Cactus is one of the most amazing plants that can survive in the most arid regions of the Earth. The homeland of cacti is called South and part of North America.

The structure helps these plants survive in conditions of severe water shortage. Most cacti have a fairly thick main stem that stores a strategic supply of water.

The cactus has another feature - very long roots. But the most amazing thing about cacti is their spines, which cover the stem of the plant and are a kind of modification of the leaves, the presence of which is characteristic of all plants. Cacti abandoned the leaves, as they will simply evaporate the moisture that is so necessary in the growing conditions of the cactus.

But how does a cactus do without leaves? Their function was partially taken over by the stem, which is equipped with stomata. They are in a closed state and absorb the necessary carbon dioxide. Without carbon dioxide, the vital process of photosynthesis is impossible for plants.

In addition to protecting against excessive evaporation of moisture, thorns, on the contrary, help the cactus to obtain much-needed water. The initial function of extracting moisture is provided by the roots of the cactus. They are very long, but located in the upper layers of the soil. Due to them, the cactus covers a large area of ​​\u200b\u200bthe soil and can absorb as much moisture as possible.

But only rains in arid regions are extremely rare and sometimes do not soak the soil to the required depth. In such a situation, the cactus, having no spines, would simply die. The thing is that thorns have a unique ability to attract tiny droplets of water electrostatically. It doesn't have to wait for rain. Temperature fluctuations in those places where cacti grow are quite high, so abundant dew forms in the air, which is the main source of life-giving moisture.

The cactus took care of its safety by acquiring thorns. Since it stores a large supply of water, which is especially scarce in deserts, many animals are not averse to eating such a juicy fruit. And then large thorns become to protect the plant, with which no animal can cope.

Also, the spines help the cactus in the process of pollination. They secrete a special nectar that attracts pollinating insects. This ensures the process of reproduction of cacti.

If the cactus grows in a fairly mild climate zone, where there is enough moisture, then the spines on it are quite rare and very long. In this case, they are assigned only a protective function. The more moisture a cactus needs, the more spines it will have on its trunk.

Numerous plants have thorns, but in cacti the thorns are bundled. Biologists have concluded that spines are analogous to leaves or bud scales. However, these changes are quite significant. Mature spines do not contain the same types of cells or tissues that are found in tree leaves. The spines consist only of heart-shaped fibers surrounded by an epidermis. They have neither stomata nor guard cells.

honey glands

In several species of cacti, the spines in each axillary embryo develop as secretion glands. They are known as "honey glands". These formations secrete, which attracts ants. The spikes in such places consist of loosely arranged parenchyma cells that protrude into the intercellular space. The accumulated nectar is pushed up through small holes in the epidermis. The spines of this type are short and wide. They are made up of thin-walled fibres. The smell also helps attract flying insects that pollinate the cacti.

Protective spikes

Many cacti are protected from hot sunlight by a dense covering of thorns. Surprising is the fact that more than half of all types of cacti are adapted to living in dark forests or cool and humid highlands. Such plants will be quickly dried by exposure to sunlight in the desert.

The appearance of cacti that live in cool or shady places is often very different from the rest. They have either only a few long spines or many very short ones. Plants growing in sunny and hot deserts should be completely covered with thorns. The injections from such thorns are very strong and painful. Many species of cacti have thorns so soft that animals can eat them without any problems.

The benefit of a thorn cover is to block sunlight, prevent overheating of the plant, reduce chlorophyll evaporation, and protect against damage. For example, in Mammillaria Plumosa, epidermal cells grow outward as long trichomes, giving the plant an unusual appearance. In other species, the spines are flat, thin and long. On the one hand, this makes them too flexible and deprives the plant of protection. On the other hand, they are quite wide and give the plant shade. Such spines help the cactus to hide among the grass in which it grows.

The main functions of leaves are photosynthesis and water evaporation. In order to perform these functions most effectively, the sheet must be in the form 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 (have undergone changes) and become unlike ordinary leaves. The reason for this phenomenon is that the leaves began to perform other functions not related to photosynthesis and evaporation.

The leaves of a number of plants in arid habitats have evolved into spines. Such leaves, on the one hand, almost do not evaporate water, on the other hand, protect plants from being eaten by animals. An example of plants of desert places with thorns are various cacti. Their photosynthesis proceeds in the cells of the thick stem located closer to the surface. The stem also stores water. Thus, the leaves modified into spines lost both of their main functions (photosynthesis and evaporation), but instead began to perform a protective function.

Spiny leaves can be observed not only in plants of deserts and semi-deserts. Barberry, rose bushes, wild rose, etc. have spines. However, in these plants, not all leaves are modified into spines, but only some. At the same time, the function of the spines here is the same as that of cacti - protection from being eaten by animals.

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 to reduce evaporation, such leaves are covered with a wax 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 - storing water.

