Who has plants with a shortened stem? Short stems
Like the foundation of nature
I honor the strength of the butt in the tree -
He makes transitions
Crowns to roots, light to darkness
Yu. Linnik “Earth”
Goal: learning new material
Lesson form: combined
Lesson objective: to study the structure of the stem in connection with its functions
Equipment: table “Structure of the stem”, slides “Types of stems”, a selection of riddles and poems about the stem, slides with experiments.
During the classes
- Organizing time
- Testing students' knowledge
- Learning new material
1) There is a riddle about the structure of the plant:
One is digging in the ground,
The other is bathed in light;
And although they are friends,
They cannot be exchanged.
2) What friends are we talking about in this riddle? (Roots and leaves)
3) What organ of the plant helps them to be friends, maintains their relationship? (Stem)
4) How is this relationship accomplished?
- Demonstration of experiments:
- A branch of lilac and balsam in water tinted with ink.
- A ringed (dry) branch with a formed influx.
5) What do the experiments presented here prove?
So, the stem is a plant organ through which water and mineral substances dissolved in it move (ascend) from the root, and organic substances formed in the leaves descend. The stem supports the leaves and carries them towards the light.
6) Which plants are the world champions in height?
Students look at slides of sequoia and eucalyptus.
7) What plants are the tallest in our forests?
(Trees: spruce, pine, poplar; herbs: kupir, reed).
8) Sequoia and eucalyptus have the tallest stems in the world, but not the longest. Which plants have the longest stems?
(Rattan palms are tropical vines with large feathery leaves and a stem covered with thorns, 300-400 m long). Students look at the slide.
9) The height or length of the stem is the result of its growth. How does the stem grow? In order to find out, first apply ink to the stem of the pea sprout every millimeter. Where will they spread the most? We observe that this occurs at the upper end of the seedling. This means that the stems grow from their top. (Students look at the slides) However, not everyone:
There are stems with cunning - they grow from the middle. (Cereals, Umbelliferae)
In cereals, every internode grows. Thanks to this growth (intercalary), the stem of the world's largest cereal, bamboo, under favorable conditions, lengthens by 42.5 cm per day. If a tired traveler hangs his hat on the bamboo and falls asleep, then when he wakes up in the morning, he will hardly be able to get it out.
Along with plants that have tall and long stems, there are those that have shortened stems.
10) Which representatives of our flora have a shortened stem?
(The shortened stem of dandelion and plantain. This is a kind of protection against trampling.)
On the road, where foot and horse
Day and night it prints a trace,
The plantain has broken through green
From under an old stone into the light.
It grows, drowning in the road
Compacted stuffy dust,
Unruly, robust plantain
Not easy to get off the ground.
(V. Stepanov)
Plants are extremely diverse in the thickness of their stems (trunks).
11) Which plants have the thickest stem?
Either believe it or not,
Word went around the whole world,
What's on the stump to the sound of guitars
Twenty couples danced!
The trunk of a giant sequoia can reach 48 m in girth. Newspapers reported that a piano, four musicians and 16 dancing couples were placed on the stump of one such plant (slide). Due to their height, these trees do not seem so thick.
Another tree is the baobab - an inhabitant of tropical savannas (slide). Its trunk has a diameter of 4-10 m and a height of up to 20 m and is usually hollow. Inside such a trunk 20-30 people could easily sleep overnight.
12) How can you determine the age of a felled tree?
Ignashka is growing in breadth,
Whatever the year - a shirt,
The old one will not be replaced,
He'll put on a new one.
How old is Ignashka?
Count the shirts!
(“Shirt” - annual layers of wood.)
How many rings are on a stump, how old is the tree; It is no coincidence that they say that the passport of a tree is hidden in a stump. Plant stems can have the most unusual shapes. In prickly pears they are flat, like cakes, in echinocactus they are completely round (Slide).
The bottle tree has a stem shaped like a bottle.
Plant stems carry their leaves to the light in different ways. Sequoia and poplar have erect stems. The stems of some plants do not rise up without support from other plants. For this they have special devices. They are often called acrobats for this. If the plant does not find support, it spreads along the ground.
13) What acrobat plants do you know?
(Acrobat plants include: hops, bindweed).
The whole field is confused,
In it both up and down
It curls and creeps lazily
Pale pink bindweed.
(N. Kholodkovsky)
14) What adaptations do acrobat plants have to climb up?
(The stems of some plants of the legume family cling with the help of modified leaf blades - tendrils.)
Mustachioed man
Caught on a twig -
Hanging on his mustache,
Doesn't fall down.
(Stems of hops and decorative beans curl around the support. Ivy creeps along the wall with the help of adventitious roots).
Up the steep wall
On cast concrete,
The centipede crawls
He takes the leaves with him.
Plants with climbing and climbing stems are also called vines. Unusually diverse and powerful vines grow in the wilds of tropical rainforests; they are also called strangler plants.
Liana upholsters a tree,
It clings slyly to its trunk,
And the tree almost believed
The sincerity of her concerns.
