REMEMBER
Question 1. How do plants reproduce?
All types of breeding can be divided into two main groups - vegetative propagation and generative. About vegetative reproduction, it is enough to say only that this is reproduction by lateral shoots, buds, roots, tubers, that is, a young plant is separated from an adult plant. Generative reproduction is divided in turn into sexual, asexual and seminal. Asexual reproduction, that is, reproduction by spores is characteristic of ferns and mosses, as well as algae. Other higher plants reproduce sexually, that is, they have special organs in which fertilization, pollination occurs, that is, the fusion of male and female germ cells. A type of sexual reproduction is seed reproduction, when a seed is formed, from which a new plant subsequently grows.
Question 2. What do you know about animal reproduction?
Multicellular animals reproduce mainly sexually, but there are groups (especially among the lower invertebrates) that reproduce very successfully asexually.
Asexual reproduction of multicellular organisms is an increase in the number of individuals formed from somatic (nonsexual) cells. Among animals, it is completely absent in primary cavity worms and mollusks. In arthropods, vertebrates, polyembryony can be attributed to asexual reproduction, that is, asexual reproduction at the stages of embryonic development.
Sexual reproduction in animals takes several forms. Firstly, bisexual reproduction can be distinguished, which exists in the form of dioeciousness and hermaphroditism, and secondly, virgin reproduction, or parthenogenesis.
Question 1. What is reproduction?
Reproduction is the reproduction of similar organisms, an important property of living things.
Question 2. What are the features of asexual reproduction?
The most ancient and simple way of reproduction is asexual. It is carried out by division, spores and vegetative organs. Only one organism participates in asexual reproduction. With this method of reproduction, the offspring retains the greatest similarity with their parents.
Question 3. Why do many plants reproduce predominantly asexually?
Vegetative reproduction is widespread in plants. It occurs due to the separation of vegetative organs or their parts from the mother's body and the development of new ones from them, daughter plants... During vegetative reproduction, a new individual is formed from a part of the body of the mother's body, so it inherits all of its characteristics.
1. Review Figure 81 and outline a story about vegetative propagation of flowering plants. Find examples.
1. Methods of vegetative propagation and their diversity
2. Reproduction separate parts body
3. What plants grow vegetatively?
2. Using Internet sources, popular science magazines, books, textbook text, prepare a message on the topic "Reproduction through spores."
Plant propagation is physiological process reproduction of similar organisms, ensuring the continuity of the existence of the species and its dispersal in the environment.
Asexual reproduction in a number of plants (algae, mosses, ferns) is carried out using spores. The spore is one cell, protected by a thick membrane from drying out and mechanical damage. Disputes are formed in special formations - sporangia. Being very light, spores are carried far by the wind. V favorable conditions spores germinate and new organisms are formed from them. Plants usually form a huge number of spores, but not all of them develop new plants. Many spores end up in unfavorable conditions and die.
In the process of evolution about 400 million years ago, from multicellular green algae, rhinophytes arose - the first higher plants that multiply by spores, which gave rise to all modern higher spore and seed plants. This is an extinct group of plants. V life cycle of higher spore plants, as in some algae, individuals of asexual and sexual generations alternate, which reproduce, respectively, asexually and sexually. In the full life cycle, which ensures the continuity of the life of organisms, there is an alternation of gametophyte (sexual) and sporophyte (asexual generation). On the sporophyte, the organs of asexual reproduction are formed, on the gametophyte, the sexual organs.
Higher spore plants after reaching land in the course of evolution, they underwent metamorphoses in two directions. Thus, two large evolutionary groups were formed - haploid and diploid. The first branch includes mosses, in which the gametophyte is better developed, and the sporophyte occupies a subordinate position. The diploid branch includes ferns, horsetails and moss. Their gametophyte is reduced, and looks like an outgrowth.
From the spores that form individuals of the asexual generation, individuals of the sexual generation grow. They have special male and female genital organs, in which male and female reproductive cells (gametes) develop - motile spermatozoa and immobile eggs. For fertilization, the sperm must enter the external environment and fertilize the egg, which is inside the female genital organ. Water is needed to move the sperm. An embryo is formed from a fertilized egg. It germinates and turns into an asexual generation, which reproduces by spores.