There are plants whose leaves are modified to antennae. With these tendrils, the plant clings to the support and is held in an upright position. An example of plants with tendrils are peas, chin, vetch and other legumes. In peas, the upper parts of the leaves are turned into antennae.

In nature, there are insectivorous plants. Their leaves are modified into peculiar trapping devices. When an insect sits on a leaf of a sundew plant, it sticks to it, because the leaf is covered with hairs that secrete a viscous mass. After that, the hairs and the leaf itself are folded. Inside the resulting cavity, the insect is digested due to the enzymes secreted by the leaf. Sundew assimilates nitrogen-rich organic matter from the insect. It is precisely because of the lack of nitrogen and other trace elements in their habitats that sundew leaves have acquired such a specific function.

Another modification of the leaves are scales. In this case, the scales are different, because they perform various 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.

* This work is not a scientific work, is not a final qualifying work and is the result of processing, structuring and formatting the collected information, intended to be used as a source of material for self-preparation of educational work.

Cacti are perennial succulents of the cactus family. Mostly inhabitants of deserts and semi-deserts of the American continent.

The leaves of cacti are reduced and replaced by spines in most species, the stems are capacious water reservoirs. All cacti have areoles (axillary bud metamorphosis), from which flowers develop, "children" of cacti grow. A peculiar appearance, combined with a very beautiful flowering, has made these plants very popular among lovers of indoor floriculture. The following species and groups of species are recommended for room culture.

Peyrescias have true leaves and grow into large shrubs, often serving as rootstocks for grafting cacti with weak roots onto them.

Prickly pear are characterized by flattened articulations of the stem and areoles, on which, in addition to spines, very sharp small bristles (glochidia) develop, which easily pierce skin and clothing. However, they are often very decorative (for example, in varieties of finely pubescent prickly pear).

Cereus are distinguished by columnar faceted stems, in different species originally pubescent with long or short hairs, or naked and bluish (cereus, cephalocereus, espostoa, oreocereus, lemereocereus, trichocereus).

The group of "blackberry" cacti covers a wide variety of genera, which are characterized by a rounded shape and many spines (hence the name). For breeding in rooms, we can recommend Echinopsis, Echinocactus, Echinocereus, Rebutia, Ailostera, Lobivia and Pseudo-Lobivia, parody, hymnocalycium, ferocactus, hamatocactus and many others.

Mammillaria - a group of papillary cacti; differ in a variety of shapes and spines. In Mammillaria, the tubercles (papillae) are arranged in a spiral around the stem, and the flowers arise between the areoles on the tubercles.

Unlike the above species, epiphyllum, ripsalis, epiphyllopsis, ripsalidopsis and zygocactus are forest cacti. Most of them are epiphytes, so in room culture they develop better when grafted (for example, on Peiresia). These are shade-loving plants, they do not tolerate direct sunlight. In winter, they require constant moisture. They should be planted in loose humus soil with an admixture of sand and coal.

All desert cacti can be cultivated in soil composed of soddy and leafy soil with the addition of river sand, broken bricks or shards, chalk and charcoal. These are light-loving plants, they need the maximum amount of sun and grow very well outdoors. In winter, cacti should be kept in a cold (from -6 degrees to -8 degrees) and always dry place. From October to March, cold wintering cacti should not be watered, then they bloom intensively. The best way to water is to submerge the plant pots in water until air bubbles stop, and then dry them well. The bottom of the pot must be covered by 3-4 cm with a layer of small shards. In young plants, the need for moisture is higher, so in winter they need to be watered once a month and ensure that the earth does not dry out and does not turn into dust. It is difficult to dry adult cacti, and they easily rot from excess water. Reducing watering in winter does not yet give the cactus the desired dormant period.

This requires a lower temperature, which is easy to achieve by fencing off the window sill with cacti on it from the room with glass or plastic wrap.

Sowing cacti requires special attention. It is necessary to sow the seeds in washed river sand, mixed in half with leafy soil, slightly pressing the seeds. Before the emergence of seedlings, it is advisable to keep the crops at a temperature of 25-30 degrees and spray only from a spray bottle. At first, crops should be covered with glass. Small shoots should be dived several times so that they develop better. In the first year, they should not be dried out, kept in too bright sun or in drafts.

It is easier to propagate cacti from cuttings. Cuttings should be cut with a sharp knife, sprinkled with sulfur or coal and left to dry for 3-4 days. Cuttings should be rooted in washed river sand (preferably heated). As soon as the roots are formed, and the cuttings begin to grow noticeably, they can be planted in a small dish. 3-5 days before transplanting, watering the cacti should be stopped so that the earth ball dries up and the earth easily separates from the roots. After transplantation, the plant must be placed in the shade and not watered for 5 days, so that the roots accidentally injured during transplantation do not rot. The best time to transplant is spring. In order not to prick your hands, cacti during transplantation should be kept with a strip of sufficiently dense paper folded several times.

