The value of horsetails in human life, their role in nature. Horsetail world Horsetail breeding cycle

The development cycle of horsetail is dominated by sporophyte- an adult, perennial plant, consisting of rhizomes fixed in the soil adventitious roots. In the spring, from the buds of the rhizome to the surface of the soil grows spore-bearing, chlorophyll-free vertical the escape(stem) with a whorled arrangement of reduced (small) leaves, ending in a spore-bearing spikelet ( strobilus). The spore-bearing spikelet itself in its structure has axis, on which umbrella-shaped spore-bearing leaves (scutes on legs) are placed - sporophylls. On the lower side of the sporophylls, facing the axis of the strobilus, there are from 5 to 10 sporangia. In sporangia as a result of reduction division meiosis cells sporogenous tissue(2n) haploid, morphologically identical, but heterosexual disputes(male and bisexual). Spore shells have special outgrowths - elaters, which are twisted spirally around the spores when wet, and unfold when dry. This allows the spores to cling to each other and spread in groups. After maturation of the spores, the spore-bearing leaves of the strobilus open, the sporangia burst and the spores are carried by the wind. Due to the content of chloroplasts in spores, they quickly (within 3 weeks) lose their germination capacity. Getting on moistened silty soil, groups of spores germinate into chlorophyll-bearing gametophytes in the form of bladed plates fixed in the substrate rhizoids. Gametophytes reach sexual maturity 3-5 weeks after germination. On male gametophytes, smaller, are formed antheridia- male gametangia, in which polyflagellates are formed spermatozoa. On bisexual gametophytes, more dissected, archegonia(female gametangia) develop earlier than antheridia, which increases the likelihood of cross-fertilization. In order for spermatozoa to reach the eggs in the archegonium, water. On one gametophyte, several eggs can be fertilized at once, from which they develop in the future. embryos, there are young sporophytes. The embryos are attached with their feet to the tummy of the archegonium and receive the necessary nutrients for development from the gametophyte, forming a rudimentary root, stem and kidney. After formation, the germinal root begins to grow, becomes fixed in the soil, and the young sporophyte detaches from the gametophyte, which dies off after a while. After sporulation spring(spore-bearing) shoots die off and green rhizomes grow from the buds assimilation shoots. Assimilation shoots have a vertical stem with a whorled arrangement on it side branches And leaves below them. They perform the function of the formation of organic compounds in the process of photosynthesis and their accumulation in the rhizome. At the end of the growing season, assimilation shoots die off, leaving a rhizome that overwinters in the soil.

Rice. 34. Scheme of the life cycle of horsetail

Rice. 35. Life cycle of horsetail

Lycopsoid - department of higher spore plants, represented by 1200 species. They are characterized by the presence of a developed conducting system, root-shoot type of sporophyte structure and thallus structure of gametophytes, asexual reproduction by spores and vegetative reproduction by above-ground shoots.

What are the features of the structure and reproduction of horsetails (horsetails)?

Horsetails are perennial herbaceous plants with a jointed structure. Shoots are divided into nodes and internodes. The leaves are reduced to whole small plates. The function of photosynthesis is performed by the stem. Silica accumulates in horsetail cells, which makes the stem stiff. Horsetails reproduce by spores, which are formed in spore-bearing spikelets. Spore-bearing spikelets are formed either on special spore-bearing shoots (in horsetail), or on the tops of vegetative shoots (meadow horsetail, wintering horsetail). The spore-bearing spikelet consists of an axis on which sporangiophores are located. The sporangiophore consists of a stalk with a hexagonal plate. On the underside of the plate are sporangia. Spores are formed in sporangia. In dry weather, spores spill out. The gametophyte is formed from the spore. It has antheridia with spermatozoa and archegonia with eggs. After fertilization, a zygote is formed, and an embryo and a new plant develop from it.

Theory for preparation for block No. 4 of the Unified State Examination in biology: with system and diversity of the organic world.

Lycopsidae (Plyunidae)

Lycopsformes- one of the most ancient divisions of higher spore plants. At present, they are represented by a relatively small number of genera and species, the participation of which in the vegetation cover is usually insignificant. Perennial herbaceous plants, usually evergreen, resembling green mosses in appearance. They are found mainly in forests, especially coniferous ones.

There are about 400 species, but only 14 are common in Russia (club-shaped club, baranets, two-pointed club, etc.).

The structure of clubs

Lycopsoides are characterized by the presence of shoots with spiral, less often opposite and whorled leaves. The underground parts of the shoots in some lycopods look like a typical rhizome with modified leaves and adventitious roots, in others they form a kind of organ that carries spiral roots and is called a rhizophore (root bearer). The roots of the lycopsid are adventitious.

