination and fertilization in pine. (Development cycle)
Reproduction: sexual - by seeds.
Reproduction is carried out in two stages: the pollination process and the fertilization process.
Pollination process
- The pollen settles on the ovules of the female cone.
- The pollen enters the ovule through the pollen duct.
- The scales are closed and glued together with resin.
- Preparation for fertilization.
- Pollen, germinating, forms sperm and pollen tube.
Fertilization process
Fertilization occurs in the ovule 12 months after pollination.
- The sperm fuses with the egg, resulting in the formation of zygote.
- From the zygote develops embryo.
- Of all the ovules - seed.
The cone grows and gradually lignifies, its color becomes brown. The next winter, the buds open and the seeds spill out. They can be dormant for a long time and germinate only in favorable conditions.
Pine seedlings look very peculiar when they just emerged from the seed. These are small plants with a stem shorter than a match and no thicker than an ordinary sewing needle. At the top of the stem is a bunch of very thin cotyledon needles radiating in all directions. Pines have not one or two of them, like flowering plants, but much more - from 4 to 7.
Sprout of pine seed
Thus, plants belonging to the gymnosperm division differ from all other plants in that they produce seeds. Internal fertilization, the development of the embryo inside the ovule and the appearance of the seed are the main biological advantages of seed plants, which made them able to adapt to terrestrial conditions and achieve a higher development than seedless higher plants.
Scots pine dominates in the life cycle sporophyte- an adult tree, including: root, trunk, branches(elongated shoots), shortened shoots, leaves, male and female bumps.
Rod root system pine reaches a depth of 20-30 m and can enter into symbiosis with the mycelium (body) of fungi, for example, butter, creating mycorrhiza(mushroom root). Hyphae (outgrowths of the mycelium) braid the pine roots from the tips to the suction zone and penetrate inside, connecting to the conducting bundles. By absorbing organic matter from the plant, the fungus supplies water with minerals to the plant.
Trunk - a vertical lignified stem reaches a height of 30–40 m. Branches (elongated shoots) on the trunk are arranged in whorls, covered with sessile, spirally arranged brown scaly leaves and end in ovoid, conical, brown buds. In the sinuses of scale-like leaves develop shortened shoots, of which two leaves grow - needles... A pair of Scots pine leaves, 3–8 cm long, 1.5–2 mm thick, covered with a sheath at the base, functions (lives) for 3–5 years and falls off along with a shortened shoot.
Mens bumps- spore-bearing spikelets (strobila), formed in spring at the base of young elongated shoots. They are collected on a common axis. Each individual cone 8-12 mm long, yellow or color pink, consists of a short rod ( axes), on which reduced spore-bearing leaves are spirally located - microsporophylls... On the underside of microsporophylls there are two microsporangia... In microsporangia - pollen chambers, as a result of the division by meiosis of diploid cells of sporogenic tissue, haploid microspores... In turn, microspores divide by mitosis and form a four-cell male gametophyte – pollen... A pollen grain includes vegetative, generative(antiridial) and two thawed cells. The thawed cells are reserve, therefore, lagging behind in growth after some time, they give their resources to the development of generative and vegetative cells, quickly degenerate and disappear. Pollen cells are surrounded by two shells - outer, thick - exine and inner, thin - intina. In two places, the exine does not grow together with the intina, forming swellings - air bags.
Female cone bumps, 3-7 cm long, appear on the tops of elongated shoots singly or in a group of 2-3 pcs. Consist of axes, on which spirally located integumentary and seed scales - megasporophylls(female spore-bearing leaves). On the upper side of the seed scales, at their base, there are two seed bud, covered with integumentary scales. The seed bud is a megasporogenic tissue - nucellus surrounded by integumentary tissue - integument... At the apex of the seed germ, facing the axis of the cone, a hole remains in the integument - the pollen passage ( micropyle).
In the spring (in May), after the pollen has matured, the microsporangia of male cones open and the pollen is carried by the wind. Pollination- This is the process of getting pollen on the micropyle of seed buds. During pollination, the scales of female cones are wide open. The pollen is carried by air currents (wind) between the scales, adheres to the sticky liquid that is released from the micropyle. Due to the drying of the sticky liquid, pollen is drawn through the pollen inlet to the nucellus. After pollination, the micropyle overgrows, the scales of the female cone close, and the entire cone from the outside is sealed (filled) with resin. After hitting nucellus vegetative cell pollen grows into it pollen tube. Generative the cell enters the vegetative cell and moves in its apical part. For the next 13 months, the pollen tube slowly grows into the nucellus, in the direction of the future female gametophyte.