In the dense jungle
spicy humidity,
And the screams of impudent monkeys,
And the stuffiness is so drunk,
That every stem is drunk with it.And here comes the creeping liar
Villainy celebrates:
The forest giant is twisted like a chain
Her insidious tenderness.
She lives on other people's juices,
She looks so weak.
And the crown of a tall tree
No one will come back to life.
(O. Vysotskaya)
15) What plants with creeping stems do you know?
Under the tight-fisted foot
The stem lay springy,
And the leg will pass -
The stalk stands up.
(Bird buckwheat)
Shoots can have unusual and interesting modifications. You look at such formations and you won’t immediately understand that this is an escape.
16) What modifications are mentioned in the riddles?
At the bald head
There are eyes and eyebrows,
The eyes are slightly slanted,
And the eyebrows are hairless.
(potato tuber)
Ten barrels tight
Inserted into each other
And only the bottom
They have one.
(Onion, bottom - shortened stem)
There is a rope in the ground,
And there is a storage room in it.
(Rhizome of wheatgrass, lily of the valley)
17) How to distinguish a rhizome from a root?
(Show leaf scars on the lily of the valley rhizome)
Hidden from the sun
Closed in the ground:
There is a trace of scales on it...
Either the root or not?!
18) What is the significance of shoot modifications such as tubers and rhizomes for a plant?
With the help of tubers and rhizomes, plants reproduce vegetatively, and nutrients are stored in them. Plants can store not only organic matter in their stems, but also water.
19) What plants have the ability to store water in their stems, and what does this mean for them?
By storing large amounts of water in their stems, cacti can withstand prolonged drought and grow in desert conditions. The following fact is known: a huge echinocactus weighing 37 kg was in the room for six years, being torn from the soil. During this time, he “lost weight” by 11 kg and still did not die.
20) What is the name of this thorny plant, and where are its stems and leaves?
(Demonstration of a houseplant - butcher's broom)
There's a masquerade on the window -
Everything changes its outfit:
The stem is dressed with a leaf,
And the leaf became a thorn.
With the help of various modifications of the stem, vegetative propagation of plants occurs. Potatoes reproduce by tubers. And the malicious wheatgrass weed - with the help of rhizomes, this is the difficulty of fighting it.
21) How does the plant propagate, about which they say:
Does mom have a daughter on a string? (Strawberries, houseplant saxifrage - with the help of creeping shoots - tendrils)
Vegetative propagation can also be carried out by sections of above-ground shoots (cuttings)
And the twig will not give up its roots,
When it ends up underground.
22) Which plants of our flora are easily propagated by cuttings?
(willow, poplar, currant)
23) What is the significance of plant stems for humans?
The stems of woody plants provide valuable building material, wood, and the most important raw material for the chemical industry. The wood of different types of trees differs in color, pattern, hardness and density. Hard and heavy wood is found in boxwood, pear, the so-called ironwood, which sinks in water, and the tropical backout tree. The lightest wood, somewhat reminiscent of foam, is balsa wood. It was from this that the Kon-Tiki raft of the famous traveler Thor Heyerdahl was made.
The bark of the cork tree is used to make life belts, rings, and is valued as an insulating material. All kinds of utensils are made from thick bamboo stems, and canes, sticks, and fishing rods (slides) from its thin stems.
Different tree species amaze us with the richness of colors and patterns (textures) of their wood. A clear example of this is the wonderful collections of parquet floors of Russian palaces (slides about the parquet floors of the Peterhof and Ostankino palaces)
24) Where is wood used?
Man has long used wood in the construction of homes, cathedrals, and temples. A masterpiece of Russian wooden architecture is the twenty-two-domed Church of the Transfiguration in Kizhi on Lake Onega. You look at this creation of the hands of mankind and you are amazed. Each dome of the church is covered with many different aspen planks, called ploughshares (slides from the “Wooden Tale” set)
On the treasured island,
On a high place
built this church
Master Nestor.
Twenty-two-headed
He delivered a miracle
And to see it is given
To everyone and everywhere.When is the last dome
The master took it to the sky,
He threw his ax
To stormy Onega.
And they took off like swifts
Fiery dawns.
That's all -
Kizhi stands
On the Onega Sea. (A. Prokofiev)
In addition to the construction of buildings and structures, wood is used in the production of furniture, sleepers for railways, in the manufacture of telegraph poles, etc. Wood is also an important raw material for the chemical industry.
25) What products does wood produce during chemical processing?
You can use a table or slide based on the book by N.M. Verzilin “Plants in Human Life” (1952)
Born in a dark forest,
Spread a white canvas.
(Paper)Not in a field, but in a forest
Shirts have grown.
(Artificial silk from wood)
26) The stems of which plants provide us with valuable natural fiber?
Blue-eyed boy
He saved us shirts.
Was - a reed
Became a sheet.
(Linen)
Where did the bast come from?
Is it starting?