Nutrition and breeding of club mosses

sporophylls may be similar to ordinary vegetative leaves, sometimes differ from them. Among the lycopsids there are equally and heterosporous plants. Equosporous gametophytes underground or semi-underground, fleshy, 2-20 mm long. They are bisexual, saprophytes or semi-saprophytes, mature within 1-15 years. Gametophytes of heterosporous unisexual, non-green, usually develop within a few weeks due to the nutrients contained in the spore, and when ripe do not protrude or slightly protrude outside the spore shell. The genital organs are represented by antheridia and archegonia: in the former, two- or multi-flagellated spermatozoa develop, in the archegonia - eggs. Fertilization occurs in the presence of drip-liquid water, a sporophyte grows from the zygote.

sporophyte club moss is a perennial evergreen plant. The stem is creeping, branched, gives vertical branched shoots about 25 cm high, densely covered with leaves that look like elongated pointed scales. Vertical shoots end in spore-bearing spikelets or apical buds. On the stem of the spore-bearing spikelet sit sporophylls with sporangia on the upper side. The spores are the same, contain up to 50% non-drying oil, germinate very slowly. The gametophyte develops in the soil in symbiosis with a fungus (mycorrhiza), which, receiving carbohydrates, amino acids and phytohormones from a vascular plant, makes water and minerals, primarily phosphorus compounds, available for absorption and absorption by the plant. In addition, the fungus provides the plant with a larger absorption surface, which is especially important when it grows in poor soil. The gametophyte develops within 12-20 years, has rhizoids, has no chloroplasts. However, in some species it develops on the soil surface, then chloroplasts appear in its cells.

gametophyte bisexual, shaped like an onion, becomes saucer-shaped as it develops, bears numerous antheridia and archegonia. Mature antheridia are almost completely immersed in the gametophyte tissue or slightly protrude above its surface. The archegonium consists of a narrow abdomen immersed in the gametophyte tissue and a long or short neck protruding above its surface. Antheridia usually mature before archegonia. A zygote without a dormant period germinates and gives rise to an embryo. Vegetatively propagated by parts of the stem and rhizome. Some club mosses also have specialized organs of vegetative reproduction: brood nodules on the roots, brood bulbs or buds on the tops of the shoots.

The development cycle of the club-shaped club: A - sporophyte; B - gametophyte; 1 - creeping shoot with adventitious roots; 2 - ascending shoots; 3 - leg of spore-bearing spikelets; 4 - leaflets: ascending shoot (a) and legs of spore-bearing spikelets (b); 5 - spore-bearing spikelets; 6 - spores: view from the ventral (c) and dorsal (d) sides; 7 - sporangia; 8 - disputes; 9 - germinating spore; 10 - archegonium; 11 - antheridium; 12 - fertilization; 13 - fertilized egg; 14 - development of a new sporophyte on the gametophyte.

Horsetails (Horsetails)

The living species are exclusively herbaceous plants ranging in height from a few centimeters to several meters.

In all species of horsetail, the stems have a regular alternation of nodes and internodes.

The leaves are reduced to scales and arranged in whorls at the nodes. Lateral branches are also formed here.

The underground part of horsetails is represented by a highly developed rhizome, in the nodes of which adventitious roots are formed. In some species (horsetail), the lateral branches of the rhizome turn into tubers, which serve as a place for deposition of reserve products, as well as organs of vegetative reproduction.

Horsetail structure

Horsetails are herbaceous plants with annual above-ground shoots. A small number of species are evergreen. The size of horsetail stems varies greatly: there are dwarf plants with a stem 5–15 cm high and 0.5–1 mm in diameter, and plants with a stem several meters long (in polychaete horsetail, the stem reaches a length of 9 m). Horsetails of tropical forests reach a height of 12 m. The underground part is a rhizome, creeping, branched, in which nutrients can be deposited (tubers are formed) and which serves as an organ of vegetative reproduction. Above-ground shoots grow at the top. Summer shoots are vegetative, branched, assimilating, composed of segments, with well-developed internodes. Whorled and also dissected branches branch off from the nodes. The leaves are inconspicuous, grow together into serrated sheaths, which dress the lower part of the internode. Silica is often deposited in the epidermal cells of the stem, so horsetails are poor food.

Spring shoots are spore-bearing, non-assimilating, unbranched, spore-bearing spikelets are formed on their top. After the spores mature, the shoots die off. Spores are spherical, with four springy ribbons, greenish, germinate into growths, unisexual - male or female. There are cases when antheridia and archegonia grow on the same growth. From a fertilized egg, a pregrowth grows, and then an adult horsetail.