Cactus adaptations to environmental conditions.

Spreading. The homeland of cacti is continental and island America. They are found from Canada to Patagonia and Tierra del Fuego and from the Galapagos Islands to the West Indies. Mexico is richest in species and life forms of cacti. In the USA, cacti are especially numerous in Texas, Arizona and New Mexico, although the natural range of the family covers almost all states, with the exception of Hawaii, where cacti have become naturalized after the introduction. Thinly branched epiphytic cactus Rhipsalis grows wild in western Africa, Madagascar and Sri Lanka.

Chemistry, Biology, preparation for the GIA and the Unified State Examination

It is believed that it was brought there in ancient times by birds or humans.
Origin: The ancestors of cacti were, most likely, rather moisture-loving plants with well-developed leaves, possibly lianas. As a result of geological processes, the climate in the places of growth of ancient cacti has become much drier. Plants that failed to adapt to the changed conditions died out, and cacti survived due to partial or complete reduction of leaves.
Adaptations.

The cactus tries to absorb as much moisture as possible and store it for a long time. And then very slowly consumes it. So, the cactus must increase its volume in order to store more water, but must decrease its surface area in order to reduce evaporation. From mathematics it is known that the geometric body that has the largest volume with the smallest surface is a ball. Therefore, cacti are most often found spherical.

The function of the leaves is performed by a green stem of a round, squat or elongated cylindrical shape, ribbed, flat like a leaf or elongated like a vine. They took over the main function of the leaves - photosynthesis.

The giant carnegia cactus lives 150-200 years, sometimes reaching a weight of 7 tons. Widespread root system is located at the very surface of the soil. This is probably why there are no other cacti within a radius of 15-20 m. The resistance of carnegia to adverse environmental conditions is amazing: for more than a year, for example, it can be without water, and lateral shoots continue to bloom even after the death of the main trunk. The trunk of the carnegia is quite dense, and some species of woodpeckers gouge hollows in it, in which other species of birds can nest in the future.

Organisms adapt to the same environment often in different ways. General and different adaptations of shark and dolphin.

Output: adaptations of organisms appear as a result of the action of the driving forces of evolution (struggle for existence, natural selection, hereditary variability). So the natural selection of their entire variety of non-directional hereditary changes selects and fixes only those that provide the population or species as a whole with optimal adaptations to given conditions of existence .

The relative nature of fitness.

The adaptability of organisms to the environment has been developed in the process of long historical development under the influence of natural causes and is not absolute, but relative, since environmental conditions often change faster than adaptations are formed. Corresponding to a specific habitat, adaptations lose their meaning when it changes. Evidence of the relative nature of fitness may be the following facts: protective devices from some enemies are not effective from others (for example, poisonous snakes that are dangerous for many animals are eaten by mongooses, hedgehogs, pigs); the manifestation of instincts in animals may turn out to be impractical (moths collect nectar from light flowers, clearly visible at night, but they also fly to the fire, although they die at the same time); an organ that is useful in some conditions becomes useless and even relatively harmful in another environment (the membranes between the fingers of mountain geese, which never sink into the water); better adaptations to a given environment are also possible.

Adaptation to the environment is relative, useful only in the conditions in which it was historically formed. When these conditions change, adaptations lose their value or even harm the body.

Where do cacti grow?

Cacti, or simply cacti, are perennial flowering plants. It is generally accepted that they evolved about 40 million years ago. Then Africa and South America were already separated from each other, and North America had not yet joined South.

Despite the fact that no fossil remains of cacti of those times were found, it is believed that they first appeared in South America, and only 5-10 million years ago came to the northern continent.

Where do cacti grow in nature?

To this day, cacti in the wild grow mainly on the American continents. It was from there that they were once transported by people and carried by birds to Europe.

However, representatives of cacti in nature can be found not only in America. Some species have been growing for a long time in the tropical part of Africa, in Ceylon and other islands of the Indian Ocean.

Where else do cacti grow: thickets of this plant can be found in Australia, the Arabian Peninsula, the Mediterranean, the Canary Islands, Monaco and Spain. Cacti grow wild in the territory of the former Soviet Union. In most cases, cacti in these places were artificially brought by man.

Conditions for the growth of cacti

Basically, cacti prefer steppes, deserts and semi-deserts. Sometimes they can be found in tropical rainforests. Quite rare, but they still grow on wet coasts.

In Mexico, cacti grow in sagebrush, creosote, and also in high-altitude succulent deserts. In the high deserts, cacti are concentrated mainly on the Mexican plateau, as well as in the western and eastern parts of the Sierra Madre.