(Linden bast)
27) The use of wood in industry and everyday life leads to the death of trees. How can you use their trunks without cutting down trees?
A short run
Half-heartedly
An ax cuts an arrow
And sticky blood of wood
Flows into the pot along the trunk.
Calm as donors, pine trees,
And keeping your turn,Breadwinners are like nurses
They make their rounds silently.
Zhivitsa is an amber word!
I'm walking through the forest, and she
Honey oozes down the cuts,
Spring on the plots, spring!
(V. Sokolov “Zhivitsa”)
Resin obtained by cutting trees (pine, spruce) contains essential oil (turpentine) and solid resin (rosin). They are widely used in the production of varnishes, plastics, and the medical industry.
28) The stems of what other plants known to you are used to collect resin?
A bush grew in a tub -
And wide and thick:
Leaf like leather
Tightly folded
The trunk is elderberry,
The juice is rubbery.
(Ficus)
Natural rubber, extracted mainly from Hevea, despite the widespread use of synthetic rubber, has not lost its importance today and is produced in tropical countries.
Juices and resins flowing from wounded tree trunks are used by humans not only for technical purposes, but also for food.
29) What trees are cut for this purpose?
A birch tree can secrete more than 100 liters of sap during the cutting period (horses in April, early May) without much harm to itself.
They call it tears -
In vain! Tears are salty.
White birch, live, -
The joy of this side.
And as soon as spring comes,
The guys are running to the rings
For sweet juice
What's popular
Our name is birch tree.
And they drink still juice, getting drunk,
They become bolder, stronger,
Still unable to open up
In love for my native land
(A. Baeva)
Sugar maple sap is widely used in America. Sap containing 5-6% sugar flows from the wounded trunk of a tropical sugar palm. From each cut 5-7 liters of sap flows out per day. Residents of the tropics make a national drink from it - toddy.
In tropical countries there are plants that are jokingly called a tree - a cow. When it is cut, a liquid flows out, reminiscent of cow's milk in its taste, appearance and nutritional properties.
30) The stems of which plants are used by humans for food?
Green branches and fruits -
Neither livestock nor people;
There is no food in the root either,
What are we going to eat?!
(Potato tubers)In the garden, behind the barn,
The stem has grown into a ball.
The stem is a capsule,
To taste - stump.
(Kohlrabi)
Columns of beautiful white-trunked birches in the forest evoke delight and admiration in us. The pine forest gives us beauty and joy. The trunks of these trees with copper scaly bark, with drops of amber resin, exude an amazing aroma full of healing power (Slides: birch grove, pine forest)
There is an abundance of music in the trees,
Songliness in silent lines.
We are neither fake nor hackneyed
We won't hear any melodies in them.
It's not the beeches who cross their arms,
It is not elms that bind blood, -
Then sounds hang above the ground
Bends of branches and trunks.
(L. Vysheslavsky “Branches”)
Reinforcing the material covered.
External structure of the stem. The stem is axial part escape. The stem is made up of nodes and internodes. Depending on the degree of elongation of the internodes, the stem can be elongated or shortened. Yes, y sunflower, corn, asters, gladiolus stem elongated. And plantain, dandelion, daisy, primrose, echeveria, saintpaulia the stem is shortened.
The cross section shows that the stem most often has a rounded shape. But it can also be triangular (at sedges), and tetrahedral (at nettle) or have a different shape.
Internal structure of the stem. Let's look at the internal structure of the stem in a cross section. Outside, the stem is protected by integumentary tissues. In young stems in spring, the cells of the integumentary tissue are covered with thin peel . In perennial plants, by the end of the first year of life, the skin is replaced by a multilayered one. cork consisting of dead cells filled with air. For breathing, there are stomata in the skin (of young shoots), and later they are formed lentils - large, loosely arranged cells with large intercellular spaces.
Adjacent to the covering tissue bark formed by different tissues. The outer part of the cortex is represented by layers of mechanical tissue cells with thickened membranes and thin-walled cells of the main tissue. The inner part of the cortex is formed by cells of conducting tissue and is called bast .
The composition of the bast includes sieve tubes , along which there is a downward current: organic substances move from the leaves. Sieve tubes consist of cells connected at their ends into a long tube. There are small openings between adjacent cells. Organic substances formed in the leaves move through them, like through a sieve.
Sieve tubes do not remain alive for long, usually 2-3 years, occasionally - 10-15 years. New ones are constantly being formed to replace them. Sieve tubes form a small part in the phloem and are usually collected in bundles. In addition to these bundles, the phloem contains cells of mechanical tissue, mainly in the form bast fibers , and cells of the main tissue.
To the center of the bast in the stem there is another conductive tissue - wood .
Wood is formed by cells of different shapes and sizes and consists of vessels (trachea), tracheid And wood fibers . An upward current flows through them: water with substances dissolved in it moves from the roots to the leaves.
In the center of the stem lies a thick layer of loose cells of the main tissue, in which reserves of nutrients are deposited - this core .
