Modifications, or metamorphoses, are widely observed in all living organisms. All vegetative organs of the plant are subject to changes.

Modifications of the sheet are associated with the performance of different functions.

Thorns perform a protective function. The origin of the thorn can be determined by its position on the stem of the plant. In barberry, a thorn of leaf origin is located under the leaf, in contrast to a thorn of shoot origin in hawthorn, which is located in the leaf axil. Leaf origin

thorns and cacti. They are characteristic of plants in arid habitats, and various parts of the leaf undergo modification. So, in astragalus, the rachis of a complex leaf is modified into a thorn, in white acacia - stipules. In the thistle, individual parts of the leaf blade are modified.

The shoots of lianas have devices that help them to hold on to some kind of support in order to take a certain position in space. In peas and ranks, part of the leaf is modified into tendril, which helps them cling to the support. Have bulbs of many plants, the bulk of them are storage leaves (hazel grouse, curly lily). Bulbs of bulbous plants are formed different kind modified leaves. So, in onion, leaves of the lower formation and thickened bases of green leaves take part in the formation of a bulb. The size of the modified leaves that store the scales in the bulbs is different. In hyacinth and tulip, they are wide, in lily - narrow, slightly

Covering each other. The leaves of leafy succulents perform a water-storing function (aloe, agave).

Fishing apparatus- the most interesting leaf modifications characteristic of insectivorous plants (sundew, flycatcher, nepentes, etc., Fig. 109). The leaves of these plants look like jugs, urns, slamming sticky plates. Insects caught in them under the action of enzymes decompose and are consumed by the plant. This nutritional characteristic is characteristic of these plants because they often grow in places where the soil is low in minerals. Thus, the nutrition of these plants is heterotrophic, living organisms, which, under these conditions, contributes to their better growth and development. In a plant of fresh water bodies - pemphigus, parts of a strongly dissected leaf are transformed into trapping bubbles, where small algae and animals fall (Fig. PO), after which the bubble is closed with a valve. The extraction is "digested" by enzymes.

Such saccular leaf modifications are found not only in insectivorous plants. In an epiphytic plant of a humid tropical forest, individual leaves of the washidia are modified into saccular formations, where water and humus accumulate (Fig. 111). Adventitious roots are formed in the leaves, supplying plants with moisture.

The main functions of the leaves are photosynthesis and water evaporation. To perform these functions most effectively, the sheet must have the shape of a plate, that is, it must have a large surface and be thin. These are the leaves of most plants. However, in some plants, the leaves in the process of evolution have changed (underwent changes) and became unlike ordinary leaves. The reason for this phenomenon is that the leaves have begun to perform other functions unrelated to photosynthesis and evaporation. The leaves of a number of plants in arid habitats have evolved into thorns. Such leaves, on the one hand, almost do not evaporate water, on the other hand, they protect plants from being eaten by animals. Examples of plants in desert areas with thorns are various cacti. Their photosynthesis takes place in the cells of the thick stem located closer to the surface. Also, water is stored in the stem. Thus, the leaves modified into thorns lost both of their main functions (photosynthesis and evaporation), but instead began to perform a protective function. Cactus Thorn leaves can be observed not only in desert and semi-desert plants. Barberry, rose bushes, rose hips, etc. have thorns. However, in these plants, not all leaves are modified into thorns, but only some. At the same time, the function of thorns here is the same as that of cacti - protection from being eaten by animals. Rosehip branch The photo shows thorns - modified rosehip leaves. The leaves of other plants in arid habitats have adapted to the lack of moisture in a different way. So in aloe and agave, the leaves have changed into thick and juicy formations in which water is stored. And in order to reduce evaporation, such leaves are covered with a waxy coating, hairs, and have fewer stomata. In this case, the leaves have changed so that they have not lost their main functions, while acquiring an additional one - water storage. Aloe There are plants in which the leaves are modified into tendrils. With these antennae, the plant clings to the support and is held in an upright position. Examples of tendril plants are peas, rank, vetch, and other legumes. In peas, the upper parts of the leaves are turned into antennae. Pea antennae In nature, there are insectivorous plants. Their leaves have been modified into a kind of trapping apparatus. When an insect sits on a leaf of a sundew plant, it sticks to it, since the leaf is covered with hairs that emit a viscous mass. After that, the hairs and the sheet itself are curled up. Inside the formed cavity, the insect is digested due to the enzymes secreted by the leaf. From the insect, the sundew assimilates nitrogen-rich organic substances. It is because of the lack of nitrogen and other trace elements in their habitats that the sundew leaves acquired such a specific function. Rosyanka Another modification of the leaves is the scales. In this case, the scales are different, since they perform different functions. For example, in an onion in a bulb, the leaves are turned into juicy scales, in which a supply of nutrients is deposited. Other scales cover the kidneys. In this case, they perform a protective function.

The leaf is one of the most flexible plant organs. In the process of adaptation to environmental conditions, the whole leaf or part of it may change the main function. This leads to qualitative changes in the external appearance and internal structure of the leaf, that is, there are modifications or metamorphoses of the leaf (Fig. 32).