Horsetails often make up a significant percentage of grassland in grasslands and wetlands; widespread in acidic soil. Most often, we have field horsetail, meadow horsetail, marsh horsetail, marsh horsetail and forest horsetail.

Horsetails reproduce sexually. Sexual generation - gametophyte (growth). The gametophytes produce antheridia and archegonia. In antheridia, polyflagellated spermatozoa develop, and in archegonia, eggs. Fertilization takes place in the presence of drip-liquid water, and a sporophyte grows from the zygote without a dormant period.

Lesson number 36 (botany) Grade 6

The structure, reproduction and development of horsetails. The value of horsetail in nature and human life.

Tasks: To form knowledge about the features of the structure, reproduction and significance of horsetails. To form concepts about the complication and development of plants.

DURING THE CLASSES:

1. Poll on the previous topic (in writing):

Performing a test followed by peer review. After checking, students give a grade using the proposed grading criteria.

1. The following do not belong to ferns: A) horsetail B) club moss C) sphagnum

2. Ferns include: A) cuckoo flax B) club moss C) riccia

3. Ferns are characterized by the following features:

A) the presence of a stem, leaves and root B) the presence of a stem and leaves C) the presence of rhizoids and thallus

4. Vayami are called: A) shoots of ferns B) rhizomes of ferns C) dissected leaves of ferns

5. What develops in ferns in sporangia: A) seeds B) pollen C) spores

6. Ferns need water for: A) movement B) reproduction C) respiration

7. Under what conditions do ferns grow: A) in humid and shady places B) in dry and sunny places C) in cold and humid places

8. Mosses, club mosses, horsetails and ferns have similarities:

A) Under breeding conditions. For sexual reproduction, the presence of water is necessary. B) In the structure of the body. The body consists of roots, stems and leaves B) There are root-like formations. There are rhizoids D) In ​​the methods of reproduction. Propagated by seeds

9. A fern gametophyte is called: A) Outgrowth B) Seedling C) Zygote D) Embryo

10. The life cycle of a fern is dominated by: A) Sporophyte B) Gametophyte

Test answers:

1 - B 4 - B 7 - A 10 - A

2 - B 5 - C 8 - A

3 - A 6 - B 9 - A "5" -10 correct answers; "4" - 9-8 correct answers; "3" -7-6 correct answers.

2. Learning new material:

(slide 1,2,3 presentation)

In the modern plant world, there are a little more than 30 species of horsetails. All of them are perennial spore herbaceous plants with a thin rhizome with nodules in which nutrients are deposited. The aerial part of the stem reaches 0.5-1 m or more. A characteristic feature of horsetails is the division of the body into nodes and internodes. Horsetails have no leaves, they look like teeth, which, growing together at the base, form a sheath that covers the knot. The strongly modified lateral branches look like leaves. Photosynthesis in horsetails takes place in the stem. The stem is ribbed and impregnated with silica. There are many cavities in the stem, some of them are filled with air, others are filled with water. This structure is due to the habitats of horsetails: meadows, swamps, banks of reservoirs. . The underground stem (rhizome) is located at different depths. There are horizontal and vertical rhizomes. Horizontal rhizomes are thicker, with longer internodes than vertical ones. Tubers are formed on the rhizomes - a thickened and modified internode of the branch. Tuber cells are very large and filled with starch grains.

Reproduction and development of horsetails

(slide 4.5 presentation)

In the spring, shoots grow on the rhizomes, on the tops of which spore-bearing spikelets are located. Spikelets contain sporangia in which spores are formed. After the opening of the sporangia, the spores spill out and are carried by the wind. From spores, gametophytes (growths) develop in the form of plates with a diameter of several mm to 3 cm. On the underside of the gametophyte, colorless rhizoids up to 1 cm long appear, with the help of which it attaches to the soil and absorbs water with mineral salts dissolved in it. Horsetail reproduces vegetatively (with the help of rhizomes and nodules), asexual and sexual methods, with alternating asexual (sporophyte) and sexual (gametophyte) generations. The sporophyte predominates in the developmental life cycle. Horsetails are isosporous plants, but their gametophytes are dioecious, that is, male outgrowths with antheridia are formed from some outwardly identical spores, and female outgrowths bearing archegonia are formed from others. Spermatozoa are multiflagellated. Fertilization takes place in water. The most common are field, meadow, forest and marsh horsetails.

The value of horsetail in nature and human life

Both in nature and in human practice, the role of horsetails is insignificant. Extinct tree-like horsetails played an important role in the formation of coal throughout the world. Almost all of them are malicious hard-to-eradicate weeds. In autumn and winter they serve as food for deer and wild boars. Young vegetative shoots of horsetail are used in medicine as a diuretic.