In some plants (dahlia, tulip, cucumber, bamboo ) the core is occupied by an air cavity.
Between the wood and the bast of dicotyledonous plants there is a thin layer of educational tissue cells - cambium . As a result of the division of cambium cells, the thickness of the stem increases (grows). Cambium cells divide along their axis. One of the daughter cells that appears goes to the wood, and the other to the phloem. The increase is especially noticeable in wood. The division of cambium cells depends on the seasonal rhythm - in spring and summer it is active (large cells are formed), in autumn it slows down (small cells are formed), and in winter it stops. As a result, an annual increase in wood is formed, clearly visible in many trees, called tree ring . By the number of growth rings, you can calculate the age of the shoot and the tree as a whole.
The width of growth rings in woody plants depends on environmental conditions. Thus, in cold climates, on marshy soils, the size of the annual rings of wood is very small. In favorable climatic conditions, on rich soils, the thickness of tree rings increases. By comparing the alternation of wide and narrow growth rings near the trunk, it is possible to determine the conditions in which the plant lived, as well as to establish fluctuations in weather conditions over many years.
Functions of the stem. In plant life, the stem performs different functions. It conducts water with solutions of mineral salts from the root to the leaves and removes the organic substances formed in them. Conductive - the main function of the stem.
The stem serves as a support for the plant; it bears the weight of the leaves, flowers and fruits on it. Support - another important function of the stem.
Spare nutrients may be deposited in the stem. This shows storing function of the stem.
With the help of the stem, the shoot brings its leaves and buds to the light as the plant grows. This reveals an important axial stem function and growth function.
The stem performs all these functions through conductive, mechanical and storage educational tissues.
Interactive lesson-simulator. (Complete all lesson tasks)
The stem is an important part of the shoot. It performs various functions: axial, conducting, supporting, storing. The external and internal structure of the stem is determined by the functions that the stem performs in the life of the plant. An upward current flows through the wood of the stem, and a downward current flows through the phloem. Through the division of cambium cells, the stem grows in thickness. By looking at the growth rings, you can determine the age of the plant and the conditions in which it grew.
Theory for preparation for block No. 4 of the Unified State Exam in biology: with system and diversity of the organic world.
Root
Root- an underground vegetative organ of higher plants with unlimited growth in length.
Root functions
- Fixing the plant in the substrate
- Absorption, conduction of water and minerals
- Nutrient supply
- Interaction with the roots of other plants, fungi, microorganisms living in the soil (mycorrhiza, legume nodules)
- Vegetative propagation
- Synthesis of biologically active substances
- In many plants, the roots perform special functions (aerial roots, sucker roots)
- Modifications and specialization of roots
- The roots of some buildings have a tendency to metamorphose
The roots are different, namely, they can change.
Root modifications
- Root vegetable - a modified succulent root. The main root and the lower part of the stem are involved in the formation of the root crop. Most root plants are biennial. Root vegetables consist mainly of storage tissue (turnips, carrots, parsley).
- Root tubers - root tubers (root cones) are formed as a result of thickening of lateral and adventitious roots (tulips, dahlias, potatoes).
- Aerial roots are lateral roots that grow downwards. Absorb rainwater and oxygen from the air. Formed in many tropical plants under conditions of high humidity.
- Mycorrhiza is the cohabitation of the roots of higher plants with fungal hyphae. With such mutually beneficial cohabitation, called symbiosis, the plant receives water with nutrients dissolved in it from the fungus, and the fungus receives organic substances. Mycorrhiza is characteristic of the roots of many higher plants, especially woody ones. Fungal hyphae, entwining the thick lignified roots of trees and shrubs, perform the functions of root hairs.
- Bacterial nodules on the roots of higher plants - the cohabitation of higher plants with nitrogen-fixing bacteria - are modified lateral roots adapted to symbiosis with bacteria. Bacteria penetrate through the root hairs into young roots and cause them to form nodules.
- Respiratory roots - in tropical plants - perform the function of additional respiration.
There are:
- main root
- lateral roots
- adventitious roots
The main root develops from the embryonic root. Lateral roots occur on any root as a side branch. Adventitious roots are formed by the shoot and its parts.
The collection of roots of one plant is called the root system.
Types of root systems
- Rod
- fibrous
- Branched
IN core In the root system, the main root is highly developed and clearly visible among other roots (characteristic of dicotyledons). The tap root system usually penetrates deeper into the soil than the fibrous root system.
IN fibrous In the root system, in the early stages of development, the main root, formed by the embryonic root, dies, and the root system is composed of adventitious roots (typical of monocots). The fibrous root system better entwines adjacent soil particles, especially in its upper fertile layer.
IN branchy The root system is dominated by equally developed main and several lateral roots (in tree species, strawberries).
The escape
The escape- This is a stem with leaves and buds located on it.
