Modifications of plant organs. Leaf modifications

If the roots, in addition to the main functions, perform any additional ones, then they undergo corresponding changes in the external and internal structure.

Roots can serve as an organ that stores nutrients. Such roots are strongly thickened. If the reserve substances accumulate in the main root, then root crops are formed, for example, such as in carrots and beets.
If thickenings occur in adventitious roots, then they are called root cones, or root tubers. Root tubers are formed in dahlia, Jerusalem artichoke, meadowsweet.

The roots of higher plants also enter into symbiosis with fungi and form the so-called mycorrhiza. Mycorrhiza is ectotrophic and endotrophic. In the first case, the fungus only covers the root from the outside, replacing root hairs with it. With endotrophic mycorrhiza, hyphae penetrate into the root cells (in orchids). It is assumed that fungi produce enzymes that dissolve cell storage products and soil organic matter.

Root modifications. As a result of acquiring new functions, organs are able to change.

Root crop - thickening of the main root, associated with the deposition of a supply of nutrients in it (carrots, beets, radishes, etc.).
Root tubers (root tubers) - thickening of lateral or additional roots associated with the deposition of a supply of nutrients (yam, dahlia, etc.).

Respiratory roots (pneumatophores). These are lateral roots that grow upward and rise above the surface of the water, soil. Formed in plants (mangrove trees) that grow on excessively moist soils, swamps, with a low oxygen content. Therefore, plants with the help of such roots receive oxygen directly from the air. The respiratory roots are rich in aerenchyma.

Trailer roots. These are additional short roots that develop on plants with a climbing stem (ivy, tenacious ficus, etc. - note .. The roots grow on the stem. With their help, the plant clings to cracks, supports and rises higher.

Supporting roots. They are found in large trees (elm, beech, poplar, tropical, etc.). They are lateral roots. On the lateral roots, which run near the soil surface, flat triangular and vertical aboveground processes adjacent to the trunk develop, which resemble boards leaning against trees.

Retractable, or contractile roots. In some plants, there is a sharp reduction in the root in the longitudinal direction at its base (for example, in plants that have bulbs). Retractable roots are common in angiosperms. They cause rosettes to lie firmly on the ground (for example, in plantain, dandelion, etc.), the underground position of the root neck and vertical rhizome, and provide some deepening of the tubers. Thus, retractable roots help shoots to find the best depth in the soil. Retractable roots in the Arctic ensure that flower buds survive the unfavorable winter period.

Sheet modification

The leaves of different plants are very diverse in their structure and functions.

The reasons leading to the appearance of leaf modifications may be different. The main one is the growing conditions. Thus, tropical rainforest plants (for example, ficus, begonia, philodentron) have large leaves that evaporate a lot of water. The leaves of plants in most arid habitats are adapted to reduce evaporation. For example, in a cactus, the leaves have turned into thorns, and in shoots, the function of water storage begins to predominate. Plants with such shoots are called succulents (lat. succus - juice, juicy). In succulents, water can be stored in the stems (stem succulents) or in the leaves (leaf succulents). In some plants (celery, rhubarb) leaf petioles are modified, which become thick and fleshy; they store nutrients.

Leaf modifications

In those plants that grow near water bodies, for example, in nature, common reed, the so-called "lotus effect" is observed. This manifests itself as an extremely low wettability of the surface of the leaves of these plants. When water gets on the leaves or petals of these plants, spherical drops are formed, which, flowing down from the leaf, carry away dirt and dust, thereby cleaning the surface of the leaf blade. The appearance of this effect is due to the peculiarities of the microscopic structure of the leaf of plants of the genus Lotus.

Many deciduous trees have heavily indented leaves, such as the maple. This device allows you to withstand strong gusts of wind.
Plants that grow in arid climates have many adaptations for survival in dry climates. favorable conditions. This is a hairline on the leaves, which is able to retain moisture and prevent its evaporation. The wax coating on the leaf blade of some plant species performs the same function. The shiny surface of large flattened ficus leaves from the Mulberry family tends to reflect sunlight. These plants are native to Southeast Asia, where the climate is arid and hot.

Also, almost all types of cacti are adapted to long dry periods. Therefore, these plants have leaves transformed into spines to reduce water evaporation and protect against pests. In cacti, the function of photosynthesis passes from leaf to stem, which, together with a decrease in leaf size, prevents moisture loss. Those plants that naturally grow in well-lit places have developed such an adaptation on the leaves as translucent windows that act as a filter of light before it reaches the inner layers of the leaf. This is what happens in fenestraria. In the fleshy succulent leaves of aloe, stonecrop accumulates water, which the plant's body consumes with a lack of moisture in the external environment. In the same way, onion leaves have transformed into a bulb, which helps the plant retain water and nutrients.