In what deserts cacti grow: cacti quite extensively and densely inhabit the deserts of Peru, Chile, Bolivia and Argentina. There is a rich diversity of these plants.

In which countries do cacti grow?

If we indicate the geography of cactus growth by country, the list will be approximately as follows: Mexico, Brazil, Bolivia, Chile, Argentina, USA (Texas, Arizona, New Mexico), Canada, China, India, Australia, Spain, Monaco, Madagascar, Sri- Lanka, West Africa.

As ornamental plants, people have learned to grow cacti in the open field almost everywhere, with the exception, perhaps, of the Arctic. As indoor plants, cacti have long populated the entire planet.

According to legend, one day the rose celebrated its birthday. Various plants were invited to the festival, among which there was also a cactus. The prickly friend did not have a gift, so he gave the rose his needles. And the rose, in turn, thanked the cactus with a beautiful bud that blooms once a year, on his birthday.

What are thorns

In most sources, you can find the theory that cactus spines are modified leaves. Chlorophyll, which is found inside spines at a certain stage of their development, serves as evidence. But still, it is more correct to assume that the spines are modified kidney scales.

When talking about, most people imagine something prickly and sharp. Meanwhile, in nature there is a variety of species of this plant that you can find specimens with spines in the form of wire, hair, feathers, soft bristles and paper ribbons.

What are thorns for?

The spines are a means of survival for the cactus. First, they have a protective function. Large sharp needles scare away herbivores. Spines in the form of thin and short hairs dig into the skin for a long time, repelling any desire to touch the plant again. However, the protection of spines is reduced not only to. For example, the cactus Mammillaria plumosa is covered with white feathers. He does not need protection, so high in the mountains. Feathers protect the plant from overheating, forming a kind of umbrella over it. And on cold nights, they serve as a fur coat for a cactus.

In particularly dry areas, where rains have to wait for several months, the thorns serve as a moisture storage. They are able to absorb water from the air, holding inside. Experience confirms this: if you remove the cactus from the soil and place it on a dry napkin, the plant will continue to grow, consuming internal moisture reserves. Static electricity attracts the smallest particles of water that are contained in the morning mist or dew. At the end of the thorn, a drop of water is formed, which is absorbed by the plant. If the “storage” in the needle is full, water flows in thin streams along the stem to the roots of the cactus.

Some types of cacti continue their genus with the help of thorns. For example, Cylindoropuntia has many processes covered with tenacious spines. With them, the plant clings to the wool of approaching animals, which, in turn, carry the shoots to other areas. There are also species in which the "hooks" are located on the seeds and fruits. And there are specimens that have nectar-bearing spines. This is how the plant attracts pollinators.

24.09.2014

The birthplace of cacti is considered to be South America and part of North. Evolutionarily, cacti as representatives of the world of flora appeared approximately 40 million years ago. They belong to the succulent plant family. Thorns appeared not as a decorative element, but with meaning. They have evolved over many centuries and have become a real survival organ.

In the main thick stem of the cactus, a strategic supply of nutrient moisture is concentrated. Another feature of the cactus is the incredibly long roots that go underground and occupy an impressive surface radius in their habitat. Therefore, they can collect life-giving moisture over a fairly large area. Do not think that cacti do not tend to have leaves, like all plants known to us. It's just that the function of the leaves is performed by these very spines - a modified version of the leaves. At the heart of spines is a material similar to organic matter - chitin.

Cacti abandoned the leaves of the form we are used to for a completely objective reason. As a rule, cacti grow in arid places, and wide leaves would become completely irrational and evaporate precious water in large quantities. In part, the functions of the leaves were taken over by a thick, fleshy trunk. On its surface there are very thin stomata, which, if necessary, open their pores and absorb the carbon dioxide necessary for photosynthesis.

Another unique feature of spines is that they electrostatically attract small water droplets to themselves. Therefore, rain is not always needed for the cactus to get drunk. In the climate where cacti exist, the temperature fluctuates quite a lot. Dew is steadily formed in the air, which is a constant source of moisture for cacti.

In addition to the role of water getters, thorns also perform a defensive function. Few of the animal and plant kingdoms have adapted so successfully to survive in the desert dunes, and many animals would love to eat such a succulent plant. And it is here that thorns come to the defense, with which no animal can cope. Thanks to the spines, cacti are able to be reproductive. The spines secrete nectar that attracts insects, which act as pollinators.

It is curious that the length of the spines depends on climatic conditions. The milder the climate, the rarer the spines. But they are quite long, because. they have only a protective function. The drier the climate, the correspondingly more spines on the trunk of the cactus. The spines contain a large amount of mineral salts and calcium carbonate. So, in order for the spines to grow in the soil, there must be a sufficient amount of calcium. That is why it is necessary to pour old plaster or marble chips into the ground for growing cacti.