The components of the shoot are the stem, leaves, and buds. When a seed germinates from the embryonic bud, the first shoot of the plant is formed - its main shoot, or shoot of the first order. From the main shoot, side shoots, or shoots of the second order, are formed, and when branching is repeated - of the third order, etc. Additional shoots are formed from adventitious buds.
This is how a system of shoots is formed, represented by the main shoot and lateral shoots of the second and subsequent orders. The shoot system increases the total area of contact of the plant with the air.
The shoot on which flowers are formed is called a flowering shoot, or peduncle (sometimes the term “peduncle” is understood in a narrower sense - as the section of the stem on which the flowers are located).
A vegetative unmodified shoot is a single plant organ, consisting of a stem, leaves and buds, formed from a common array of meristem (shoot growth cone) and possessing a single conducting system. Stems and leaves, which are the main structural elements of the shoot, are often considered as its constituent organs, that is, second-order organs. In addition, a mandatory accessory to the shoot is the buds. The main external feature that distinguishes a shoot from a root is the presence of leaves.
In the seasonal climate of temperate latitudes, the growth and development of shoots from the buds is periodic. In shrubs and trees, as well as in most perennial grasses, this happens once a year - in spring or early summer, after which the wintering buds of the next year are formed, and at the end of summer - in the fall, shoot growth ends.
Escape structure
A (with leaves). 1 - stem; 2 – sheet; 3 – node; 4 - internode; 5 – leaf axil; 6 – axillary bud; 7 – apical bud.
B (after leaf fall). 1 – apical bud; 2 – kidney rings; 3 – leaf scars; 4 - lateral buds.
Types of shoots
1 – erect; 2 – rising; 3 – creeping; 4 – creeping; 5 – curly; 6 – climbing.
Modifications of shoots
- The thorn is a highly lignified, leafless, shortened shoot with a sharp tip. The spines of shoot origin perform mainly a protective function. In wild apple, wild pear, and laxative buckthorn (Rhamnus cathartica), shortened shoots that have limited growth and end in a point turn into thorns.
- A tendril is a rope-like branched or unbranched shoot of a metameric structure, typically devoid of leaves. Stem tendrils, as a highly specialized shoot, perform a supporting function.
- Rhizome is an underground shoot with scale-like leaves of the lower formation, buds and adventitious roots. Thick, highly branched creeping rhizomes are characteristic of wheatgrass, short and rather fleshy - for kupena, iris, very thick - for egg capsule, water lily.
- A stem tuber is a modified shoot with a pronounced storage function of the stem, the presence of scale-like leaves that quickly peel off, and buds that form in the axils of the leaves and are called eyes (jerusalem artichoke).
- A bulb is an underground (less often above-ground) highly shortened specialized shoot, in which reserve substances are deposited in leaf scales, and the stem is transformed into a bottom. The bulb is a typical organ of vegetative renewal and reproduction. Bulbs are characteristic of monocotyledonous plants from the family Liliaceae (lily, tulip, onion), Amaryllidaceae (amaryllis, narcissus, hyacinth), etc. As an exception, they are also found in dicotyledons - in some species of sorrel and butterwort.
- A corm is a modified underground shortened shoot with a thick stem that stores assimilates, adventitious roots growing from the underside of the corm, and preserved dried leaf bases (membranous scales), which together constitute a protective cover. Corms include colchicum, gladiolus, ixia, and saffron.
Stem
Stem- an elongated shoot of higher plants, serving as a mechanical axis, also serves as a producing and supporting base for leaves, buds, and flowers.
Classification of stems
By location relative to soil level:
above ground
underground
According to the degree of lignification:
- herbaceous
- woody (for example, a trunk is the main perennial stem of a tree; the stems of shrubs are called stems)
By direction and nature of growth:
- erect (for example, sunflower)
- recumbent (creeping) - stems lie on the surface of the soil without rooting (monetary loosestrife)
- ascending (ascending) - the lower part of the stem lies on the surface of the soil, and the upper rises vertically (cinquefoil)
- creeping - stems spread along the ground and take root due to the formation of adventitious roots at the nodes (ivy budra)
- clinging (climbing) - attached to a support using antennae (peas)
- climbing - thin stems wrapping around a support (lunasperium)
According to cross-sectional shape:
- rounded
- flattened
- three-, four-, polyhedral (faceted)
- ribbed
- grooved (grooved)
- winged - stems in which flat herbaceous outgrowths stretch along sharp edges (forest phylum) or leaf bases descending onto the stem (comfrey)
Stem structure
Outside, the stem is protected by integumentary tissues. In young stems in spring, the cells of the integumentary tissue are covered with a thin skin. In perennial plants, by the end of the first year of life, the skin is replaced by a multilayer plug consisting of dead cells filled with air. For respiration, the skin (of young shoots) has stomata, and later lentils are formed - large, loosely located cells with large intercellular spaces.
Adjacent to the integumentary tissue is a cortex formed by different tissues. The outer part of the cortex is represented by layers of mechanical tissue cells with thickened membranes and thin-walled cells of the main tissue. The inner part of the cortex is formed by cells of conducting tissue and is called the bast.
