400 million years ago, a huge part of the earth's surface of our planet was occupied by seas and oceans. The first living organisms arose in an aquatic environment. They were particles of mucus. After several million years, these primitive microorganisms developed a green color. By appearance they began to look like algae.
Plants during the Carboniferous period
Climatic conditions favorably affected the growth and reproduction of algae. Over time, the surface of the earth and the bottom of the oceans have undergone changes. New continents arose, while old ones disappeared under water. The earth's crust was actively changing. These processes led to the appearance of water on the earth's surface.
Retreating, sea water fell into crevices and depressions. They then dried up, then filled with water again. As a result, those algae that were on seabed, gradually moved to the earth's surface. But since the drying process occurred very slowly, during this time they adapted to the new living conditions on earth. This process took place over a million years.
The climate at that time was very humid and warm. It facilitated the transition of plants from marine to terrestrial life. Evolution led to a more complex structure various plants, ancient algae also changed. They gave rise to the development of new earthly plants - psilophytes. In appearance, they resembled small plants that were located near the banks of lakes and rivers. They had a stem that was covered with small bristles. But, like algae, psilophytes did not have a root system.
Plants in a new climate
Ferns evolved from psilophytes. The psilophytes themselves ceased to exist 300 million years ago.
Humid climate and a large number of waters led to the rapid spread of various plants - ferns, horsetails, mosses. The end of the Carboniferous period was marked by a change in climate: it became drier and colder. Huge ferns began to die out. The remains of dead plants rotted and turned into coal, which people then used to heat their homes.
Ferns had seeds on their leaves, which were called gymnosperms. From giant ferns came modern pines, spruces, and firs, which are called gymnosperms.
With climate change, ancient ferns have disappeared. The cold climate destroyed their tender sprouts. They were replaced by seed ferns, which are called the first gymnosperms. These plants have adapted perfectly to the new conditions of a dry and cold climate. In this plant species, the reproduction process did not depend on water in the external environment.
130 million years ago, various shrubs and herbs arose on Earth, the seeds of which were located in the surface of the fruit. They were called angiosperms. Angiosperms have lived on our planet for 60 million years. These plants have remained virtually unchanged from then to the present day.
400 million years ago, a huge part of the earth's surface of our planet was occupied by seas and oceans. The first living organisms arose in an aquatic environment. They were particles of mucus. After several million years, these primitive microorganisms developed a green color. In appearance they began to resemble algae.
Climatic conditions favorably affected the growth and reproduction of algae.
Over time, the surface of the earth and the bottom of the oceans have undergone changes. New continents arose, while old ones disappeared under water. The earth's crust was actively changing. These processes led to the appearance of water on the earth's surface.
Retreating, sea water fell into crevices and depressions. They then dried up, then filled with water again. As a result, those algae that were on the seabed gradually moved to the earth's surface. But since the drying process occurred very slowly, during this time they adapted to the new living conditions on earth. This process took place over a million years.
The climate at that time was very humid and warm. It facilitated the transition of plants from marine to terrestrial life. Evolution led to a more complex structure of various plants, and ancient algae also changed. They gave rise to the development of new earthly plants - psilophytes. In appearance, they resembled small plants that were located near the banks of lakes and rivers. They had a stem that was covered with small bristles. But, like algae, psilophytes did not have a root system.
Plants in a new climate
Ferns evolved from psilophytes. The psilophytes themselves ceased to exist 300 million years ago.
The humid climate and large amounts of water led to the rapid spread of various plants - ferns, horsetails, mosses. The end of the Carboniferous period was marked by a change in climate: it became drier and colder. Huge ferns began to die out. The remains of dead plants rotted and turned into coal, which people then used to heat their homes.
Ferns had seeds on their leaves, which were called gymnosperms. From giant ferns came modern pines, spruces, and firs, which are called gymnosperms.
With climate change, ancient ferns have disappeared.
The cold climate destroyed their tender sprouts. They were replaced by seed ferns, which are called the first gymnosperms. These plants have adapted perfectly to the new conditions of a dry and cold climate. In this plant species, the reproduction process did not depend on water in the external environment.
130 million years ago, various shrubs and herbs arose on Earth, the seeds of which were located in the surface of the fruit. They were called angiosperms. Angiosperms have lived on our planet for 60 million years. These plants have remained virtually unchanged from then to the present day.
Without plants, our planet would be a lifeless desert. And tree leaves are small factories or chemical laboratories, where, under the influence sunlight and heat, the transformation of substances occurs. Trees not only improve the composition of the air and soften its temperature. Forests have medicinal value and provide most of our food needs, as well as materials such as wood and cotton; They are also raw materials for the production of medicines.
I. What were the very first plants on earth?
Life on Earth began in the sea. And plants were the first to appear on our planet. Many of them made it to land and became completely different. But those that remained at sea remained almost unchanged. They are the most ancient, it all began with them. Without plants, life on Earth would not be possible. Only plants are able to absorb carbon dioxide and release oxygen. To do this they use the sun's rays. One of the first plants on earth were algae.