The leaves of some plants have teeth along the edges. This adaptation is necessary, as it increases the severity of the processes of photosynthesis and transpiration (during which the temperature in these departments decreases - approx. site). This leads to condensation of moisture on the points of the leaves and the formation of dew drops.
The leaves of many plants are transformed during evolution in order to protect the plant from destruction by other living organisms. So, pheromones, poisons, aromatic oils can be produced in the leaves, for example, in eucalyptus. And the leaves of other plants include crystallized minerals, which repels herbivores.

In peas, ranks, some types of peas, antennae appeared from leaves transformed in the process of evolution. Such a device serves to enhance the supporting function of the plant stem. The plant, clinging to the supports with its antennae, rises up, carrying the leaves to the light.

Modified leaves of some plants have been transformed into petals for better pollination by insects that are attracted to these parts of the plant's body. And the transformation of leaves into false flowers and cover leaves allows you to replace the missing organs in milkweed.
Predatory plants live on soils that are poor mineral salts. In total there are about 500 species. The most famous plants are: sundew, zhiryanka, rosolista, venus flytrap, nepentis.

The last plant that lives in tropical forests is able to catch not only insects, but even small animals - mice, frogs, reptiles.

Sundew and pemphigus have become carnivorous plants by transforming their leaves into trapping devices for the insects that the plants feed on.

In carnivorous plants (sundew (Drosera), zhyryanka, rosolista, etc.), the leaves are covered with numerous glands that secrete a sticky transparent liquid that attracts insects and sticks them to the leaf. When an insect falls into a trap, the secretions from the glands increase in the plant; at the same time, the glandular hairs bend towards the body of the insect (sundew) or the edges of the trapping leaf on which it is located (syryanka) are wrapped. In other plants, the trapping apparatus is either passively trapping insects (Nepenthes, Sarracenia, Darlingtonia, etc.) or active traps (Dionea, Aldrovand, pemphigus, etc.).

Thus, due to the modification of leaves, plants adapt to existence in adverse environmental conditions.

The plant consists of a root, stem, leaves, inflorescences and fruits. Stems, buds and leaves form a vegetative organ - an escape. Modifications of plant shoots contribute to the supply of nutrients, reproduction, and protection.

What it is?

The desire to survive in certain conditions changed the structure of the shoots. A tendril, a tuber, a thorn are the result of such changes. Examples of shoot evolution are well observed in agricultural plants. Allocate underground and above-ground shoots.

Elevated

Modifications of above-ground shoots are manifested in the form of compaction, lignification, a significant expansion of the entire shoot or its individual parts. The types and functions of transformations of aboveground shoots are briefly described below.

• spines . Lumbering lateral shoots without leaves. The sharp end provides protection against being eaten. The thorns are different from the thorns found in some representatives of the Rosaceae family (rose hips, raspberries, roses). A thorn is an outgrowth of the integumentary tissue of the stem, not tied to a specific part of the shoot. The spines develop in the axils of the leaves or from dormant buds. Sometimes these are modified leaves. May be simple or branched. Examples are hawthorn, yellow acacia, barberry.

Rice. 1. Acacia thorns.

• tendrils . Long lateral shoot without leaves. It can twist into a spiral at the end or branch. The antennae perform a supporting function: the plant clings to objects, rising from the ground. Inherent in plants of the Cucurbitaceae family (cucumber, watermelon, pumpkin), grapes and blue passionflower.
• Above ground stolons .

  They are called mustaches (not to be confused with antennae). Often formed in spring and are reproductive organs. Depart from the base of the stem and spread along the ground. A new plant grows from the top of the mustache. Roots extend from the lower part, and shoots with short internodes from the upper part, forming rosettes. During the year, the stolons die off, and the young plant puts out its own whiskers. Typical representatives are strawberries, strawberries, creeping tenacious.

• Claudius . This is a lateral wide, often fleshy shoot resembling a leaf. Contains chlorophyll and performs the function of photosynthesis. Capable of continuous growth. Some plants develop spines from cladodium buds. Examples are the Decembrist cactus, prickly pear, southern carmichael, Mühlenbeckia flatflower.



Rice. 2. Opuntia.

• Phyllocladius . In origin and function, it resembles a cladodium, but has limited growth. It is located in the axils of scaly leaves. In some cases, it is outwardly difficult to distinguish phyllocladium from ordinary leaves. Examples are phyllanthus, needle, some plants of the genus Asparagus.
• pseudobulb . Also called ground tuber. It develops in representatives of the Orchid family and kohlrabi. It is a seal above the ground. Can run away.

In peas, leaves are modified into tendrils, and not whole shoots.

Underground

Underground modifications of shoots play the role of a store of nutrients in case of adverse conditions, and are also organs of vegetative reproduction. The structural features of underground shoots are shown in the table.