The bast consists of sieve tubes through which a downward current flows: organic substances move from the leaves. Sieve tubes consist of cells connected at their ends into a long tube. There are small openings between adjacent cells. Organic substances formed in the leaves move through them, like through a sieve.
Sieve tubes do not remain alive for long, usually 2-3 years, occasionally - 10-15 years. New ones are constantly being formed to replace them. Sieve tubes form a small part in the phloem and are usually collected in bundles. In addition to these bundles, the bast contains cells of mechanical tissue, mainly in the form of bast fibers, and cells of the main tissue.
To the center of the bast in the stem there is another conductive tissue - wood.
Wood is formed by cells of different shapes and sizes and consists of vessels (tracheas), tracheae and wood fibers. An upward current flows through them: water with substances dissolved in it moves from the roots to the leaves.
In the center of the stem lies a thick layer of loose cells of the main tissue, in which reserves of nutrients are deposited - this is the pith.
In some plants (dahlia, tulip, cucumber, bamboo), the core is occupied by an air cavity.
Between the wood and the bast of dicotyledonous plants there is a thin layer of educational tissue cells - the cambium. As a result of the division of cambium cells, the thickness of the stem increases (grows). Cambium cells divide along their axis. One of the daughter cells that appears goes to the wood, and the other goes to the bast. The increase is especially noticeable in wood. The division of cambium cells depends on the seasonal rhythm - in spring and summer it is active (large cells are formed), in autumn it slows down (small cells are formed), and in winter it stops. As a result, an annual growth of wood is formed, clearly visible in many trees, called an annual ring. By the number of growth rings, you can calculate the age of the shoot and the tree as a whole.
The width of growth rings in woody plants depends on environmental conditions. Thus, in cold climates, on marshy soils, the size of the annual rings of wood is very small. In favorable climatic conditions, on rich soils, the thickness of tree rings increases. By comparing the alternation of wide and narrow growth rings near the trunk, it is possible to determine the conditions in which the plant lived, as well as to establish fluctuations in weather conditions over many years.
Functions of the stem
- conductive (main function)
The stem serves as a support for the plant; it bears the weight of the leaves, flowers and fruits on it.
- supporting
Spare nutrients may be deposited in the stem. This shows the storage function of the stem. With the help of the stem, the shoot brings its leaves and buds to the light during the growth of the plant. This reveals the important axial function of the stem and the growth function.
Sheet
Sheet- one of the most important organs of plants, the main functions of which are photosynthesis, gas exchange and transpiration.
Internal structure of the leaf
The sheet consists of the following fabrics:
- The epidermis is a layer of cells that protect against the harmful effects of the environment and excessive evaporation of water. Often, on top of the epidermis, the leaf is covered with a protective layer of waxy origin (cuticle).
- Parenchyma is an internal chlorophyll-bearing tissue that performs the main function of photosynthesis.
- A network of veins formed by conducting bundles consisting of vessels and sieve tubes for the movement of water, dissolved salts, sugars and mechanical elements.
- Stomata are special complexes of cells located mainly on the lower surface of leaves; Through them, water evaporation and gas exchange occur.
External leaf structure
The leaf externally consists of:
- petiole (leaf stalk)
- leaf blade (blade)
- stipules (paired appendages located on both sides of the base of the petiole)
- the place where the petiole joins the stem is called the leaf sheath
- the angle formed by the leaf (leaf petiole) and the overlying internode of the stem is called the leaf axil
- in the leaf axil a bud (which in this case is called an axillary bud), a flower (called an axillary flower), an inflorescence (called an axillary inflorescence) can form.
Not all plants have all parts of leaves; in some species, paired stipules are not clearly expressed or are absent; the petiole may be missing, and the leaf structure may not be lamellar.
The organism of a flowering plant is a system of roots and shoots. The main function of above-ground shoots is to create organic substances from carbon dioxide and water using solar energy. This process is called air feeding of plants.
A shoot is a complex organ consisting of a stem, leaves, and buds formed during one summer.
Main escape- a shoot developed from the bud of a seed embryo.
Side shoot- a shoot that appears from a lateral axillary bud, due to which the stem branches.
Extended escape- shoot, with elongated internodes.
Shortened escape- shoot, with shortened internodes.
Vegetative shoot- a shoot bearing leaves and buds.
Generative escape- a shoot bearing reproductive organs - flowers, then fruits and seeds.
Branching and tillering of shoots
Branching- this is the formation of lateral shoots from axillary buds. A highly branched system of shoots is obtained when lateral shoots grow on one (“mother”) shoot, and on them, the next lateral shoots, and so on. In this way, as much air supply as possible is captured. The branched crown of the tree creates a huge leaf surface.
Tillering- this is branching in which large lateral shoots grow from the lowest buds located near the surface of the earth or even underground. As a result of tillering, a bush is formed. Very dense perennial bushes are called turfs.