Rice. 40. Diagram of the life cycle of Scots pine
Rice. 41. Life cycle Scots pine
One month after pollination, one cell of nucellus - archesporial cell divides meiosis forming four haploid megaspores... Three of them die off, and the fourth megaspore farthest from the micropyle begins to grow. Its development in megagametophyte(female gametophyte) begins six months after pollination and requires another six months to complete its formation. During this time, the cell of the megaspore by mitotic division increases the number of its nuclei up to about 2000 pieces. At 13 months after pollination in the megaspore occurs cytokinesis- division of a multinucleated cell by cell walls, which localize the nuclei in individual cells. The formed haploid tissue is called endosperm... At 13–15 months after pollination, two or three reduced archegonia with oocytes In the middle. The endosperm with two archegonia is female gametophyte(overgrowth).
During the formation of the female gametophyte pollen tube(vegetative cell) grows through nucellus and endosperm, enters one of the archegonia. To this moment generative a pollen cell inside a vegetative cell (pollen tube) divides into two daughter cells - sterile(leg cage) and spermatogenic(body cell). After which the spermatogenic cell is divided into two sperm... The pollen tube with two sperm in the middle is completely developed male gametophyte... Having penetrated into the archegonia and reaching the ovum, the apical part of the cell wall of the pollen tube is destroyed, the cytoplasm flows into the archegonia cavity, and one of the sperm combines with the ovum, forming zygote, the other sperm dies. The fertilization process takes place approximately 13-15 months after pollination. Usually fertilized eggs (zygotes) of all archegonia are fertilized and begin to develop into embryos (polyembryology), however, as a rule, only one embryo is fully formed.
The next six months (6 months) after fertilization, the formation of seed from the seed germ: the zygote develops into embryo, endosperm remains as a storage tissue of the seed, the integument forms seed shell with pterygoid outgrowth, nucellus is spent on development endosperm and embryo... Black Scots pine seeds with a diameter of 4-5 mm, with a membranous pterygoid outgrowth of the seed coat 12-20 mm long, fully ripen in November-December, 18-21 months after pollination. Female cones, when ripe, become dull from gray-light brown to gray-green; open (wide open their scales) from February to April and soon fall off.
Angiosperms or Flowering plants - department of higher seed plants, a feature of which is the presence flower- the organ of sexual reproduction, in which the fruit leaves (pistil) contain seed buds. Another feature of angiosperms is the formation of a seven-celled female gametophyte in the seed germ - embryo sac and fertilization of two cells in it (an egg and a central diploid cell) - double fertilization... The angiosperms department has more than 250 thousand plant species.
| pine seed (seed germ) ↓ | |
| Pine ( adult plant, sporophyte) | |
| male bumps ↓ | female cones ↓ |
| sporangia ↓ | ovules (cones on the scales, carry sporangia) ↓ |
| meiosis (many small spores - microspores, all develop) ↓ | meiosis (4 large spores - megaspores, only one develops) ↓ |
| male outgrowth - gametophyte (pollen grain) ↓ | female outgrowth gametophyte (endosperm with 2 archegonia) ↓ |
| pollen is carried by the wind to the ovule, germinates, forming a pollen tube ↓ | eggs (one in each archegonia) |
| 2 sperm (delivered to the egg through the pollen tube) |   |
| zygote (one sperm (n) fertilizes one egg (n)) ↓ | |
| seed (seed germ) |
In the spring, at the base of young shoots, yellow-green male bumps... Male cones form pollen grains consisting of two cells - vegetative and generative... The generative cell is divided into two male gametes - sperm. Female cones collected in 1-3 at the ends of young shoots. Each cone is an axis from which two types of scales extend: sterile and seed. On each seed scale, two ovules are formed on the inside. In the center of the ovule, the endosperm develops, which is the female gametophyte. The endosperm develops from the megaspore, two archegonia are formed in its tissue. The pollen is carried by the wind, gets on the female cones and the ovule penetrates to the pollen duct. A sticky liquid is released from the pollen passage, and when it dries, the pollen is drawn into the ovule. When the dust particles fall on the female cones, the scales close and stick together with resin: at this time, the ovules are not yet ready for fertilization. Between pollination and fertilization in a pine, about a year passes. The vegetative cell of the pollen grain grows into the pollen tube, which reaches the archegonia. At the end of the pollen tube there are two sperm: one of them dies, and the other fuses with the egg of one of the archegonia. The embryo develops from the formed zygote.