THINK!
Why do many cultivated plants propagate vegetatively?
During vegetative propagation, the properties of the mother plant are fully preserved. Here, neither pollination can affect, nor the methods of pruning, fertilization, and so on. Whereas sowing with seeds from a cultivated plant gives a whole fan of differences from the original plant.
Asexual reproduction is such a reproduction of organisms in which there is no participation of another individual, and reproduction of their own kind occurs by separating several or one cell from the mother's organism. A single parent takes part in this process. cells are fully consistent with the original maternal.
Asexual reproduction is extremely simple. This is due to the fact that the organization of the structure of unicellular organisms is also relatively simple. Organisms with this method of reproduction reproduce their own kind very quickly. Under favorable conditions, the number of such cells doubles every hour. This process can continue indefinitely until a random change occurs, the so-called mutation.
In nature, such reproduction occurs in both plants and
Asexual reproduction of organisms
Simple division is also observed in animals, for example, in ciliates, amoebas and some algae. First, the nucleus in the cell divides in half through mitosis, and then a constriction is formed, and the parent is divided into two parts, which are daughter organisms.
In animals, asexual reproduction was preserved only in some forms: sponges, coelenterates, tunicates. In these organisms, a new individual is obtained as a result of budding or division, after which the part separated from the parent organism is completed to the whole. In some cases, body parts have the ability to develop into a separate organism in animals. A whole hydra, for example, can develop from a two-hundredth part. With asexual reproduction, newly created individuals originate from several cells or one through mitotic divisions, receiving the same hereditary information that the cell of the mother's body possessed.
Asexual reproduction of plants
Such a way of reproduction is widespread in flora... There are a number of plants that reproduce well with tubers, cuttings, cuttings and even leaves, which allows the vegetative organs of the parent plant to be used for growing new organisms. This type of asexual reproduction is called vegetative, and it is inherent in highly organized plants. An example of such reproduction can be considered one that occurs with a mustache, for example, in strawberries.
Spore formation is asexual reproduction that occurs in many plants, for example, algae, ferns, mosses, fungi at some stage of development. In this case, special cells take part in the reproduction mechanism, often covered with a dense membrane, which protects them from adverse effects. external environment: overheating, cold, drying out. As soon as favorable conditions arise, the shell of the spore bursts, the cell begins to divide repeatedly, giving life to a new organism.
Budding is a method of reproduction, when a small part of the body is separated from the parent, from which the daughter organism is later formed.
A set of individuals that descended from one common ancestor using this type of reproduction is called clones in biology.
Asexual reproduction is widely used in agriculture in order to obtain plants with a set of necessary traits that are useful for human life. Strawberries are spread with long "mustaches", shoots, and trees - by cuttings. Scientists are researching reproductive mechanisms in order to learn how to control them and guide their development. the necessary hereditary information is first multiplied, and then the necessary whole plant is grown from them.
Lecture 6. Reproduction of plants
Reproduction is an essential property of living organisms to reproduce their own kind. Thanks to reproduction, the continuity and continuity of life is ensured. There are two main forms of reproduction: asexual and sexual.
Asexual reproduction. Reproduction, in which one organism takes part, there is no formation and fusion of gametes, no fusion genetic material in any form... This is the most ancient form of reproduction, widespread in all groups of plants, occurs by mitotic division or with the help of spores, a special form of asexual reproduction is vegetative reproduction.
Division ... Reproduction by division is characteristic of unicellular algae. Division occurs through mitosis, as a result, individuals are formed that are genetically identical to each other and to the mother's body.
Reproduction by spores . Plant spores are reproductive, unicellular formations that serve to form new individuals... In most algae living in water, spores are mobile, since they have flagella. Such disputes are called zoospores... Have land plants and they do not have mushrooms special devices for active movement. Spores are formed in the organs of asexual reproduction - sporangia or zoosporangia. In algae, almost any cell can become a sporangium, in higher plants sporangium is a multicellular organ. In plants, spores are always haploid. If they arise on a diploid plant, then their formation is preceded by meiosis, if on a haploid plant, mitosis. The spores resulting from meiosis are genetically unequal, the organisms that develop from them are genetically unequal.