Thorns

This modification is characteristic of plants living in dry and hot climates, although they often occur in plants of other climatic zones. The thorns reduce transpiration and protect the plants from being eaten by animals.

The metamorphosis of the entire leaf into a thorn is characteristic of cacti. In many astragalus, sainfoin, the rachis of a complex leaf turns into a thorn, in the white acacia - stipules.

These are thread-like formations that are sensitive to touch and are adapted for climbing. In vetch, lentils, peas, the upper part of the rachis and several upper leaves are transformed into a tendril. In the leafless rank, all the leaves are reduced, and the rachis is the only antenna (the function of photosynthesis is taken over by the stipules.

Fishing apparatus

They are found in plants growing on swampy, peaty, poor in minerals soils. With the help of trapping devices, the sundew in middle lane, Venus flytrap in North America, Nepentes in tropical Asia use nitrogen and phosphorus rich organic food to digest animals. The structure of the trapping apparatus is different (nepentes jugs, venus flytrap traps, sundew leaves), but they are all capable of capturing and digesting insects and other small animals with the help of enzymes secreted by special digestive glands.

Rice. 32. Modifications of the sheet:

1 - tendril of a leafless rank; 2 - thorn of milkweed brilliant; 3 - the trapping apparatus of nepentes.

Leaf fall

When leaves reach their maximum size, aging processes begin in them, leading to the death of the leaf. With aging, the intensity of photosynthesis and respiration in the leaves decreases, and the content of protein nitrogen and RNA in tissues decreases. Decay processes, rather than synthesis, begin to prevail. Organic matter flows out of old leaf tissues. At the same time, some salts, such as calcium oxalate crystals, accumulate in the leaves.

A sure sign of leaf aging is discoloration. Leaves lose their green color as a result of chloroplast degradation. The yellowing and reddening of the leaves is associated with the accumulation of carotenoids and anthocyanins in them.

In monocotyledonous and herbaceous dicotyledons, the leaves gradually die off and are destroyed, remaining on the stems. By trees and shrubs

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Rice. 33. Formation of a separating layer:

1 - wood; 2 - core; 3 - bast; 4 - periderm; 5 - a separating layer; 6 - conducting bundle; 7 - leaf petiole.

truths fall. Massive leaf fall is called leaf fall... Falling leaves are caused by changes in the leaf, namely at the point of attachment of the leaf to the stem. At the base of the petiole in the transverse direction, a special separating layer is formed, consisting of an easily exfoliating parenchyma (Fig. 33). From the side of the stem, the cells closest to the base of the petiole become corky and form a protective layer that remains after the leaf falls in the form of a leaf scar. For some time, the leaf is held by the veins. But under the influence of the gravity of the leaf and gusts of wind, they burst, and the leaves fall off.

Leaf fall is an important plant adaptation to reduce moisture evaporation. It also protects plants from mechanical damage in winter.

Modifications of leaves Functions of modified leaves Example of a plant Thin scales Protection Onion Juicy scales Storing nutrients Onions Thorns Reducing moisture evaporation, protecting against eating by animals Cactus, camel thorns, barberry Antennae Anchoring the climbing stem Peas, vetch, rank Insectivorous plants Insect trapping and digestion (nitrogen) Sundew, flyfoot, venice

This is interesting: * The cypress has the largest number of leaves on the shoots, million scaly leaves. A large oak tree grows on average about 250 thousand leaves.

* In the 80s of the twentieth century, competitions of insectivorous plants were held in France. First place went to Emile Marcier. His sundew caught 51 mosquitoes in 3 hours. * The folding of the trapping leaves of the Venus flytrap when it hits the leaf of an insect occurs instantly - in just 0.02-0.05 seconds, and so reliably that the trap leaf cannot be opened without damaging it. * Royal Dewdrop, native to South Africa, is capable of digesting snails and frogs.

1. The leaf, being part of the shoot, in turn consists of: a) a plate c) stipules b) a petiole and a base d) everything is correct 2. A complex leaf consists of: a) one leaf blade and one petiole b) one leaf blade and several petioles c) several leaf blades and one petiole d) several leaf blades and several petioles 3. The function of the leaf skin is: a) protection of the inner tissues of the leaf b) carrying nutrients c) formation organic matter d) everything is correct Choose the correct answer:

4. Pea antennae are modified: a) stipules c) lateral shoots b) leaves of a complex leaf d) everything is correct 5. Any simple leaf has: a) leaf blade and base b) leaf blade, base and petiole c) leaf blade and petiole d) everything is correct 6. Cactus spines are: a) modified shoots b) special outgrowths of stem skin cells c) modified leaves d) everything is correct

7. Have aquatic plants, for example, in a water lily, the stomata are located: a) on the upper side of the leaf b) on the edges of the leaf protruding above the water c) on the lower side of the leaf d) everything is correct 8. Sessile leaves do not have: a) leaf blade c) petiole b) conductive tissues d) base of the leaf 9. Functions of the leaf: a) evaporation c) photosynthesis b) gas exchange d) everything is correct 10. Onion leaves: a) protect the plant from animals b) raise shoots closer to the light c) store up nutrients d) everything is correct