Types of shoot branching
During evolution, branching appeared in thallus (lower) plants; in these plants the growing points simply bifurcate. This branching is called dichotomous, it is characteristic of pre-shoot forms - algae, lichens, liverworts and anthocerotic mosses, as well as thickets of horsetails and ferns.
With the appearance of developed shoots and buds, monopodial branching in which one apical bud retains its dominant position throughout the life of the plant. Such shoots are orderly and the crowns are slender (cypress, spruce). But if the apical bud is damaged, this type of branching is not restored, and the tree loses its typical appearance (habitus).
The most recent type of branching in terms of time of occurrence is sympodial, in which any nearby bud can develop into a shoot and replace the previous one. Trees and shrubs with this type of branching can easily be pruned, crown formed, and after a few years they grow new shoots without losing their habit (linden, apple, poplar).
A type of sympodial branching false dichotomous, which is characteristic of shoots with opposite arrangement of leaves and buds, so instead of the previous shoot, two grow at once (lilac, maple, chebushnik).
Kidney structure
Bud- a rudimentary, not yet developed shoot, at the top of which there is a growth cone.
Vegetative (leaf bud)- a bud consisting of a shortened stem with rudimentary leaves and a growth cone.
Generative (flower) bud- a bud represented by a shortened stem with the rudiments of a flower or inflorescence. A flower bud containing 1 flower is called a bud.
Apical bud- a bud located at the top of the stem, covered with young leaf buds overlapping each other. Due to the apical bud, the shoot grows in length. It has an inhibitory effect on the axillary buds; removing it leads to the activity of dormant buds. Inhibitory reactions are disrupted and the buds bloom.
At the top of the embryonic stem there is the growth part of the shoot - growth cone. This is the apical part of the stem or root, consisting of educational tissue, the cells of which constantly divide through mitosis and give the organ an increase in length. At the top of the stem, the growth cone is protected by bud scale-like leaves; it contains all the elements of the shoot - stem, leaves, buds, inflorescences, flowers. The root growth cone is protected by a root cap.
Lateral axillary bud- a bud that appears in the axil of a leaf, from which a lateral branching shoot is formed. The axillary buds have the same structure as the apical one. The lateral branches, therefore, also grow at their apices, and on each lateral branch the terminal bud is also apical.
At the top of the shoot there is usually an apical bud, and in the axils of the leaves there are axillary buds.
In addition to apical and axillary buds, plants often form so-called accessory buds. These buds do not have a certain regularity in location and arise from internal tissues. The source of their formation can be the pericycle, cambium, parenchyma of the medullary rays. Adventitious buds can form on stems, leaves, and even roots. However, in structure, these buds are no different from ordinary apical and axillary ones. They provide intensive vegetative regeneration and reproduction and are of great biological importance. In particular, root shoot plants reproduce with the help of adventitious buds.
Dormant buds. Not all buds realize their ability to grow into a long or short annual shoot. Some buds do not develop into shoots for many years. At the same time, they remain alive, capable, under certain conditions, of developing into leafy or flowering shoots.
They seem to be sleeping, which is why they are called sleeping buds. When the main trunk slows down its growth or is cut down, the dormant buds begin to grow, and leafy shoots grow from them. Thus, dormant buds are a very important reserve for the regrowth of shoots. And even without external damage, old trees can “rejuvenate” due to them.
Dormant buds, very characteristic of deciduous trees, shrubs and a number of perennial herbs. These buds do not develop into normal shoots for many years; they often remain dormant throughout the life of the plant. Typically, dormant buds grow annually, exactly as much as the stem thickens, which is why they are not buried by growing tissues. The stimulus for awakening dormant buds is usually the death of the trunk. When cutting down a birch, for example, stump growth is formed from such dormant buds. Dormant buds play a special role in the life of shrubs. The shrub differs from a tree in its multi-stemmed nature. Typically, in shrubs the main mother stem does not function for long, several years. When the growth of the main stem subsides, dormant buds awaken and daughter stems are formed from them, which outstrip the mother in growth. Thus, the shrub form itself arises as a result of the activity of dormant buds.
Mixed kidney- a bud consisting of a shortened stem, rudimentary leaves and flowers.
Kidney renewal- an overwintering bud of a perennial plant from which a shoot develops.