Type of escape	Structural features	plant examples
Rhizome	Elongated compacted form. It has scaly leaves, buds, adventitious roots. May branch.	Iris, May lily of the valley, couch grass, coltsfoot
	Round shape. On the surface are "brows" (scars from dead leaf scales) and "eyes" (buds).	Potato, Jerusalem artichoke, Corydalis
Bulb	The stem is transformed into a bottom, from which fibrous roots develop. From the buds of the bottom, fleshy scales extend, covering the inner shoot growing upwards.	Tulip, onion, narcissus, lily

The leaf is an obligatory vegetative organ of the vast majority of plant organisms. For the first time we get acquainted with its structure by studying the higher spore plants - mosses, which have leaf-stem forms.

These include, for example, sphagnum and cuckoo flax. Being the lateral parts of the shoot, the leaves usually consist of a leaf blade and petiole, which are attached to the stem. They perform the most important functions: they serve as the main organs that carry out photosynthesis, transpiration (evaporation of water) and respiration. If, for some reason, these vegetative organs are forced to take on other functions, then the plant undergoes a modification of the leaves. In our article, we will find out what conditions lead to the emergence of an atypical structure and special properties of leaf blades in higher spore, gymnosperms and flowering plants.

Influence of abiotic factors on the morphological characteristics of the organism

Habitat conditions are powerful shaping forces that can radically change external structure both plants and animals. The adaptations that arise in them are adaptive in nature and were well studied by Ch. Darwin. The scientist considered their appearance the result of the action of the struggle for existence - one of the driving factors of natural selection. It is from this position that modern biology explains the modification of leaves observed in some biological species. Everyone knows examples illustrating the structural features of xerophyte organisms. Forced to live in an environment where water is the limiting factor, plants of the southern steppes, semi-deserts and deserts have a low transpiration coefficient.

It is explained by a decrease in the evaporating area of ​​leaf blades. In the end, the modification of the leaves reaches such a level in xerophytes that they turn into thorns, for example, in saxaul or cacti. The transition of leaves into scales that have lost the ability to photosynthesize in horsetails has the same reason.

How do leaves perform a supporting and protective function

From the course of botany it is known that such parts of the plant as the root and stem have mechanical properties. The tissues of the leaf blade do not have a sufficiently developed system of reinforcing elements, with the exception of the vascular-fibrous bundles located in the veins. However, for some plant species with a climbing stem shape and a weak, superficial type of root system, a special leaf structure is inherent. The modification of leaves, for example, in peas, is expressed in the appearance of tendrils that perform a supporting function and fix the stem in space. The property of protection from adverse conditions is characteristic of dry leaves - scales of bulbs or buds of flowering plants, covering the delicate rudimentary leaves.

carnivorous plants

Exotic representatives of the flora: nepenthes and sundew - feed heterotrophically, like animals. The modification of their leaves is associated with new functions: to catch and further digest small insects stuck to the walls of leaf blades. They are covered with sticky trap hairs that firmly hold the victim. Interestingly, predator plants usually live on soils with a low nitrogen content, the lack of which they more than make up for at the expense of obtained animal proteins.

Examples of modification of the leaves of gymnosperms and flowering plants

Everyone knows the fact that representatives of the Coniferous class are easily recognizable by the needle structure of their leaves, called needles. It has a small surface and deep-seated stomata, covered with a layer of wax in winter. All this helps pine, larch, cedar to minimize water loss during the cold period. Flowering plants, such as aloe and juvenile, conserve moisture in a different way. Their leaves, on the contrary, become fleshy and succulent reservoirs in which water is stored all year round.

Some types of angiosperms (cacti, acacia, barberry) use their leaves-thorns as weapons. It protects the plant from mechanical damage or being eaten by animals. Many examples can be cited illustrating the modification of leaves in various biological species that form the modern flora of the Earth. All of them are various kinds of adaptations aimed at the survival of plants in various environmental conditions.

1) Botany is the science of plants.It studies the life of plants, their structure, vital activity, living conditions, origin and evolutionary development. This is part of the tasks of botany, but, in addition, the task is to study the plant world both separately and on a large scale.

The role of plants in nature:
1. Participate in the formation of organic substances, accumulate in the products of photosynthesis a large number of chemical energy.
2. Maintain the level of oxygen in the atmosphere. Prevent the accumulation of excess carbon dioxide in the atmosphere.
3. They play a leading role in the circulation of mineral and organic substances, which ensures the continuous existence of life on Earth.
4. Reduce the greenhouse effect, reduce the temperature to the current level.
5.Vegetation takes an active part in the formation of soils.
6. Prevent soil erosion, fix ravines and mountain slopes.