More than 20,000 species of algae are known. They can be anchored to rocks or the seabed using a foot-like “brace” that extends into a branch with leaves. Brown algae grows in cold waters and reaches enormous sizes. Red algae are characteristic of warm seas. Green and blue-green algae can be found in both warm and cold waters. Brown algae produces a lot of useful substances, used in the production of plastics, varnishes, paints, paper and even explosives. They are used to make medicine, fertilizer, and feed for livestock. Among the peoples of Southeast Asia, seaweed is the basis of many dishes.
Algae "Floating Forest".
In the old days there were legends about the Sargasso Sea, where ships died after getting stuck in algae. But still, in some places the algae thickets are so thick that they can hold up a light boat. This is the brown algae called sargassum, after which the sea itself is named. Sargassum looks like bushes dotted with “berries” - air bubbles that allow the plant to float on the surface of the water. Unlike other large algae, sargassum does not attach to the bottom and travels along the waves in huge clusters, forming a floating forest. A myriad of mollusks, worms, and bryozoans attach to the leaves of Sargassum; crabs, shrimp, and fish hide in its thickets. Almost all of the “residents” are brownish-yellow in color, similar to sargassum, and their bodies often copy the shapes of the “leaves” of this algae. Some hide so as not to scare off their prey. So this whole community floats, never touching the shore.
II. They feed, clothe, make you happy.
1. Trees that provide food.
Coffee is one of the most popular drinks in the world.
Who gave us this wonderful drink and how? If you believe the ancient Arab legend, then we owe the discovery of coffee. goats. One Ethiopian shepherd, according to legend, noticed that his goats, having eaten some berries from a bush, continued to graze all night, without thinking of resting. The shepherd told the wise old man about this, and he, having tasted these berries, discovered their wonderful power and invented the drink coffee.
The Ethiopians liked coffee so much that later one of the tribes, having moved to the Arabian Peninsula, took its grains with them. This was the beginning of the first coffee plantations. And this happened, as is known from ancient manuscripts, in the 9th century. Coffee was known only to the Arabs for quite a long time, but the Turks, who conquered it in the 15th-16th centuries. part of the Arab territories also appreciated the taste and wonderful properties of the drink. This is how the famous method of making Turkish coffee appeared: coffee is brewed on hot sand in special copper vessels with a handle - “Turks”.
Europeans were first introduced to coffee by an Italian who returned from Turkey. A doctor by profession, he recommended his patients to drink coffee for medicinal purposes. Venice was the first to import coffee to Europe. And in 1652 the first coffee shop was opened in England. Turkey was the monopoly supplier of coffee to Europe, but the cunning Dutch, having stolen seedlings of coffee trees from the Turks, transported them to Indonesia, where the climate was quite suitable for growing coffee.
Brazil is now the world leader in coffee production.
Coffee came to Russia thanks to Peter I.
Coffee drink is brewed from processed seeds coffee tree. This evergreen from the madder family. The white lush inflorescences of the coffee tree, located in the axils of the leaves, after pollination by insects turn into fruits - the red berries are removed from them, the seeds are polished in special drums and packed in bags. Before brewing coffee beans fried.
The birthplace of coffee is Africa. The Arabian variety is considered the highest quality and tastiest. Brazilian coffee (this is not a type, but only a place where coffee is grown), which fills all markets in the world, is much worse in quality than coffee grown in other countries.
2. Noble friends.
Cedrus are real cedars. Phenicia, Egypt, Assyria were powerful powers of antiquity. But they occupied deserted territories; there were almost no forests there. And wood is needed both for the construction of housing and for ships. The wood is strong and rot-resistant. The cedar that the ancients loved is not the cedar that grows in the taiga and is famous for its delicious nuts. Siberian pines are the namesakes of real cedars - cedrus trees.
The Phoenicians cut Cedrus for ships, the Egyptians for sarcophagi for the funeral ceremonies of their nobles, the Greeks and Romans used cedar for building temples and making furniture. Later, the crusaders began cutting down the cedrus trees. And during the First World War, the most valuable cedars with their pink wood, for lack of other fuel, were burned in locomotive furnaces. There are only 4 groves of Lebanese cedars left. True, other types of cedrus - Atlas, Cypriot and Himalayan - although very rare trees, unlike the Lebanese cedar, they are not endangered.
Lebanese cedars are majestic trees with horizontal, powerful branches. Their needles are bluish, collected in tassels. The cones are the size of a fist, dense, almost smooth, like barrels. When the seeds in them ripen, the cones do not open, but crumble, and the ground is covered with a layer of scales. The wind blows the winged seeds off them and spreads them around. If the goats, which local residents raise in abundance, do not eat the young shoots, they may grow into a new generation of beautiful cedars. The fame of the beauty of Lebanese cedars also reached Russia. Therefore, when Russian pioneers saw Siberian pines, tall, majestic, with large cones, they called them cedars.
Siberian cedar is an amazing pine. The main wealth of cedar is its nuts. They contain fats, proteins, starch, vitamins B and D, and the needles contain many healing substances. Nuts contain more than 60% oil, which is superior in many qualities to animal fats and is not inferior in nutritional value to meat and eggs. Under Ivan the Terrible, these nuts were exported abroad, and under Peter I, they began to be used in Russia to prepare a healing and strengthening remedy - nut milk.