The plant on which spores form is called a sporophyte. If the spores are morphologically indistinguishable, then the plants that form them are called homosporous, heterosporous plants are plants that form spores, always differing in size and physiological characteristics. Microspores - smaller spores that form in microsporangia, from which they grow male gametophytes (plants forming male gametes ). Megaspores - larger spores that form in megasporangia, grow out of them female gametophytes ... Diversity is more common among higher plants (some lyes, ferns, all gymnosperms and angiosperms).
Reproduction by spores is of great biological importance - as a result of meiosis, a recombination of genetic material occurs, new combinations of gene alleles appear in disputes, which fall under the control of selection; usually in plants, spores are formed in huge quantities, which provides a high intensity of reproduction. Due to their small size and lightness, the spores are carried over long distances, ensuring the dispersal of plants; the dense shell of the spore serves reliable protection from adverse environmental conditions.
Vegetative propagation of plants - this is an increase in the number of individuals due to the separation of viable parts of the vegetative body and their subsequent regeneration (restoration to the whole organism). This method reproduction is widespread in nature. Both algae and higher plants reproduce in a vegetative way.
Vegetative reproduction happens natural and artificial ... Thanks to natural vegetative reproduction in nature, there is a rapid increase in the number of individuals of the species, their dispersal and, as a result, success in the struggle for existence. Natural vegetative reproduction occurs in several ways: by fragmentation of the maternal individual into two or more daughter ones; destruction of areas of ground-creeping and lodging shoots (lyes, gymnosperms, flowering); with the help of special structures specially designed for vegetative propagation (tubers, bulbs, rhizomes, corms, axillary buds, adventitious buds on leaves or roots, brood baskets of bryophytes, etc.).
Artificial vegetative reproduction is carried out with the participation of humans during cultivation cultivated plants... Artificial vegetative reproduction has a number of advantages over seed: it provides offspring that retain the characteristics of the parent organism, accelerates the generation of offspring, and allows a large number of offspring to be obtained. In addition, with the help of vegetative propagation, clones of those plants that form non-viable seeds or do not form them at all can be reproduced.
Vegetative propagation methods. Plants can be propagated by vegetative organs - by dividing the whole plant into parts, aboveground and underground shoots, leaves, roots.
Fragmentation the division of an individual into two or more parts is called, each of which regenerates into a new individual (Fig. 34). Such reproduction is typical for filamentous and lamellar algae (scraps of filaments or parts of the thallus), some flowering plants (for example, Canadian Elodea). Only female specimens of Elodea, unable to form seeds due to the lack of male plants and fragmentation was the only way to reproduce.Division of bushes. Currants, gooseberries, primroses, rhubarb reproduce well in parts of the bushes. The plant is dug up, divided into parts and planted separately from each other. The bushes are usually divided in spring or late summer.
Reproduction by aerial shoots.
Mustache ... In agricultural practice, strawberries and strawberries are propagated with a mustache. In the nodes of the whiskers, lateral buds and adventitious roots are formed. After the internodes dry up, the plants are isolated. In nature, plants such as creeping buttercup and saxifrage reproduce with whiskers.
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Stem cuttings. Stem cutting is an aerial shoot site. Stem cuttings propagate grapes, currants, gooseberries, decorative species spirea, red pepper, eggplant and others. For reproduction, cuttings are taken from 2-3 to 6-8 cm long, consisting of one internode and two nodes. At the top node, leaves are left (if the leaf blades are large, then they are cut off by half). Cuttings are planted in special greenhouses, and after rooting - in open ground.
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a plot of bark and wood (peephole) grafted onto another plant is called graft. Rootstock- a plant or a part thereof on which the vaccination was carried out. Vaccination allows you to use root system rootstock for preserving or propagating a certain variety, replacing a variety, obtaining new varieties, accelerating fruiting, obtaining frost-resistant plants, repairing or rejuvenating old mature trees.
There are many methods of grafting, but all of them can be reduced to two main types: grafting by rapprochement, when the scion and rootstock remain on their roots, grafting with a separated scion, when only the rootstock has roots.