The role of plants in human life:
1.Used for food.
2. Medicinal plants.
3.Technical plants used in industry as raw materials.
4. Plants as a source of vitamins.
5. Aesthetic value - they decorate our lives, bring joy.

2) Androecium- a collection of stamens in a flower. The stamen consists of a filament and an anther. The anther has 2 thecae, each thecae has 2 microsporangia or a pollen nest.

There are 2 processes in the anther:

• microsporogenesis- the process of formation of male microspores in microsporangia

• 2) Microgametogenesis- development from microspores of a male gametophyte or pollen grain. The microspore divides by mitosis, resulting in the formation of two cells. They represent the male gametophyte or pollen grain.

  One of the cells of the pollen grain is called vegetative and is capable of forming a long process, or pollen tube, reaching the embryo sac. The second (generative) cell, floating in the cytoplasm of a vegetative cell, when dividing, gives two male gametes - flagellated spermatozoa or flagellated spermatozoa. The spermatozoa reach the egg through the archegonial canal. Sperm, moving along the pollen tube, reach the embryo sac and participate in fertilization.

3) root metamorphosis.

Metamorphosis is a deep transformation of the structure of the body that occurs in the course of individual development.

1) Storage roots. They are usually thickened. Strongly thickened adventitious roots are called root cones, or root tubers. Many, more often biennial, plants with a tap root system develop a formation called root crop. Both the main root and the lower part of the stem take part in the formation of the root crop.

2) Many bulbous and rhizomatous plants form retractors roots. They can shorten and draw the shoot into the soil to the optimum depth during the summer drought or winter frosts. Retracting roots have thickened bases with transverse wrinkling.

4) Respiratory roots, or pneumatophores are formed in some tropical woody plants living in conditions of lack of oxygen. Pneumatophores grow vertically upwards and protrude above the soil surface. Through a system of holes in these roots, connected with the aerenchyma, air enters the underwater organs.

5) In some plants, to maintain shoots in the air, additional support roots. They depart from the horizontal branches of the crown and, having reached the soil surface, branch intensively, turning into columnar formations that support the crown of the tree ( columnar banyan roots) . stilted roots extend from the lower parts of the stem, giving the stem stability. They are formed in mangrove plants, plant communities that develop on tropical oceans flooded at high tide, and also in corn. Ficus rubbery are formed plank-shaped roots. Unlike columnar and stilted, they are by origin not adventitious, but lateral roots.

The roots of many plants form a symbiosis with hyphae of soil fungi, called mycorrhiza. Mycorrhiza is formed on sucking roots in the absorption zone.

There are two main types of mycorrhiza: 1) external (surrounds the outside. In many edible mushrooms) 2) internal (The mushroom component makes it easier for the roots to obtain water and mineral elements from the soil, often fungal hyphae replace root hairs. In turn, the fungus receives carbohydrates and other nutrients from the plant. )

On the roots of legumes, special formations appear - nodules in which bacteria from the genus Rhizobium settle. These microorganisms are able to assimilate atmospheric molecular nitrogen, converting it into a bound state. Part of the substances synthesized in the nodules are absorbed by plants, bacteria, in turn, use the substances found in the roots. This symbiosis has great importance for agriculture. Legumes are rich in protein due to the additional source of nitrogen. They provide valuable food and fodder products and enrich the soil with nitrogenous substances.

Escape metamorphoses.

Underground:

1) rhizome - a long-lived underground shoot that performs the functions of deposition of reserve nutrients, renewal, and sometimes vegetative propagation.
2) stolons - short-lived thin underground shoots bearing underdeveloped scaly leaves. Stolons serve for vegetative reproduction, settlement and territory capture. Spare nutrients are not deposited in them.
3) the tuber has a spherical or oval shape, the stem is strongly thickened, reserve nutrients are deposited in it, the leaves are reduced, and buds form in their axils. The stolons die off and are destroyed, the tubers overwinter, and on next year give rise to new above-ground shoots.
4) bulb - an underground shoot with a very short flattened stem and scaly fleshy succulent leaves that store water and soluble nutrients, mainly sugars.
5) The corm looks like an onion, but its scaly leaves are not storage; they are dry, and reserve substances are deposited in the thickened stem part (saffron, gladiolus).
b) Caudex is a perennial organ of shoot origin of perennial herbs and shrubs with a well-developed taproot that persists throughout the life of the plant. Together with the root, it serves as a place of deposition of reserve substances and carries many renewal buds, some of which may be dormant (dandelion, wormwood)

Overground:

1) stolons - short-lived shoots, the function of which is vegetative reproduction, resettlement and territory capture.
2) Water storage organs can be leaves or stems, sometimes even buds. Such succulent plants are called succulents (aloe, agave, crassula, rhodiola, or golden root).
3) Head of cabbage - a succulent organ that forms in ordinary cultivated cabbage. The adaptive form of the head of cabbage arose as a modification of a part of the rosette.
4) The spines of cacti are of leaf origin. Leaf spines are often found in non-succulent plants (barberry). In many plants, spines are not of leaf, but of stem origin (wild apple, wild pear).
5) Tuber - a thick near-earth part of the stem in representatives of the orchid family. Serves plants as a special organ for storing water and nutrients.
b) Cladodium - a modified lateral shoot with the ability to grow long, with green flat long stems that act as a leaf. As an organ of photosynthesis, the cladodium has a well-developed chlorophyll-bearing tissue.
7) Phyllocladium - a modified leaf-like flattened lateral shoot with limited growth and performing the functions of a leaf. Phyllocladia develop from lateral buds, so they are always found in the axil of a small membranous or scaly leaf. Performing the function of photosynthesis.
8) Antennae - a flagellate branched or unbranched shoot of a metameric structure, typically devoid of leaves. Stem tendrils, as a highly specialized shoot, perform a supporting function (cucumber, watermelon)

Leaf metamorphosis:

1. spines- one of the most common modifications; they serve as a defense against being eaten by animals. In this case, the leaf either completely turns into a thorn (cacti, euphorbia, barberry, white locust, camel thorn), or part of it turns into a thorn (thistle, thistle, holly).

2. tendrils(in compound leaves of some plant species) cling to a support, carrying the entire shoot to the light. At the same time, either the upper leaves of a complex leaf (pea, vetch), or the entire leaf can turn into a tendril, and the stipules (some types of ranks) perform the function of photosynthesis.

3. The storage function is performed juicy scales bulbs (onion, garlic), aloe leaves, head of cabbage.

4. Covering scales buds protect delicate rudimentary leaves and growth cone from adverse environmental conditions.

5. trapping devices provide the life of insectivorous plants in swamps in conditions of a lack of nitrogen and other elements of mineral nutrition. The leaves of such plants have changed beyond recognition, turning into traps (Venus flytrap), jugs (nepenthes). The leaves of some plants with their shiny, brightly colored droplets on the hairs attract ants, flies, mosquitoes, and other small insects; the juice released at the same time contains digestive enzymes (dew).

Typically, a sheet performs three functions:
- photosynthesis (organic nutrition);
- transpiration (evaporation of water);
- gas exchange with the environment.

But there are times when a leaf takes on additional functions that are not characteristic of it. Then its structure changes dramatically, and we are again talking about modifications .
1. If the stem of the plant is weak, then the leaf can perform a supporting function, clinging to surrounding objects. For example, the antennae of a pea.
2. In cacti, the leaves are modified into thorns. this form of the leaf allows you to drastically reduce the evaporation of water and protects against being eaten by animals.

Barberry spines are also modified leaves

3. Leaves-traps are typical for "predatory" plants. perhaps this is the most interesting and exotic modification. Oddly enough, the leaves change into "traps" not because the plant craves the blood of the victims, but because it grows on extremely mineral-poor soils. For example, our "compatriot" Rosyanka lives in peat bogs, where there is no soil at all.

So you have to get the minerals necessary for life from the bodies of various insects. And no one canceled photosynthesis in such plants. Therefore, their type of nutrition can be called mixotrophic.

4. Sometimes the leaves surrounding the flowers and entire inflorescences are bright, conspicuous, such as white or red cobs in aronnikovye (calla, anthurium) or red, white and pink apical leaves in poinsettia. They are easily mistaken for petals, while the true flowers of these species can be relatively small and inconspicuous.

Leaf modifications

Some plants change (and often quite significantly) the structure of the leaves for one purpose or another. Modified leaves can perform the functions of protection, storage of substances, and others. The following metamorphoses are known:

Leaf spines - may be derivatives of the leaf blade - lignified veins (barberry), or stipules (acacia) can turn into spines. Such formations perform a protective function. Spines can also be formed from shoots (see Modifications of stems). Differences: spines formed from shoots grow from the axils of the leaf.

Antennae are formed from the upper parts of the leaves. They perform a supporting function, clinging to surrounding objects (example: China, peas).

Phyllodes are petioles that take on a leaf-like shape and carry out photosynthesis. In this case, the true leaves are reduced.

Trapping leaves are modified leaves that serve as trapping organs of carnivorous plants. Catching mechanisms can be different: droplets of sticky secretion on the leaves (dew), vesicles with valves (pemphigus), etc.

Saccular leaves are formed due to the fusion of the edges of the leaf along the midrib, so that a bag with a hole at the top is obtained. The former upper sides of the leaves become inner in the bag. The resulting container is used to store water. Through the holes, adventitious roots grow inward, absorbing this water. Sack-shaped leaves are characteristic of the tropical liana Raffles dyschidia

Succulent leaves - leaves that serve to store water (Aloe, agave).