Pine nuts play a huge role in the lives of animals. “Where there is no cedar,” the hunters say, “there is no sable.” The nuts are eaten by bears and chipmunks, squirrels and various birds.
Cedar resin is also healing. During the Great Patriotic War Cedar balsam helped with wounds and burns. Resin is a necessary raw material for obtaining such a valuable medicine as camphor. Resin is also needed in optical technology.
Cedar wood is also valuable - pencil sticks are made from it, musical instruments, make furniture. Turpentine and other useful products are obtained from sawdust.
III. Study of tree bark.
Norway maple
The maple tree I was watching is young. It has a tree trunk, which thickens every year, and side branches extend from it to form a crown, which consists of smaller branches and leaves. The tree is held in the soil by its roots, which absorb moisture and dissolved minerals. Therefore, the tree trunk is wider at the bottom.
If you smell the bark, the smell is bitter and astringent. In spring, the smell of the bark intensifies and becomes sweetish.
There is no hollow in my tree. But I have met trees with hollows. Various birds make their homes in the hollow.
There are no lichens, mosses or mushrooms on the maple tree that I am observing. Sometimes mushrooms form fungal roots on the roots, supplying the trees with nitrogen and minerals.
On the bark of my tree there are traces left by man: peeled bark and scratches from a knife, which over time it could heal.
IV. Why is my friend the best?
Norway maple – branch with fruits
Maple is one of the most elegant trees growing in our forests. In the spring, when the tree branches are not yet covered with leaves, the maple blooms. Its yellow-green flowers, collected in an inflorescence, are pleasing to the eye. The maple tree is no less elegant in the summer, when its crown becomes “curly.” The autumn outfit is not inferior in beauty to any other plant. The tree seems to be on fire, striking in its richness of shades of crimson and green, orange and yellow. Each leaf has its own color, and each leaf is beautiful in its own way. And they all have the same shape: round with 5-7 sharp protrusions, hence the name Norway maple. Maple is a good honey plant. Up to 10 kg of honey is obtained from one tree. Norway maple sap is very tasty. In Russia, kvass and various soft drinks were prepared from it.
The Canadian flag features a leaf from the Sugar Maple tree. Its sweet juice was used to make maple syrups, molasses, and even maple beer, which was very popular in the 19th century. Canada was the leader in the production of juice products. The maple leaf has become the national symbol of this country.
Musical instruments were made from maple wood, which was durable and light. Sports equipment is also made from maple. Pharmacists and chemists use the leaves and bark. Maple has one more interesting property: He can predict the weather. From the petioles of the leaves, right next to the branch, sometimes “tears” flow drop by drop - the maple seems to be crying. This is the property of maple to get rid of excess moisture. And the “tears” of the maple depend on whether the air is dry or humid. The drier the air, the stronger the evaporation and vice versa. The air becomes humid when rain approaches. If appeared on maple leaves“Tears mean it will rain in a few hours.
V. Fossil trees that remain on earth.
An ancient, ancient ginkgo tree! It appeared on earth back in the time of dinosaurs - 125 million years ago.
years ago. And since then this plant has hardly changed. Ginkgo is a beautiful tree up to 30 m high, with large fan-shaped leaves. The appearance of ginkgo resembles our ordinary aspen. But it was not there! Ginkgo is a gymnosperm plant, more closely related to the spruce than to the flowering plant aspen. In spring, “catkins” appear on the branches along with the foliage. By autumn, large seeds resembling plums hang on the branches. The pulp of the seed, similar to the fruit, is actually just the seed coat. It is edible and tastes salty. The only problem is that it smells like rotten meat. This is a way to attract seed dispersing animals. Ginkgo, although it survived the dinosaurs, did not survive in the wild. This tree became a garden tree. In Japan and China, it is considered sacred and is grown near temples. Now ginkgos are also appearing on the streets of European cities. Ginkgo easily resists atmospheric pollution, diseases, and insects. Ginkgo leaves and wood contain substances that repel insects. Bookmarks made from dried ginkgo leaves will protect ancient manuscripts from bookworms. And walls covered with ginkgo shingles will not allow cockroaches or bedbugs into the house.
CONCLUSION.
What can I do for all the trees?
When I come to the forest, I will not light fires.
This may lead to fires.
I won't destroy birds' nests. Birds eat insects that harm trees. I will not break branches from trees and bushes. I will plant new seedlings in the yard and take care of them in the future.
Acid rain also causes irreparable damage: destruction of crops, flora and fauna, and destruction of buildings.
First land plants
Life originated in water. The first plants, algae, appeared here. However, at some point, land appeared that had to be populated. The pioneers among animals were lobe-finned fish. And among plants?
What did the first plants look like?
Once upon a time, our planet was inhabited by plants that had only a stem. They were attached to the ground by special outgrowths - rhizoids. These were the first plants to reach land.