The most common methods of vaccination are as follows (Fig. 38). Inoculation into cleft or semi-cleavage... Apply if the scion is thinner than the rootstock. The cross section of the rootstock is completely or partially divided and the scion is inserted into it, cut obliquely from both sides.
Bark grafting. The graft is also thinner than the rootstock. A horizontal cut is made on the rootstock under the stem node, the bark is incised in the vertical direction and its edges are carefully turned off. A cut in the form of a half-cone is made on the scion, inserted under the bark, clamped with bark lapels and tied.
Copulation... It is used if the scion and rootstock are of the same thickness. On the scion and rootstock, make oblique cuts and combine them, ensuring the tightness of the connection.
Budding... Inoculation of the bud-eye. A T-shaped incision is made on the stock, the edges of the bark are folded back, and a bud is inserted behind the bark with small plot wood and tightly bandaged.
Reproduction by underground shoots.
Tuber ... Potatoes and Jerusalem artichoke are the most famous of the agricultural plants propagated by tubers. They can be propagated by planting whole tubers or parts thereof with eye buds. Tubers, as a repository of nutrients, are formed in such wild plants as feeding, weekly.
Rhizome ... In agriculture, rhizomes propagate rhubarb, mint, asparagus, bamboo, in ornamental gardening - lily of the valley, iris and others. They easily multiply by dividing the rhizomes into parts, each of which must contain a vegetative bud.
A large number of rhizome plants, primarily cereals, live in forests, steppes, and meadows. Rhizomatous plants include wheatgrass, timothy, whiteus, kupena, oxalis, field horsetail and others. wild plants... In many, the rhizomes branch, and when the old parts die off, new plants are isolated.
Bulb ... In agricultural practice, onions, garlic, ornamental plants: tulips, daffodils, hyacinths and others. In nature, many plants reproduce by bulbs: tulips, goose onions, scrub, snowdrop, etc. Vegetative propagation of bulbous plants is carried out by overgrown adult bulbs, children, individual scales.
Corm ... The reserve nutrients of the corm are used up for flowering, but by the end of the season a new corm is formed. In addition, one or more corms may form - fleshy buds developing between the old and new corms. Corms include gladiolus, crocus.
Root tubers ... They are thickenings of lateral roots. In ornamental gardening, dahlias and sweet potatoes are propagated by root tubers. When breeding dahlias, it is necessary to take root tubers with the base of the stem bearing the buds, since the root tubers do not form buds. Root tubers are propagated by the spring cleaver, two-leaved lyubka.Reproduction by root suckers. Root offshoots - shoots arising from the adventitious buds on the roots (Fig. 36). Root offspring reproduce plants that easily form adventitious buds on the roots: cherry, plum, raspberry, lilac, aspen, sow thistle, thistle field, etc.
Root cuttings. The root cutting is part of the root. They breed species, on the roots of which adventitious buds easily develop: horseradish, raspberries, cherries, roses. Root cuttings are harvested in autumn, less often in spring. For this, lateral roots of the first order are used at the age of 2-3 years. The length of the cuttings is up to 10-15 cm, the diameter is 0.6-1.5 cm.The cuttings are planted in the soil to a depth of 2-3 cm.Many wild plants propagate by cuttings: willow, poplar, aspen, dandelion
Reproduction by leaves.
Whole leaves. Many flowering plants propagated by leaves, for example saintpaulia, begonias. It is enough to put the leaf in water, adventitious roots and adventitious buds appear, after a while the plant is transplanted into the soil.
Leafy cuttings. Sometimes even a part of a leaf is enough for vegetative propagation. In the royal begonia, a part of the leaf with a large vein is cut out, the sansevier leaf can be cut into several leaf cuttings and put in water.
Accessory buds on the leaves, kids ... In bryophyllum, adventitious buds are formed on the leaves, similar to small plants. Falling, they become independent plants.
Tissue culture. Tissue culture is the growth of plant cell groats on artificial media. Plant cells have the property totipotency- a single cell can develop into a normal plant using certain phytohormones. The tissue culture method allows you to obtain clones some higher plants. Cloning- obtaining a set of individuals from one maternal vegetative way. Cloning is used for the propagation of valuable plant varieties and for the improvement of the planting material.