Similar organs (in plants)

The morphology of plants presents many examples of similar organs, i.e., such formations, the origin of which is different, but the functions are the same. So, the roots are similar to rhizoids, the spines are thorns, the seeds are spores. The similarity of functions often causes a great similarity of the external form. So, in the case of underdevelopment of leaves, the stems, which take over the work of assimilation, usually become flat and wide, acquiring a resemblance to leaves. Particularly interesting are the assimilating stems (cladodia or phylocladia) in Ruscus species. Here, the cladodia are so similar to leaves that for a long time there were disputes whether they were leaves or stems. In the same way, tubers are similar, whether they come from stems or roots, thorns and tendrils are similar, whether they come from leaves or from whole branches.

Homologous organs (Greek "homos" - the same) - organs that are similar in origin, structure, but perform different functions. Their appearance is the result of divergence. An example of homologous organs in animals is the forelimbs, consisting of the same bones, having the same origin, but performing different functions: in amphibians, reptiles, in most animals they serve for walking, in birds - for flying, in whales - for swimming, in mole - for digging the earth, a person performs the finest operations in the labor process. In plants, the homologous organs are the fern growth, the primary endosperm of the pine ovule, and the embryo sac of the flowering plant. All of them are formed from spores, have a haploid set of chromosomes and carry a female gamete - an egg. But the fern growth is an autotrophic plant with archegonia. The primary endosperm of the pine is part of the ovule, and then the seed as a storage tissue. The formed embryo sac has eight cells, and only three of them take part in the development of the seed, the rest die off. Homologous organs indicate that in the course of adaptive evolution, traits undergo profound changes that lead to the formation of new species, genera, and larger systematic groups of animals and plants.

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Botany. Biology

Questions and answers for the exam in botany Biology. Morphology of plants. The structure of the root, Shoot, Stem, Leaf. Plants

This material includes sections:

Morphology of plants as a branch of botany. Tasks and directions of development

The main vegetative organs of a higher plant, their growth, branching, polarity and symmetry

Root, define. Root functions

Classification of roots by origin, in relation to the substrate

Structure of young root zones

Root systems and their classification. Types of root systems

Escape, define. Vegetative and generative shoots, elongated and shortened shoots

What organs are part of the shoot, and what functions do they perform?

Classification of shoots according to the nature of their location in space

Name the main types of shoot branching. Why is the sympodial type considered productive?

Stem, define. Stem cross-sectional shapes. The main functions of the stem

Morphology and classification of stem types

Kidneys and their types depending on the structure. Types and functions of kidneys depending on their position on the shoot

Types of kidneys by origin

Morphological diversity of the stem

Metamorphosis, define. root metamorphosis

Above-ground modification of shoots, their distinctive features, diversity and biological significance

Underground modification of shoots, their structure, diversity, biological significance, distinctive features

List, define. The structure and functions of the leaf

List, define. Variety of leaves and leaf formations

List, define. Forms of leaf blades, the main types of vein coriation of leaves of angiosperms

General characteristics and distinctive features of the sheet. The emergence of the leaf in the process of revolution

Leaf parts and their functions. The leaves are simple and compound. Edge character, general shape

Morphology of plates of simple leaves or compound leaves, nature of the edge, general shape

Morphology of simple leaf blades or compound leaflets

Leaf arrangement and its variants. The main patterns of leaf arrangement. Leaf mosaic

Leaf lifespan. Evergreen and deciduous plants. Biochemical and morphological preparation of plants and its biological significance

The structure of a plant seed. Morphological types of seeds

Conditions necessary for seed germination. Seed dormancy and its biological significance

Variety of leaves within a single plant. Layered categories of leaves. Heterophilia

Modifications of leaves or parts of leaves, their structure and biological significance. Examples of apalogous and homologous organs in plants

General ideas about the reproduction of higher plants. Comparative characteristics of different types of reproduction, their biological significance for higher plants

Methods of natural and artificial vegetative propagation of plants. The economic importance of vegetative propagation of plants

General characteristics of a flower. Organs and parts of a flower, their functions and formation in the process of flower ontogenesis

Very diverse in their structure and functions. Leaf modifications due to the fact that in the process of evolution, the leaves adapted to various climatic factors, depending on the growing conditions of plants.

In those plants that grow near water bodies, for example, in naturia, common reed, there is a so-called "lotus effect". This manifests itself as an extremely low wettability of the surface of the leaves of these plants. When water gets on the leaves or petals of these plants, spherical drops are formed, which, flowing down from the leaf, carry away dirt and dust, thereby cleaning the surface of the leaf blade. The appearance of this effect is due to the peculiarities of the microscopic structure of the leaf of plants of the genus Lotus.