Scientists call them psilophytes. This is a Latin word. Translated, it means “naked plants.” Psilophytes really looked “naked.” They only had branching stems with ball-shaped outgrowths in which spores were stored. They are very similar to the “alien plants” that are depicted in illustrations for science fiction stories.
Psilophytes were the first land plants, but they lived only in swampy areas, since they did not have roots and could not obtain water and nutrients from the soil. Scientists believe that these plants once created entire huge carpets over the bare surface of the planet. There were both tiny plants and very large ones, taller than human height.
How did scientists learn about the first plants?
Scientists learned that such plants once existed on our planet only at the beginning of the last century, in 1912, thanks to a Scottish rural doctor who was interested in geology. While examining the soil, he discovered the remains of hitherto unknown plants, which were later called rhinia, after the name of the village in which it was first found. It is believed that it was the first land plant, from which other psilophytes descended.
Ancient plants dominated the planet for millions of years, but became extinct long before humans appeared. But they left their “descendants” - they became horsetails, mosses and ferns. Some scientists believe that lower psilophytes became the ancestors of modern mosses.
Question 1. When did the first ones appear? land plants?
At the beginning of the Paleozoic era, plants inhabited mainly the seas, but in the Ordovician - Silurian the first land plants - psilophytes - appeared (Fig. 1).
Rice. 1. The first land plant
These were small plants, occupying an intermediate position between algae and terrestrial vascular plants. Psilophytes already had a conducting (vascular) system, the first poorly differentiated tissues, and could strengthen in the soil, although roots (like other vegetative organs) were still absent. The further evolution of plants on land was aimed at differentiating the body into vegetative organs and tissues and improving the vascular system (ensuring the rapid rise of water to high altitudes).
Question 2. In what direction did the evolution of plants on land go?
After the appearance of psilophytes, the evolution of plants on land went in the direction of dividing the body into vegetative organs and tissues and improving the vascular system (ensuring the rapid movement of water to high altitudes). Already in the arid Devonian, horsetails, mosses, and pteridophytes were widespread. Terrestrial vegetation reached even greater development in the Carboniferous period (Carboniferous), characterized by a humid and warm climate throughout the year. Gymnosperms appear, descended from seed ferns. The transition to seed propagation gave many advantages: the embryo in the seeds is protected from favorable conditions membranes and is provided with food, has a diploid number of chromosomes. In some gymnosperms (conifers), the process of sexual reproduction is no longer associated with water. Pollination in gymnosperms is carried out by the wind, and seeds have adaptations for distribution by animals. These and other advantages contributed to the widespread distribution of seed plants. Large spore plants die out in the Permian period due to the drying climate.
Question 3. Describe the evolution of animals in the Paleozoic era.
The fauna in the Paleozoic era developed extremely rapidly and was represented by a large number of diverse forms. Life in the seas flourishes. In the Cambrian period, all the main types of animals, except chordates, already existed. Sponges, corals, echinoderms, various mollusks, huge predatory crustaceans - this is an incomplete list of the inhabitants of the Cambrian seas.
In the Ordovician, the improvement and specialization of the main types continued. For the first time, remains of animals that had an internal axial skeleton are being discovered - jawless vertebrates, the distant descendants of which are modern lampreys and hagfishes. The mouth of these peculiar organisms was a simple opening leading to the digestive tract. The anterior section of the digestive tube was pierced by gill slits, between which supporting cartilaginous gill arches were located. The jawless animals fed on organisms that lived in the muddy bottom of rivers and lakes and on detritus (organic remains), sucking food into their mouths. In some jawless animals, division of the gill arches arose, which made it possible to change the lumen of the pharynx with the help of the gill muscles and, therefore, to retain mobile prey that had entered the digestive tube.
The appearance of grasping oral apparatus- major aromorphosis - caused a restructuring of the entire organization of vertebrates.
The appearance of paired fins - limbs - is the next major aromorphosis in the evolution of vertebrates.
In the Silurian period, the first air-breathing animals - arthropods - came onto land along with psilophytes. Intensive development of lower vertebrates continued in reservoirs. It is assumed that vertebrates arose in shallow freshwater bodies of water and only then moved to the seas. The Devonian period was marked by the development of land by other arthropods - spiders; at the end of the period, the first terrestrial vertebrates appear - amphibians (stegocephals). In the Carboniferous period, reptiles (cotylosaurs), flying insects and pulmonary molluscs appeared. In the last, Permian period of the Paleozoic era, rapid development and increase in systematic groups of reptiles was observed; animal-toothed reptiles appear - the ancestors of mammals.
Question 4. What structural features of vertebrates served as prerequisites for their emergence onto land?