Gymnosperms are higher seed plants that do not have flowers and do not produce fruits. Their seeds are located openly on the inner side of the scaly leaves, which form a cone. Gymnosperms are the first truly land plants, since no water is needed to fertilize them.
Flourishing gymnosperms refers to the Paleozoic and Mesozoic eras. In the process of evolution, gymnosperms evolved from ferns. The extinct transitional form is seed ferns. In appearance, these plants were close to ferns, but had ovules, which were located directly on the leaves, which gave reason to call this group Seed Ferns.
The predominant stage is sporophyte.
The stem (in the majority) is well developed, lignified. The stem includes bark, wood, and a poorly defined pith. The conductive tissue is represented by tracheids (evolutionarily more ancient structure than trachea). In the bark and wood of conifers, there are resin passages - intercellular spaces filled with essential oils and resin, which is secreted by the cells lining the canal. The resin protects the plant from the penetration of microorganisms and insects. The branching of the stem is monopodial, i.e. the apical shoot lasts all life. When the apical shoot is removed, the plant stops growing in height.
Coniferous leaves are small, scaly or needle-shaped called needles. They usually stay on the tree for 2-3 years. The needles are covered with cuticles. The stomata are deeply embedded in the leaf tissue, which reduces water evaporation.
The root system is usually pivotal. The main root is well expressed, penetrates deeply into the soil. Short lateral roots often contain mycorrhiza.
Gymnosperms are better adapted to life on land in many ways than spore plants. Their reproduction is not associated with the presence of moisture, since pollen is carried by the wind from the male sporophyte to the female. Fertilization takes place using a pollen tube. Due to the development of cambium and secondary wood, many gymnosperms reach large sizes.
Male cones are located among the needles at the base of young shoots. They are formed by microsporophylls (scales), which each carry 2 microsporangia (pollen sacs), in which spores develop. Male bumps are greenish yellow in color.
Female cones are located on the tops of other young shoots. They are brown or red-brown in color. Female cones consist of seed scales (megasporophylls) with 2 ovules and a sterile covering scales. Ovules (ovules) are formations from which seeds develop. Are located on the surface of the seed scales openly
2 - female lump
3 - seed scales with 2 ovules (top view)
4 - covering and seed scales (bottom view)
The life cycle of conifers (for example, pine).
Pine is a monoecious plant. In the spring, cones form on some of its shoots - male and female. The microspores of male cones are filled with microsporocytes (2n), which, after meiosis, form 4 haploid microspores each. Microspores are covered with a spore membrane and form a pollen grain, in which a male gametophyte is formed, which includes 1 vegetative and 1 generative cells. The spore membrane forms two air sacs, which facilitates the transport of pollen by wind over long distances.
· A - male lump;
· B - microsporophyll (1) with microsporangia (2);
· B - pollen: 3 - vegetative cell; 4 - generative cell; 5 - two air bags
After the rupture of the microsporangium wall, the pollen grains are scattered by the wind and fall on the female cones.
Megasporangium is a part of the ovule, covered with integument (integument) and attached to the seed scales (megasporophylls) with the help of a pedicle.
A - female cone
a - covering scales
b - seed scales
c - ovules on seed scales
1 - seed coat from below
2 - seed scales on top,
3 - ovule in section (inside megasporangia, inside which archegonia, outside covered with integument)
Megasporangium includes only one megasporocyte (2n), which after meiosis forms 4 haploid spores, three of which are reduced. The remaining megaspora forms the female gametophyte, which does not leave the megasporangium. Archegonia containing eggs are formed on the gametophyte.
Pine pollination occurs in late May - early June. Once on the ovule, the pollen grain sticks to a sticky liquid, which evaporates and pulls it into the ovule. The pollen grain germinates: a pollen tube is formed from the vegetative cell, 2 sperm from the generative cell (by mitosis). Sperm are passively transported to archegonia via the pollen tube. One sperm fertilizes the egg, the second dies.