It is believed that horsetails originated from rhinophytes. Their development went in the direction of size reduction. All horsetails, except horsetails, have become extinct. They did not give rise to other groups of plants and represent a blind branch of development.

D.z. abstract

The vegetative reproduction of the horsetail is due to the rhizome, which makes it a malicious weed, which is very difficult to get rid of. The old parts of the rhizomes die off and the initially single mother plant breaks up into several new ones.

asexual reproduction

Spore-bearing or spring shoots (Fig. 14 - 1) of horsetail, pinkish-brown, appear in early spring, unbranched. They are often eaten by the people of Asia and North America.

At their top, a spore-bearing spikelet is formed (Fig. 14 - 1 stake), on the axis of which sporophylls are located, carrying sporangia with spores. After sporulation, spring shoots die off. Spore-bearing spikelets in horsetails appear one at a time at the top of the main shoot. In most species of horsetails, the shoot that carries the spikelet is green and assimilating. But in horsetail, the spore-bearing shoot does not take part in photosynthesis.

The spikelet of horsetail consists of numerous sporophylls - sporangiophores (Fig. 14 - 2), collected by whorls of its axis. Sporophylls consist of a stem (Fig. 14 - 2n) and a shield disk located on its top (Fig. 14 - 2sh), usually having a hexagonal shape. On the side of the disk, around the stem, there are 5–13 sac-like sporangia (Fig. 14–2c), in the mature state they are covered with a single-layered wall. The sporophylls in the spikelet are tightly pushed to each other. By the time of maturation of the sporangia, the axis of the spikelet grows somewhat (the bases of all internodes have meristematic tissue) and the whorls of sporophylls move apart. In sporangia, a large number of identical spores are formed, since horsetail is an isosporous plant. The spore (Fig. 14 - 3), in addition to two shells of endo- and exosporium, is dressed in a third - outer shell - episporium. The outer shell is not continuous, but consists of two spirally twisted ribbons (springs, elater), expanding spatulately at 4 ends and attached to the spore in one place. Springs (elaters) in dry weather gradually unwind (Fig. 14 - 4), fully untwisted elaters (Fig. 14 - 5) of different spores cling to each other, which contributes to the spread of spores in groups, groups (Fig. 14 - 6). In wet weather, the elaters curl around the spore.

The sporangia open with a longitudinal fissure; after the whorls of sporophylls are separated, the spores spill out. Once on the ground, the spores germinate into a growth, which is a horsetail gametophyte.

sexual reproduction

The horsetail outgrowth has the appearance of a green, repeatedly dissected plate 0.1–0.9 cm in size. Antheridia and archegonia appear either on the same outgrowth or on different outgrowths, despite the fact that the spores are morphologically the same. Many species of horsetails have a physiological heterogeneity.

Horsetail spores, connected in groups due to adhesion by springs, when they hit the soil, find themselves in unequally favorable conditions for lighting, water supply, etc. (e.g. top and bottom spores in a pile). Germinating, some of them form smaller male growths (Fig.14 - 7) with antheridia (Fig.14 - 7an), others, larger - female growths (Fig.14 - 10) with archegonia (Fig.14 - 10a) . This phenomenon can be considered as a well-known echo of the morphological heterogeneity of horsetail ancestors, especially since in some species the physiological heterogeneity is constant and is not related to the conditions for the development of outgrowths.

And for the field horsetail, the following was experimentally established: by watering the growths on which antheridia began to develop with a nutrient solution, it is possible to increase their size and develop archegonia on them.

Horsetail antheridia (Fig. 14 - 8) are immersed in the tissue of the growth. Each of them develops more than 200 polyflagellated spermatozoa (Fig. 14 - 9). Archegoniums (Fig. 14 - 11), only with a neck rise above the growth. Fertilization is carried out in wet weather. A fertilized egg gives rise to an embryo (Fig. 14 - 12). A horsetail suspension is not formed. The embryo is initially hidden in the tissue of the growth. It consists of a stem (Fig. 14 - 12h), a rudimentary root (Fig. 14 - 12k), 2-3 first leaves (Fig. 14 - 12pl) and a stalk in the form of a growth point (Fig. 14 - 12p). Punching the tissue of the growth, the root is strengthened in the ground, and the plant passes to an independent life. Several embryos often appear on one outgrowth.

Horsetail as a medicinal plant was known even in ancient times. An infusion of herbs is used as a diuretic for edema due to circulatory failure, as well as for inflammatory diseases of the bladder and urinary tract, for pleurisy, tuberculosis, for dysentery, and as a hemostatic agent for dysentery. Internal use of horsetail, as a poisonous plant, requires caution, that is, it is necessary to strictly observe the dosage.