In the Silurian period, the first air-breathing animals - arthropods - came onto land along with psilophytes. Intensive development of lower vertebrates continued in reservoirs. It is assumed that vertebrates arose in shallow freshwater bodies of water and only then moved to the seas. In the Devonian, vertebrates are represented by three groups: lungfish, ray-finned and lobe-finned fish. It was lobe-finned fish that gave rise to the development of terrestrial vertebrates. Lobe-finned fish were typically aquatic animals, but could breathe atmospheric air using primitive lungs, which were protrusions of the intestinal wall. Only lobe-finned fish were able to adapt to life on land. Their fins were blades consisting of individual bones with muscles attached to them (Fig. 2). With the help of fins, lobe-finned fish - large animals from 1.5 to several meters in length - could crawl along the bottom. Thus, they had two main prerequisites for the transition to a terrestrial habitat: muscular limbs and lungs. At the end of the Devonian, lobe-finned fish gave rise to the first amphibians - stegocephalians.
Rice. 2. Skeleton of the paired fin of lobe-finned fish and stegocephalus:
A - shoulder girdle and fin of lobe-finned fish;
B - internal skeleton of the fin;
B - skeleton of the forelimb of stegocephalus:
1 - element corresponding to the humerus;
2 - element corresponding to the radius;
8 - element corresponding to the ulna;
4, 5, 6 - carpal bones; 7 - phalanges of fingers.
the embryonic stage of a seed plant, formed during the process of sexual reproduction and serving for dispersal. Inside the seed is an embryo consisting of a germinal root, a stalk and one or two leaves, or cotyledons. Flowering plants Based on the number of cotyledons, they are divided into dicotyledons and monocotyledons. In some species, such as orchids, the individual parts of the embryo are not differentiated and begin to form from certain cells immediately after germination.
A typical seed contains a supply of nutrients for the embryo, which will have to grow for some time without the light needed for photosynthesis. This reserve can occupy most of the seed, and sometimes is located inside the embryo itself - in its cotyledons (for example, in peas or beans); then they are large, fleshy and define general shape seed. When the seed germinates, it can be carried out of the ground on an elongating stalk and becomes the first photosynthetic leaves of the young plant. Monocots (for example, wheat and corn) have a food supply - the so-called. endosperm is always separated from the embryo. The ground endosperm of grain crops is the well-known flour.
In angiosperms, the seed develops from the ovule, a tiny thickening on the inner wall of the ovary, i.e. the bottom of the pistil, located in the center of the flower. The ovary can contain from one to several thousand ovules.
Each of them contains an egg. If, as a result of pollination, it is fertilized by a sperm that penetrates the ovary from a pollen grain, the ovule develops into a seed. It grows, and its shell becomes dense and turns into a two-layer seed coat. Its inner layer is colorless, slimy and can swell greatly, absorbing water. This will come in handy later when the growing embryo has to break through the seed coat. The outer layer can be oily, soft, filmy, tough, papery and even woody. The so-called seed coat is usually noticeable. hilum - the area by which the seed was connected to the achene, which attached it to the parent organism.
The seed is the basis for the existence of the modern plant and animal world. Without seeds, there would be no coniferous taiga, deciduous forests, flowering meadows, steppes, grain fields on the planet, there would be no birds and ants, bees and butterflies, humans and other mammals. All this appeared only after plants, in the course of evolution, arose seeds, within which life can, without declaring itself, persist for weeks, months and even for many years. The miniature plant embryo in the seed is capable of traveling long distances; he is not tied to the earth by roots, like his parents; does not require either water or oxygen; he is waiting in the wings so that, once in appropriate place and after waiting for favorable conditions, begin development, which is called seed germination.
Evolution of seeds.
For hundreds of millions of years, life on Earth managed without seeds, just as life on the two-thirds of the planet’s surface, covered with water, does without them now. Life originated in the sea, and the first plants to conquer land were still seedless, but only the appearance of seeds allowed photosynthetic organisms to completely master this new habitat.
The first land plants.
Among large organisms, the first attempt to gain a foothold on land was most likely made by marine macrophytes - algae that found themselves on sun-heated rocks at low tide. They reproduced by spores - single-celled structures that are dispersed by the parent organism and can develop into a new plant. Algae spores are surrounded by thin shells, so they do not tolerate drying out. Underwater such protection is quite sufficient. Spores there are spread by currents, and since the water temperature fluctuates relatively little, they do not need to wait a long time for conditions favorable for germination.
The first land plants also reproduced by spores, but a mandatory change of generations was already established in their life cycle. The sexual process included in it ensured the combination of hereditary characteristics of the parents, as a result of which the offspring combined the advantages of each of them, becoming larger, more resilient, and more perfect in structure. At a certain stage, such progressive evolution led to the appearance of liverworts, mosses, mosses, ferns and horsetails, which had already completely left the reservoirs on land. However, spore reproduction did not yet allow them to spread beyond swampy areas with moist and warm air.
Spore-bearing plants of the Carboniferous period.
At this stage of the Earth's development (approximately 250 million years ago), giant forms with partially lignified trunks appeared among the ferns and lycophytes. Equisetoids, whose hollow stems were covered with green bark impregnated with silica, were not inferior to them in size. Wherever plants appeared, they were followed by animals, exploring new types of habitats. In the humid twilight of the coal jungle there were many large insects (up to 30 cm in length), giant centipedes, spiders and scorpions, amphibians that looked like huge crocodiles, and salamanders. There were dragonflies with a wingspan of 74 cm and cockroaches with a length of 10 cm.