Sexual reproduction. Sexual reproduction is associated with the formation of a special type of cells by plants - gametes. The plant on which the formation of gametes occurs is called gametophyte... The process of gamete formation is called gametogenesis... It takes place in special organs - gametangia... In homosporous plants, the gametophyte is usually bisexual: it bears both female and male gametangia. In plants of different spores, a gametophyte with male gametangia develops from microspores, and a gametophyte with female gametangia from megaspores. Gametes of plants are formed mitotically, meiosis occurs after the formation of a zygote ( zygotic reduction) - many algae, or during the formation of spores ( controversial reduction) - in diploid algae and higher plants. In animals, meiosis occurs during the formation of gametes ( gametic reduction).
Sexual reproduction has several advantages over asexual reproduction. First, when gametes merge, an organism is formed with a unique double set of alleles of genes obtained from parents with different genotypes; an organism with a unique genotype is formed. As a result of selection, individuals will survive, whose genotype allows them to adapt to the given environmental conditions, even if these conditions change.
Secondly, mutations that change genes are more often recessive and harmful in given environmental conditions. The diploid set of genes allows the emerging recessive alleles to persist due to the presence of dominant alleles of these genes. Each diploid organism contains hundreds, thousands of genes in a recessive state, as the sponge is saturated with water, and the genotype is saturated with them, they are passed on to the next generation and gradually spread throughout the population. A mutation will manifest itself if both gametes carry a given recessive allele of the gene, and by this time the environment may have changed, and this mutation may be useful. This is how mutations accumulate and spread.
Gametes are always haploid. When the male and female gametes merge, a diploid zygote is formed, from which a new organism develops. The process of gamete fusion is called fertilization... The essence of the sexual process is the same for all living organisms, and its forms are diverse. There are the following types of sexual process: hologamy, conjugation, isogamy, heterogamy and oogamy (Fig. 39).
Hologamia ... Hologamy is the fusion of haploid unicellular, externally indistinguishable organisms with each other. This type of sexual process is characteristic of some unicellular algae. In this case, not gametes merge, but whole organisms acting as gametes. The resulting diploid zygote usually immediately divides meiotically ( zygotic reduction) and 4 daughter haploid unicellular organisms are formed.
Conjugation. A special form of the sexual process is conjugation, which is characteristic of some filamentous algae. Separate haploid cells of filamentous thalli located close to each other begin to form outgrowths. They grow towards each other, connect, the partitions at the junction dissolve, and the contents of one cell (male) pass into another (female). As a result of conjugation, a diploid zygote is formed.
Isogamy. With isogamy, gametes are morphologically similar to each other, that is, they are the same in shape and size, but physiologically they are of different quality. This sexual process is characteristic of many algae and some fungi. Isogamy occurs only in water, for movement in which gametes are equipped with flagella. They are very similar to zoospores, but smaller in size.
Heterogamy. With heterogamy, there is a fusion of mobile germ cells, similar in shape, but differing in size. The female gamete is several times larger than the male gamete and less mobile. Heterogamy is characteristic of the same groups of organisms as isogamy and also occurs in water.Oogamy. It is characteristic of some algae and all higher plants. The female gamete - the ovum - is large and motionless. Have lower plants formed in unicellular gametangia - oogony, in higher plants (excluding angiosperms) - in multicellular archegonium... The male gamete (sperm) is small and mobile; it is formed in fungi and algae in unicellular organisms, and in higher plants (excluding angiosperms) in multicellular gametangia - antheridia... Sperm cells can only move in water. Therefore, the presence of water - required condition for fertilization in all plants, with the exception of seed. Most seed plants male gametes have lost their flagella and are called sperm.
Key terms and concepts
1. Asexual reproduction. 2. Plant spores. 3. Zoospores. 4. Sporophyte. 5. Male and female gametophytes. 6. Microspores and megaspores. 7. Vegetative reproduction. 8. Graft. 9. Rootstock. 10. Gametangia. 11. Zygotic reduction. 12. Spore reduction. 13. Gametic reduction. 14. Hologamia. 15. Isogamy. 16. Heterogamy. 17. Oogamy. 18. Conjugation. 19. Oogonia. 20. Archegonia. 21. Antheridia. 22. Totipotency.