Vegetative propagation of plants
| Way | Drawing | Description | Example |
Creeping shoots |  | Creeping shoots or tendrils, in the nodes of which small plants with leaves and roots develop | Clover, cranberry, chlorophytum |
Rhizome |  | With the help of horizontal rhizomes, plants quickly cover a large area, sometimes several square meters. The older parts of the rhizomes gradually die and are destroyed, and individual branches separate and become independent. | Lingonberries, blueberries, wheatgrass, lily of the valley |
Tubers |  | When there are not enough tubers, you can propagate by parts of the tuber, bud eyes, sprouts and tops of tubers. | Jerusalem artichoke, potatoes |
Bulbs |  | From the lateral buds on the mother bulb, daughter buds are formed, which are easily separated. Each daughter bulb can produce a new plant. | Bow, tulip |
Leaf cuttings |  | The leaves are planted in wet sand, and adventitious buds and adventitious roots develop on them | Violet, sansevieria |
By layering |  | In spring, bend the young shoot so that its middle part touches the ground and the top is directed upward. On the lower part of the shoot under the bud, you need to cut the bark, pin the shoot to the soil at the cut site and cover it with damp soil. By autumn, adventitious roots are formed. | Currants, gooseberries, viburnum, apple trees |
Shoot cuttings | A cut branch with 3-4 leaves is placed in water, or planted in wet sand and covered to create favorable conditions. Adventitious roots form on the lower part of the cutting. | Tradescantia, willow, poplar, currant |
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Root cuttings |  | A root cutting is a piece of root 15-20 cm long. If you cut off a piece of dandelion root with a shovel, adventitious buds will form on it in the summer, from which new plants will form | Raspberry, rosehip, dandelion |
Root suckers |  | Some plants are able to form buds on their roots | |
Grafting with cuttings |  | First, annual seedlings called wildflowers are grown from seeds. They serve as a rootstock. Cuttings are taken from a cultivated plant - this is a scion. Then the stem parts of the scion and rootstock are connected, trying to connect their cambium. This way the tissues grow together more easily. | Fruit trees and shrubs |
Kidney grafting |  | An annual shoot is cut from a fruit tree. Remove the leaves, leaving the petiole. Using a knife, an incision is made in the bark in the shape of the letter T. A developed bud from a cultivated plant, 2-3 cm long, is inserted. The grafting site is tightly tied. | Fruit trees and shrubs |
Tissue culture |  | Growing a plant from educational tissue cells placed in a special nutrient medium. | Orchid, carnation, gerbera, ginseng, potato |
Modifications of underground shoots
Rhizome- an underground shoot that performs the functions of deposition of reserve substances, renewal, and sometimes vegetative propagation. The rhizome has no leaves, but has a well-defined metameric structure; nodes are distinguished either by leaf scars and remains of dry leaves, or by leaf scars and remains of dry leaves, or by living scale-like leaves and the location of axillary buds. Adventitious roots can form on the rhizome. From the buds of the rhizome, its lateral branches and above-ground shoots grow.
Rhizomes are characteristic mainly of herbaceous perennials - hoofweed, violet, lily of the valley, wheatgrass, strawberry, etc., but are also found in shrubs and shrubs. The lifespan of rhizomes ranges from two or three to several decades.
Tubers- thickened fleshy parts of the stem, consisting of one or more internodes. There are above-ground and underground.
Overhead- thickening of the main stem and side shoots. Often have leaves. Aboveground tubers are a reservoir of reserve nutrients and serve for vegetative propagation; they may contain metamorphosed axillary buds with leaf buds, which fall off and also serve for vegetative propagation.
Underground tubers - thickening of the subcotyledon or underground shoots. On underground tubers, the leaves are reduced to scales that fall off. In the axils of the leaves there are buds - eyes. Underground tubers usually develop on stolons - daughter shoots - from buds located at the base of the main shoot, look like very thin white stems bearing small colorless scale-like leaves, grow horizontally. Tubers develop from the apical buds of stolons.
Bulb- an underground, less often above-ground shoot with a very short thickened stem (bottom) and scaly, fleshy, succulent leaves that store water and nutrients, mainly sugar. Aboveground shoots grow from the apical and axillary buds of the bulbs, and adventitious roots form on the bottom. Depending on the placement of leaves, bulbs are classified as scaly (onion), imbricated (lily) and compound or complex (garlic). In the axil of some scales of the bulb there are buds from which daughter bulbs develop - children. Bulbs help the plant survive in unfavorable conditions and are an organ of vegetative propagation.
Corms— outwardly similar to bulbs, but their leaves do not serve as storage organs, they are dry, filmy, often the remains of sheaths of dead green leaves. The storage organ is the stem part of the corm; it is thickened.
Aboveground stolons (lashes)- short-lived creeping shoots used for vegetative propagation. Found in many plants (drupes, bentgrass, strawberries). They usually lack developed green leaves, their stems are thin, fragile, with very long internodes. The apical bud of the stolon, bending upward, produces a rosette of leaves that easily takes root. After the new plant takes root, the stolons are destroyed. The popular name for these above-ground stolons is mustache.
spines- shortened shoots with limited growth. In some plants they form in the axils of the leaves and correspond to the side shoots (hawthorn) or are formed on the trunks from dormant buds (locust locust). Characteristic for plants in hot and dry growing areas. Perform a protective function.
Succulent shoots- aboveground shoots adapted to accumulate water. Typically, the formation of a succulent shoot is associated with the loss or metamorphosis (transformation into spines) of leaves. The succulent stem performs two functions - assimilation and water storage. Characteristic of plants living in conditions of prolonged lack of moisture. Stem succulents are most represented in the cactus and euphorbia family.