Tree ferns, mosses and horsetails had all the qualities necessary to live on land, except for one thing - they did not form seeds. Their roots effectively absorbed water and mineral salts, the vascular system of the trunks reliably distributed the substances necessary for life to all organs, and the leaves actively synthesized organic substances. Even the spores have improved and acquired a durable cellulose shell. Without fear of drying out, they were carried by the wind over considerable distances and could not germinate immediately, but after a certain period of dormancy (the so-called dormant spores). However, even the most perfect spore is a single-celled formation; In contrast to seeds, it dries out quickly and does not contain a supply of nutrients, and therefore is not able to wait long for conditions favorable for development. Yet the formation of resting spores was an important milestone on the path to seed plants.
For many millions of years, the climate on our planet remained warm and humid, but evolution in the fertile wilds of the coal swamps did not stop. In tree-like spore plants, primitive forms of true seeds first emerged. Seed ferns, lycophytes (famous representatives of the genus Lepidodendron– in Greek this name means “scaly tree”) and cordaites with solid woody trunks.
Although fossil remains of these organisms that lived hundreds of millions of years ago are scarce, it is known that tree seed ferns predate the Carboniferous period. In the spring of 1869, the Schoharie Creek River in the Catskill Mountains (New York) flooded heavily. The flood destroyed bridges, toppled trees and severely washed away the bank near the village of Gilboa. This incident would have been forgotten a long time ago if the falling water had not revealed to the observers an impressive collection of strange stumps. Their bases expanded greatly, like those of swamp trees, their diameter reached 1.2 m, and their age was 300 million years. Details of the structure of the bark were well preserved; fragments of branches and leaves were scattered nearby. Naturally, all this, including the silt from which the stumps rose, was petrified. Geologists dated the fossils to the Upper Devonian, the period before the Carboniferous, and determined that they corresponded to tree ferns. Over the next fifty years, only paleobotanists remembered the discovery, and then the village of Gilboa presented another surprise. Along with the fossilized trunks of ancient ferns, this time their branches with real seeds were discovered. These extinct trees are now classified as belonging to the genus Eospermatopteris, which translates to “dawn seed fern.” (“dawn”, since we are talking about the earliest seed plants on Earth).
The legendary Carboniferous period ended when geological processes complicated the planet's topography, crushing its surface into folds and dismembering it with mountain ranges. Low-lying swamps were buried under a thick layer of sedimentary rocks washed away from the slopes. The continents changed their shape, displacing the sea and diverting ocean currents from their previous course, ice caps began to grow in places, and red sand covered vast expanses of land. Giant ferns, mosses and horsetails became extinct: their spores were not adapted to a harsher climate, and the attempt to reproduce by seeds turned out to be too weak and uncertain.
The first true seed plants.
The coal forests died and were covered with new layers of sand and clay, but some trees survived due to the fact that they formed winged seeds with a durable shell. Such seeds could spread faster, longer, and therefore over longer distances. All this increased their chances of finding conditions favorable for germination or waiting until they arrived.
The seeds were destined to revolutionize life on Earth at the beginning of the Mesozoic era. By this time, two types of trees - cycads and ginkgos - had escaped the sad fate of other Carboniferous vegetation. These groups began to co-populate the Mesozoic continents. Without encountering competition, they spread from Greenland to Antarctica, making the vegetation cover of our planet almost homogeneous. Their winged seeds traveled through mountain valleys, flew over lifeless rocks, and sprouted in sandy areas between stones and among alluvial gravel. Probably, small mosses and ferns that survived the climate change on the planet at the bottom of ravines, in the shadows of cliffs and along the shores of lakes helped them explore new places. They fertilized the soil with their organic remains, preparing its fertile layer for the settlement of larger species.
Mountain ranges and vast plains remained bare. Two types of “pioneer” trees with winged seeds, having spread across the planet, were tied to damp places, since their eggs were fertilized by flagellated, actively swimming sperm, like those of mosses and ferns.
Many spore-bearing plants produce spores different sizes– large megaspores, which give rise to female gametes, and small microspores, the division of which produces motile sperm. To fertilize an egg, they need to swim to it on water - a drop of rain and dew is enough.
In cycads and ginkgos, megaspores are not dispersed by the parent plant, but remain on it, turning into seeds, but the sperm are motile, so dampness is needed for fertilization. The external structure of these plants, especially their leaves, also brings them closer to their fern-like ancestors. Preservation ancient way fertilization by sperm floating in water led to the fact that, despite the relatively hardy seeds, prolonged drought remained an insurmountable problem for these plants, and the conquest of land was suspended.
The future of terrestrial vegetation was ensured by trees of a different type, growing among cycads and ginkgos, but having lost their flagellated spermatozoa. These were Araucarias (genus Araucaria), coniferous descendants of Carboniferous cordaites. During the era of cycads, Araucaria began to produce huge quantities of microscopic pollen grains, corresponding to microspores, but dry and dense. They were carried by the wind to the megaspores, or more precisely to the ovules with eggs formed from them, and germinate with pollen tubes that delivered immobile sperm to the female gametes.