Many deciduous trees have heavily indented leaves, such as the maple. This device allows you to withstand strong gusts of wind.

Plants growing in arid climates have many adaptations to survive in adverse conditions. This is a hairline on the leaves, which is able to retain moisture and prevent its evaporation. The wax coating on the leaf blade of some plant species performs the same function. The shiny surface of large flattened ficus leaves from the Mulberry family tends to reflect sunlight. These plants are native to Southeast Asia, where the climate is arid and hot. Also, almost all types of cacti are adapted to long dry periods. Therefore, these plants have leaves transformed into spines to reduce water evaporation and protect against pests. In cacti, the function of photosynthesis passes from leaf to stem, which, together with a decrease in leaf size, prevents moisture loss. Those plants that naturally grow in well-lit places have developed such an adaptation on the leaves as translucent windows that act as a filter of light before it reaches the inner layers of the leaf. This is what happens in fenestraria. In the fleshy succulent leaves of aloe, stonecrop accumulates water, which the plant's body consumes with a lack of moisture in the external environment. In the same way, onion leaves have transformed into a bulb, which helps the plant retain water and nutrients.

The leaves of some plants have teeth along the edges. This adaptation is necessary, as it increases the severity of the processes of photosynthesis and transpiration (during which the temperature in these departments decreases). This leads to condensation of moisture on the points of the leaves and the formation of dew drops.

The leaves of many plants are transformed during evolution in order to protect the plant from destruction by other living organisms. So, pheromones, poisons, aromatic oils can be produced in the leaves, for example, in eucalyptus. And the leaves of other plants include crystallized minerals, which repels herbivores.

In peas, ranks, some types of peas, antennae appeared from leaves transformed in the process of evolution. Such a device serves to enhance the supporting function of the plant stem. The plant, clinging to the supports with its antennae, rises up, carrying the leaves to the light.

Modified leaves of some plants have been transformed into petals for better pollination by insects that are attracted to these parts of the plant's body. And the transformation of leaves into false flowers and cover leaves allows you to replace the missing organs in milkweed.

Sundew and pemphigus turned into predatory plants due to the transformation of the leaves, which became trapping devices for insects that the plants feed on.

Thus, due to the modification of leaves, plants adapt to existence in adverse environmental conditions.

Common modifications of shoots of angiosperms are rhizomes, bulbs and tubers. Usually they are formed in perennial herbaceous plants as organs in which reserve nutrients are deposited. In such plants, green aerial parts die off for the winter, but modified shoots remain in the soil. In the spring, due to the nutrients contained in them, the plants again develop ordinary above-ground shoots.

In addition to storing nutrients, modified shoots perform another function. With their help, plants can reproduce vegetatively.

Rhizome

Modified Escape rhizome found in many perennial plants (nettle, lily of the valley, couch grass, etc.). The rhizome is located in the upper layers of the soil, resembles a root, but spreads horizontally.

The rhizome is a shoot, as it has apical and axillary buds, as well as leaves that are modified into scales. The resemblance to the root of the rhizome is given by adventitious roots that grow from it along the entire length.

During the growing season, the plant deposits reserve nutrients in the rhizome. At their expense, new young shoots grow from the buds of the rhizome next year.

With the help of parts of the rhizome containing buds and roots, vegetative propagation of plants is possible.

Bulb

Modified Escape bulb characteristic of onions, tulips, lilies and other plants. At the bottom of the bulb there is a flattened stem called bottom. Leaves of two types modified into scales grow from the bottom. The outer leaves are changed into dry scales that perform a protective function. The inner thick and juicy scales contain spare nutrients (bulbs contain many different sugars among other substances) and water. The bulbs also grow buds from the bottom.

In favorable conditions, adventitious roots grow from the bottom of the bulb, resulting in the formation of a fibrous root system. Buds can grow into shoots, but they can also develop into so-called baby bulbs. Each such bulb can give rise to a separate new plant. Thus, vegetative reproduction is carried out with the help of bulbs.

Tuber

Modified Escape tuber can be observed in plants such as potatoes and Jerusalem artichoke, as well as some others.

The tuber is formed at the top of another modified shoot - stolon. Stolons grow from the lower parts of above-ground shoots and go into the soil. Organic substances synthesized by the green parts of the plant during photosynthesis move along the stolons to their tops, and thus tubers are formed here. Tubers accumulate a lot of starch.

A tuber is at least modified, but an escape. It has short but thick internodes and many buds called eyes. The leaves of the tubers are reduced. The eyes are located in the recesses of the tuber, and in each such recess there may be several bud eyes.