Essential Review Questions
1. Reproduction of plants by division.
2. Reproduction by spores.
3. Natural vegetative reproduction.
4. Reproduction by fragmentation and division of bushes.
5. Reproduction by aerial shoots (whiskers, layering, stem cuttings).
6. The main methods and features of reproduction by grafting.
7. The main methods of reproduction by ground shoots.
8. The main methods of propagation by roots.
9. The main methods of plant propagation by leaves.
10. Reproduction by tissue culture.
11. Benefits of sexual reproduction.
12. Characteristics of the main types of sexual processes (chologamy, conjugation, isogamy, heterogamy, oogamy).
Reproduction- This is the reproduction of similar organisms, an important property of living things. Sooner or later, organisms die: some from old age, others from diseases, and still others fall prey to predators. However, with the death of each organism, the life of species on Earth does not stop. Thanks to reproduction, new generations of organisms appear to replace dying and dying individuals.
During reproduction, the number of individuals increases, the organisms spread to new places. Reproduction is associated with growth - an increase in mass and size and development - with internal and external changes that occur from the moment of formation to the death of an organism.
Distinguish between asexual and sexual reproduction. The most ancient and simple way of reproduction is asexual. It is carried out by division, spores and vegetative organs. Only one organism participates in asexual reproduction. With this method of reproduction, the offspring retains the greatest similarity with their parents.
Male and female individuals participate in sexual reproduction, fertilization occurs - the fusion of male and female germ cells. Therefore, during sexual reproduction, each organism inherits the properties of both parents.
Plant propagation... Plants have widespread vegetative propagation... It occurs due to the separation of vegetative organs or their parts from the mother's organism and the development of new daughter plants from them (Fig. 62). During vegetative reproduction, a new individual is formed from a part of the body of the mother's body, so it inherits all of its characteristics.
Rice. 62. Vegetative propagation of flowering plants
In flowering plants, vegetative reproduction in nature occurs with the help of all organs on which buds are formed - future shoots. Vegetative propagation allows plants to spread faster and occupy new areas.
Many weeds, for example dandelion, wheatgrass, thistle, reproduce vegetatively. It is very difficult to deal with them. Pulling a dandelion out of the soil will likely leave part of the root in it, from which a new plant will grow.
Some forest grasses reproduce with the help of long rhizomes, since seed reproduction is difficult for them due to the lack of pollinators, lack of light, etc. These plants include lily of the valley.
Algae can multiply by sections of threads, separation of a part of the body at the point of attachment to the ground. In mosses and ferns, young shoots can grow and separate from each other.
Some plants - algae, mosses, ferns - multiply by spores. A spore is one cell with a thick membrane that protects it from drying out and mechanical damage.
Usually a lot of disputes are formed. They are very small and light, so they are carried by the wind over long distances. Of the huge number of spores, only a few fall into favorable conditions and germinate, giving rise to a new organism. A significant part of them perish. Therefore, the formation of plants or fungi a large number the spore is an adaptation to the survival and preservation of the species.
Answer the questions
- What is reproduction?
- What are the features of asexual reproduction?
- Why do many plants predominantly reproduce asexually?
New concepts
Reproduction. Asexual reproduction. Vegetative reproduction.
Think
Why do many cultivated plants propagate vegetatively?
My laboratory
Vegetative propagation is used in urban greening, in agriculture. For example, gooseberries, currants, phloxes, daisies are propagated by dividing the bush; strawberries - whiskers, potatoes - tubers.
Often cuttings are used for reproduction - part of the stem, leaf, root, which develop into a new shoot. Stem cuttings propagate currants, tradescantia, pelargonium; root cuttings - rose hips, raspberries; leafy cuttings - begonia.
You can propagate by cuttings houseplants ficus, komus, etc. To do this, cut the cuttings with 3-4 leaves. Cut off the two bottom sheets (explain why). Plant the cuttings in a box with soil covered with moistened sand, at an angle of 45 °. Cover the cuttings glass jar to reduce water evaporation. After two to three weeks, roots form on the lower part of the cuttings planted in the soil. Transplant young plants into pots and care for them.