Thus, pollen appeared in the world. The need for water for fertilization disappeared, and plants rose to a new evolutionary level. The production of pollen led to a colossal increase in the number of seeds developing on each individual tree, and consequently to the rapid spread of these plants. The ancient Araucarias also had a method of dispersal that has been preserved in modern conifers, with the help of hard winged seeds that are easily carried by the wind. So, the first conifers appeared, and over time, well-known species of the pine family.
Pine produces two types of cones. Men's length approx. 2.5 cm and 6 mm in diameter are grouped at the ends of the uppermost branches, often in bunches of a dozen or more, so that large tree there may be several thousand of them. They scatter pollen, covering everything around with yellow powder. Female cones are larger and grow lower on the tree than male ones. Each of their scales is shaped like a scoop - wide on the outside and tapering towards the base, with which it is attached to the woody axis of the cone. On the upper side of the scales, closer to this axis, two megaspores are openly located, awaiting pollination and fertilization. Pollen grains carried by the wind fly inside the female cones, roll down the scales to the ovules and come into contact with them, which is necessary for fertilization.
Cycads and ginkgos could not withstand competition with more advanced conifers, which, effectively dispersing pollen and winged seeds, not only pushed them aside, but also developed new, previously inaccessible corners of the land. The first dominant conifers were taxodiaceae (now they include, in particular, sequoias and swamp cypresses). Having spread throughout the world, these beautiful trees for the last time covered all parts of the world with uniform vegetation: their remains are found in Europe, North America, Siberia, China, Greenland, Alaska and Japan.
Flowering plants and their seeds.
Conifers, cycads and ginkgos belong to the so-called. gymnosperms. This means that their ovules are located openly on the seed scales. Flowering plants constitute the division of angiosperms: their ovules and the seeds developing from them are hidden from the external environment in the expanded base of the pistil, called the ovary.
As a result pollen grain cannot reach the ovule directly. For the fusion of gametes and the development of a seed, a completely new plant structure is required - a flower. Its male part is represented by stamens, the female part by pistils. They can be in the same flower or in different flowers, even on different plants, which in the latter case are called dioecious. Dioecious species include, for example, ash trees, hollies, poplars, willows, and date palms.
For fertilization to occur, the pollen grain must land on the top of the pistil—the sticky, sometimes feathery stigma—and stick to it. Stigma highlights chemical substances, under the influence of which the pollen grain germinates: living protoplasm, emerging from under its hard shell, forms a long pollen tube, penetrating the stigma, spreading further into the pistil along its elongated part (style) and ultimately reaching the ovary with ovules. Under the influence of chemical attractants, the nucleus of the male gamete moves along the pollen tube to the ovule, penetrates it through a tiny hole (micropyle) and merges with the nucleus of the egg. This is how fertilization occurs.
After this, the seed begins to develop - in a moist environment, abundantly supplied with nutrients, protected by the walls of the ovary from external influences. Parallel evolutionary transformations are also known in the animal world: external fertilization, typical of, say, fish, on land is replaced by internal, and the mammalian embryo is formed not in eggs laid in the external environment, as, for example, in typical reptiles, but inside the uterus. Isolation of the developing seed from extraneous influences allowed flowering plants to boldly “experiment” with its shape and structure, and this in turn led to an avalanche-like appearance of new forms of land plants, the diversity of which began to increase at a rate unprecedented in previous eras.
The contrast with gymnosperms is obvious. Their “naked” seeds lying on the surface of the scales, regardless of the type of plant, are approximately the same: drop-shaped, covered with a hard skin, to which a flat wing formed by the cells surrounding the seed is sometimes attached. It is not surprising that for many millions of years the form of gymnosperms remained very conservative: pines, spruces, firs, cedars, yews, and cypresses are very similar to each other. True, in junipers, yews and ginkgos the seeds can be confused with berries, but this does not change the overall picture - the extreme uniformity of the general structure of gymnosperms, the size, type and color of their seeds in comparison with the enormous wealth of flowering forms.
Despite the paucity of information about the first stages of the evolution of angiosperms, it is believed that they appeared towards the end of the Mesozoic era, which ended approximately 65 million years ago, and at the beginning of the Cenozoic era they had already conquered the world. The oldest flowering genus known to science is Claytonia. Its fossil remains were found in Greenland and Sardinia, i.e., it is likely that 155 million years ago it was as widespread as cycads. leaves Claytonia palmately complex, like those of modern horse chestnuts and lupins, and the fruits are berry-like with a diameter of 0.5 cm at the end of a thin stalk. Perhaps these plants were brown or green in color. The bright colors of angiosperm flowers and fruits appeared later, paralleling the evolution of insects and other animals that they were designed to attract. Berry Claytonia four-seeded; on it you can discern something resembling the remnant of a stigma.