The zygote formed after the fusion of the germ cells gives rise to the embryo, and the ovule - the seed. The seed consists of:
Embryo (2n)
Seed coat (2n) - formed from integument
· Stock of nutrients - endosperm (n) - is formed from the body of the gametophyte.
The developing embryo contains a root, a stalk, several cotyledons (germ leaves), and buds. Pine seeds ripen by the fall of next year. Usually in winter, lignified seed scales diverge, and seeds with pterygoid appendages are carried by the wind. Once in favorable conditions, the seeds germinate, giving rise to a sporophyte - a large leafy plant.
Pine- light-loving plant, undemanding to the soil. It grows on sands, rocks, swamps. Depending on the place of growth, it mainly develops either the main root or a system of lateral roots. Roots well, which helps to consolidate the soil. Pine growing in the forest can reach up to 40 m in height. It has a straight trunk covered with reddish-brown bark. A low, thin trunk is found in pine growing in a swamp. The pine tree has a lifespan of 350-400 years.
Spruce unlike pine, it is a shade-tolerant plant. The spruce develops a dense pyramidal crown. Its lower branches usually do not die off, but remain, so the spruce forests are dark. Spruce is more demanding on the surrounding conditions and grows on more fertile and sufficiently moist soils. Its root system is less developed than that of pine, and is located more superficially, so strong winds can "pull out" the tree by its roots. Spruce leaves - needles - needle-like, located singly on the shoots and stored on the tree for 7-9 years. If pine cones are 4-5 cm long, then in spruce they are 10-15 cm long and develop within one year. Reproduction in spruce occurs in the same way as in pine. Its life span is 300-500 years.
Conifers also include larch... It can withstand severe frosts in Siberia and Yakutia. Its needles fall off for the winter, which explains its name.
It is distinguished by its exceptional durability sequoia, or mammoth tree. The duration of her life is 3-4 thousand years.
In pine and mixed forests, on dry hills, common juniper is found - an evergreen shrub with needle-like leaves. Its peculiar cones have non-expanding scales and resemble fleshy bluish berries.
The value of conifers .
Like all green plants, they form organic matter, absorb carbon dioxide and release oxygen. Coniferous forests delay snow melting and enrich the soil with moisture. Pine releases phytoncides - volatile substances with antibacterial properties. They preserve the structure of the soil and protect it from destruction (pine).
Man uses conifers as a valuable building and ornamental material ("ship pines", "mahogany" - sequoia wood, decay-resistant larch wood). Spruce wood is used to make paper. Turpentine, rosin, sealing wax, varnishes, alcohol, and plastics are obtained from conifers. From the seeds of Siberian cedar pine they produce edible oil... Cedar pine seeds are edible. Some inhabitants of the forest feed on conifer seeds. Juniper cones are used as medicinal product... Many conifers are cultivated as ornamental plants
### Homework
1. Seeds of Siberian pine are called pine nuts. Explain if the name is scientifically correct.
2. Scientists have found that coniferous trees(spruce, pine) are less resistant to air pollution from industrial gases than deciduous trees. Explain what is the reason for this phenomenon.
· Various harmful substances settle on the leaves.
· In deciduous plants, leaves fall off annually, and harmful substances are removed with them, in conifers, leaves live for 3-5 years or more, therefore, harmful substances are not removed and lead to poisoning of the body.
3. Give a detailed answer to the question. What are the characteristics of conifers?
4. Why in August in the coniferous forest under the trees you can see a lot of fallen needles, and in the deciduous forest there are almost no fallen leaves? How does this affect soil fertility?
· The needles contain many resinous substances that impede their decomposition by microorganisms.
· In addition, in the coniferous forest, under shade conditions, the temperature is lower and the decomposition rate is low.
· Due to the slow decomposition and leaching of organic matter, the soil in the coniferous forest contains little humus.
5. What chromosome set is typical for the cells of the pollen grain and spermatozoa of pine? Explain, from what initial cells and as a result of what division these cells are formed?
6. Why do pests live more on old, diseased pine trees?
Answer:
· A lot of resin is released on young trees,
· the resin contains turpentine, which repels pests.
· Older trees are a more comfortable refuge.
7. What are the advantages of plant propagation by seeds compared to spores?
8. What is the difference between a pine seed and a fern spore and what are their similarities?