V recent times wide application in the national economy received another method of vegetative reproduction - from one cell or a piece of tissue. This is the so-called tissue culture method (Fig. 63). It allows for a relatively short time to small areas, even in a test tube, to obtain numerous offspring of a particular plant.
Rice. 63. Tissue culture method
Using the tissue culture method, it was possible to establish industrial production such a rare and valuable medicinal plant as ginseng. If in natural conditions Only by the age of 50, the mass of the ginseng root is about 50 g, then under artificial conditions this mass is obtained in about six to seven weeks.
Asexual reproduction is also typical for animals. In this case, the offspring is produced by one parent individual. Simplest form asexual reproduction of animals - division. It is characteristic of unicellular and some multicellular animals.
Asexual breeding method for freshwater hydra is by budding. Under favorable conditions, buds are formed on the body of the hydra, which grow and after a while are separated from the mother's body, turning into young hydras (Fig. 64).
Rice. 64. Asexual reproduction of freshwater hydra by budding
With asexual reproduction of plants, division of the parent individual and vegetative reproduction are possible.
Asexual reproduction is widespread in all plant groups. In its simplest form, with this type of reproduction, the parent is divided into two parts, each of which develops into an independent organism. This mode of reproduction, called division, is found, as a rule, only in unicellular organisms. In this case, the cell divides by mitosis.
Many multicellular organisms are also able to reproduce successfully by separating viable parts of the vegetative body, from which full-fledged daughter individuals are formed. This type of asexual reproduction in the plant world is often called vegetative. The ability to reproduce vegetatively is very characteristic of plants and fungi at all levels of their organization, as well as for some lower groups of animals. Such reproduction is characterized by the restoration of the whole organism from its part, called regeneration.
Often at the same time, plants reproduce by scraps or parts of the thallus, mycelium, or parts of vegetative organs. Many filamentous and lamellar algae, mycelium of fungi, lichen thalli freely disintegrate into parts, each of which easily becomes an independent organism. Some flowering plants that live in the water can also reproduce in this way. An example of a plant that reproduces exclusively vegetatively in Europe is the dioecious Elodea canadensis (Elodea canadensis), which came here from North America... At the same time, only female specimens were brought to Europe, unable to form seeds in the absence of male plants. Despite the absence of seed renewal, the plant reproduces extremely quickly and rapidly assimilates new habitats.
In practice Agriculture many methods have been developed for artificial vegetative propagation of cultivated plants belonging to a variety of life forms. So, many shrubs and perennial grasses reproduce by dividing the bush, rhizomes and root suckers. Onions, garlic, lilies, tulips, hyacinths, crocuses, gladioli and others reproduce successfully by bulbs and bulb-tuber, separating daughter bulbs, or "babies", from mother plants. In horticulture, forms of vegetative propagation with the help of cuttings and grafting are especially widespread.
A cut is a segment of a vegetative organ that serves for artificial vegetative reproduction. Cuttings can be stem, or shoot, but some plants can also propagate by leafy (begonia, lily) or root (raspberry) cuttings. A variety of cuttings is the propagation of trees and shrubs by layering. In this case, part of the shoot is first specially pressed against the soil for rooting and only then cut off. Layers are also found in nature, with the lodging of branches of fir, linden, bird cherry and other species capable of rooting in this way. Many fruit, woody and herbaceous ornamental plants are propagated by cuttings in open and closed ground. When propagating by cuttings, all the properties of the parent cultivated plant are preserved, which is very important, since during seed propagation, many characteristics specially selected by selection are easily lost.
Grafting is widely used in horticulture, when a stalk or just a vegetative bud of a plant with the desired properties, the so-called scion, is fused with a more powerful and unpretentious plant or stock. Grafting allows you to quickly multiply valuable plants and ensures their accelerated development, while fully preserving the right qualities... In this case, the grafted plant receives such valuable properties rootstock, as frost resistance, resistance to fungal diseases and unpretentiousness to soil fertility. More than 100 methods of vaccination have been developed. Many non-seed-forming varietals are propagated exclusively by grafting.