In addition to extremely rare fossil remains, unusual modern plants, grouped under the order Gnetales, provide some insight into the first flowering plants. One of their representatives is the ephedra (genus Ephedra), found particularly in the deserts of the southwestern United States; outwardly it looks like several leafless rods extending from a thick stem. Another genus is Velvichia ( Welwitschia) grows in the desert off the southwestern coast of Africa, and the third is gnetum ( Gnetum) is a low shrub of the Indian and Malay tropics. These three genera can be considered "living fossils" demonstrating possible pathways for the transformation of gymnosperms into angiosperms. Conifer cones look like flowers: their scales are divided into two parts, reminiscent of petals. Velvichia has only two wide ribbon-like leaves up to 3 m long, completely different from conifer needles. Gnetum seeds are equipped with an additional shell, making them similar to angiosperm drupes. It is known that angiosperms differ from gymnosperms in the structure of their wood. Among the Gnetovs, it combines the characteristics of both groups.
Seed dispersal.
The vitality and diversity of the plant world depend on the ability of species to disperse. The parent plant is attached to one place by its roots all its life, therefore, its offspring must find another. This task of developing new space was entrusted to the seeds.
First, the pollen must land on the pistil of a flower of the same species, i.e. pollination must occur. Secondly, the pollen tube must reach the ovule, where the nuclei of the male and female gametes merge. Finally, the mature seed has to leave the parent plant. The probability that the seed will germinate and the seedling will successfully take root in a new place is an insignificant fraction of a percent, so plants are forced to rely on the law large numbers and disperse as many seeds as possible. The latter parameter is generally inversely proportional to their chances of survival. Let's compare, for example, the coconut tree and orchids. The coconut palm has the largest seeds in the plant world. They are able to swim indefinitely in the oceans until the waves throw them onto soft coastal sand, where the competition of seedlings with other plants will be much weaker than in the thicket of the forest. As a result, the chances of each of them taking root are quite high, and one mature palm tree, without risk to the species, usually produces only a few dozen seeds per year. Orchids, on the other hand, have the smallest seeds in the world; in tropical forests they are carried by weak air currents among high crowns and germinate in moist cracks in the bark on tree branches. The situation is complicated by the fact that on these branches they need to find a special type of fungus, without which germination is impossible: small orchid seeds do not contain nutrient reserves and in the first stages of seedling development they receive them from the fungus. It is not surprising that one fruit of a miniature orchid contains several thousand of these seeds.
Angiosperms are not limited to producing a variety of seeds through fertilization: the ovaries, and sometimes other parts of flowers, develop into unique seed-containing structures called fruits. The ovary can become a green bean, protecting the seeds until they ripen, turn into a durable coconut, capable of making long sea voyages, into a juicy apple, which an animal will eat in a secluded place, using the pulp, but not the seeds. Berries and drupes are a favorite delicacy for birds: the seeds of these fruits are not digested in their intestines and end up in the soil along with excrement, sometimes many kilometers from the parent plant. The fruits are winged and fluffy, and the shape of their volatile-increasing appendages is much more varied than that of pine seeds. The wing of the ash fruit resembles an oar, that of the elm it resembles the brim of a hat, that of the maple the paired fruits - biptera - resemble soaring birds, and that of the ailanthus fruit's wings are twisted at an angle to each other, forming, as it were, a propeller.
These devices allow flowering plants to use seeds very effectively for dispersal. external factors. However, some species do not count on outside help. Thus, the fruits of impatiens are a kind of catapult. Geraniums also use a similar mechanism. Inside their long fruit there is a rod, to which four, for the time being, straight and connected valves are attached - they are held firmly on top, weakly on bottom. When ripe, the lower ends of the valves break away from the base, curl sharply towards the top of the stem and scatter the seeds. In the ceanothus shrub, well known in America, the ovary turns into a berry, similar in structure to a time bomb. The pressure of the juice inside is so high that after ripening it is quite warm sunbeam so that its seeds scatter like living shrapnel in all directions. The boxes of ordinary violets, when dry, burst and scatter seeds around them. Witch hazel fruits operate on the principle of a howitzer: to make the seeds fall farther, they shoot them at a large angle to the horizon. In Virginia knotweed, in the place where the seeds are attached to the plant, a spring-like structure is formed that discards mature seeds. In oxalis, the fruit shells first swell, then crack and shrink so sharply that the seeds fly out through the cracks. Arceutobium is tiny, using hydraulic pressure inside the berries to push the seeds out of them like miniature torpedoes.
Seed viability.
The embryos of many seeds are provided with nutrients and do not suffer from drying out under an airtight shell, and therefore can wait for favorable conditions for many months and even years: for sweet clover and alfalfa - 20 years, for other legumes - more than 75, for wheat, barley and oats - to ten. Weed seeds have good viability: in curly sorrel, mullein, black mustard and peppermint, they germinate after lying in the ground for half a century. It is believed that 1 hectare of ordinary agricultural soil contains 1.5 tons of weed seeds, which are just waiting for the opportunity to get closer to the surface and sprout. Cassia and lotus seeds remain viable for centuries. The record for viability is still held by the seeds of the nut-bearing lotus, discovered several years ago in the bottom silt of one of the dry lakes in Manchuria. Radiocarbon dating has established that their age is 1040 ± 120 years.