The part of the tuber that is connected to the stolon is called the base of the tuber. On the opposite side of the base is the top of the tuber. Glazkov is closer to the top. Most often, the apical eye-bud develops into a young green shoot.

spines

Spines are also modifications of plant leaves. They are characteristic of those that grow in arid and desert conditions. Everyone has seen cactus thorns. These are its leaves. In conditions of lack of moisture, when the transpiration process must be minimized, this is an ideal adaptation. With such a small surface of the leaf blade and water, very little will evaporate.

However, the spines of cactus and acacia are a different modification of the leaves. What's the Difference? In white acacia, hawthorn, blackthorn, barberry and other similar plants, the spines are modified stipules, and not the plates themselves. Their main function is to protect fragrant flowers and sweet fruits from being eaten by various animals.

needles

The needles of all representatives of the department of gymnosperms are also a modification of the leaves. Everyone remembers the children's riddle about the Christmas tree - "in winter and summer in one color." And all conifers are evergreen in many respects precisely due to the characteristic modifications of the leaves. In cross section, they have a rounded or ribbed shape. Such leaves have a small area, like the spines of cacti. Their stomata, through which gas exchange occurs, are immersed in the integumentary and main part of the leaf. This reduces the rate of water evaporation. In the winter season, these formations are completely sealed with wax, which reduces transpiration to almost zero. Therefore, at a time when all angiosperms shed their leaves for the winter, coniferous trees and shrubs boast lush green decoration.

Leaves of desert plants

It is not easy for plants to survive in arid conditions. What causes the modification of leaves in these plants? They need to have such structural features that will allow them to survive with sudden changes in temperature and lack of moisture. Therefore, their leaves are often covered with a thick layer of hairs, or a waxy coating. They protect plants from excessive moisture loss. There is another device as well. Many types of arid ecosystems store water in thick, fleshy leaves. An example of such a modification is aloe, which is often bred as indoor plant having healing properties.

tendrils

To consider the features of the following organs, let's recall what leaf modifications are found in the legume family. The shoots of most of them are long and thin, and the fruits, when ripe, acquire a mass that does not allow them to stay upright. But it is the most beneficial for the productive implementation of photosynthesis. What leaf modifications are found in peas? Of course, these are mustaches. This is how individual plates from a complex sheet are modified. With their help, the plant clings to the support, and as a result, a weak and thin stem is located in the required position.

Scales

To understand why kidney scales are a modification of the leaf, it is necessary to understand the structure of the bulb. Consider it on the example of a common leek. Its bulb, despite the fact that it is located underground, is a modification of the above-ground part of the plant - the shoot. This is easy to prove. The shoot consists of a stem, leaves and buds. The same parts are in the bulb. Its flat stem is called the bottom. A bundle of adventitious roots departs from it. Above are several types of leaves. Young have green color and grow from the kidneys located on the bottom. Juicy and fleshy leaves take on this form in order to store moisture. With its help, the plants in which the bulb is formed, endure drought underground, low temperatures and other adverse events. And dry scales, which are also a modification of the leaves, protect the internal contents of the bulb from mechanical damage.

predatory leaves

Leaf modification can also be very dangerous for other living beings. There is a whole group of insectivorous plants. They are also capable of carrying out the process of photosynthesis, that is, they are autotrophs. But if there are no conditions for its occurrence, then they switch to a heterotrophic mode of nutrition. With the help of modified leaves, they catch insects and digest them. For example, in the tropical plant sarracenia, the leaves are a funnel that borders fragrant nectaries. They also attract insects. Approaching, the victim begins to slide along the edges of the funnel and is trapped. In addition, the leaves also secrete special narcotic substances that immobilize insects of any size. On top of the funnel, the sheet is twisted in the form of a hood. This fold prevents rain from getting inside, mixing with digestive enzymes.

Leaf modifications also include the movable tentacles of the sundew, at the ends of which there is a sticky liquid. It attracts insects that land to feast and become trapped.

leaf buds

All leaves are vegetative organs. With their help, the process of asexual reproduction is carried out. For example, if you separate a leaf of an uzambar violet from an adult plant and place it in a container of water, after a while it forms a root. But in a number of plants, the process of reproduction occurs differently. So, at the room Kalanchoe, along the edge of the leaf blade, there are buds, from which young shoots develop independently. They are almost fully formed: they have a small root and leaves. Falling off, they germinate in the same container as an adult plant. This process is also called self-reproduction.

The value of modifications of plant leaves is great. These adaptations increase vitality and facilitate the process of adaptation. Thanks to the modifications of the leaves, land plants were able to master various climatic zones, differing in the level of moisture, temperature and soil properties. In addition to photosynthesis, transpiration, and cellular respiration, leaf modifications allow them to perform other important functions: protection from predators and mechanical damage, regulation of gas exchange and the level of water evaporation, and heterotrophic nutrition.