Flowers appear first... The moment of awakening: how the buds of different trees open When leaves appear on the trees in spring
When the days become shorter, and the sun no longer generously shares its warmth with the earth, one of the most beautiful times of the year begins - autumn. She, like a mysterious sorceress, changes the world around her and fills it with rich and unusual colors. These miracles occur most noticeably with plants and shrubs. They are one of the first to respond to weather changes and the onset of autumn. They have three whole months ahead to prepare for winter and part with their main decorations - leaves. However, first, the trees will certainly delight everyone around with the play of color and the madness of colors, and the fallen leaves will carefully cover the earth with their blanket and protect its smallest inhabitants from severe frosts.
Autumn changes in trees and shrubs, the reasons for these phenomena
In autumn, one of the most important changes in the life of trees and shrubs occurs: a change in the color of foliage and leaf fall. Each of these phenomena helps them prepare for winter and survive such a harsh time of year.
For deciduous trees and shrubs, one of the main problems in winter time year is a lack of moisture, so in the fall everything useful substances begin to accumulate in the roots and core, and the leaves fall off. Leaf fall helps not only to increase moisture reserves, but also to save them. The fact is that leaves evaporate liquid very strongly, which is very wasteful in winter. Coniferous trees, in turn, can afford to show off their needles even in the cold season, since the evaporation of liquid from them occurs very slowly.
Another reason for leaf fall is the high risk for branches to be broken under the pressure of a snow cap. If fluffy snow fell not only on the branches themselves, but also on their leaves, they would not be able to withstand such a heavy load.
In addition, over time, a lot of harmful substances, which can only be gotten rid of when leaves fall.
One of the recently uncovered mysteries is the fact that deciduous trees that are placed in a warm environment, and therefore do not need to prepare for cold weather, also shed their leaves. This suggests that leaf fall is associated not so much with the change seasons and preparation for winter, which is an important part of the life cycle of trees and shrubs.
Why do leaves change color in autumn?
With the onset of autumn, trees and shrubs decide to change the emerald color of their leaves to brighter and more unusual colors. At the same time, each tree has its own set of pigments - “paints”. These changes occur because the leaves contain a special substance, chlorophyll, which turns light into nutrients and gives the foliage green. When a tree or shrub begins to store moisture and it no longer reaches the emerald leaves, and the sunny day becomes much shorter, chlorophyll begins to break down into other pigments, which give the autumn world crimson and golden tones.
The brightness of autumn colors depends on weather conditions. If the weather outside is sunny and relatively warm, then autumn leaves will be bright and variegated, and if it rains often, then brown or dull yellow.
How the leaves of different trees and shrubs change color in autumn
Autumn owes its riot of colors and their unearthly beauty to the fact that the foliage of all trees has different combinations of colors and shades. The most common color of the leaves is purplish. Maple and aspen boast a crimson color. These trees are very beautiful in autumn.
The leaves of birch become light yellow, and those of oak, ash, linden, hornbeam and hazel become brownish-yellow.
Hazel (hazel)
The poplar quickly sheds its foliage; it just begins to turn yellow and has already fallen off.
Shrubs also delight with the variety and brightness of colors. Their foliage turns yellow, purple or red. Vine leaves (grapes are shrubs) acquire a unique dark purple color.
The leaves of barberry and cherry stand out against the general background with a crimson-red hue.
Barberry
Rowan leaves can be yellow to red in autumn.
The viburnum leaves turn red along with the berries.
Euonymus dresses in purple clothes.
The red and purple shades of foliage are determined by the pigment anthocyanin. An interesting fact is that it is completely absent from the leaves and can only be formed under the influence of cold. This means that the colder the days, the more crimson the surrounding leafy world will be.
However, there are plants that not only in autumn, but also in winter, retain their foliage and remain green. Thanks to such trees and shrubs, the winter landscape comes to life, and many animals and birds find their home in them. In the northern regions, such trees include: pine, spruce and cedar. To the south the number of such plants is even greater. Among them are trees and shrubs: juniper, myrtle, thuja, barberry, cypress, boxwood, mountain laurel, abelia.
Evergreen tree - spruce
Some deciduous shrubs also do not part with their emerald clothing. These include cranberries and lingonberries. On Far East There is an interesting wild rosemary plant, the leaves of which do not change color in the fall, but curl up into a tube in the fall and fall off.
Why do the leaves fall but there are no needles?
Leaves play an important role in the life of trees and shrubs. They help create and store nutrients and also accumulate mineral components. However, in winter, when there is an acute lack of light, and, therefore, nutrition, the leaves only increase the consumption of useful components and cause excessive evaporation of moisture.
Coniferous plants, which most often grow in areas with a rather harsh climate, are in great need of nutrition, so they do not shed their needles, which act as leaves. The needles are perfectly adapted to cold weather. The needles contain a lot of chlorophyll pigment, which converts nutrients from light. In addition, they have a small area, which significantly reduces the evaporation of much-needed moisture from their surface in winter. The needles are protected from the cold by a special wax coating, and thanks to the substance they contain, they do not freeze even in severe frosts. The air that the needles capture creates a kind of insulating layer around the tree.
The only coniferous plant that leaves its needles for the winter is larch. It appeared in ancient times, when summers were very hot and winters incredibly frosty. This climate feature led to the fact that the larch began to shed its needles and there was no need to protect them from the cold.
Leaf fall, as a seasonal phenomenon, occurs in each plant at its own specific time. It depends on the type of tree, its age and climate conditions.
Poplar and oak are the first to part with their leaves, then the time comes for rowan. The apple tree is one of the last to shed its leaves, and even in winter, there may still be a few leaves left on it.
Poplar leaf fall begins at the end of September, and by mid-October it completely ends. Young trees retain their foliage longer and turn yellow later.
The oak begins to lose its leaves at the beginning of September and after a month it completely loses its crown. If frosts start earlier, leaf fall occurs much faster. Along with the oak leaves, acorns also begin to fall off.
Rowan begins its leaf fall in early October and continues to delight with its pink leaves until November 1st. It is believed that after the rowan leaves its last leaves, dank, chilly days begin.
The leaves on the apple tree begin to turn golden by September 20th. By the end of this month, leaf fall begins. The last leaves fall from the apple tree in the second half of October.
Evergreen plants and shrubs do not lose their foliage even with the onset of cold weather, as ordinary ones do hardwoods. Constant foliage cover allows them to survive any weather conditions and retain the maximum supply of nutrients. Of course, such trees and shrubs renew their leaves, but this process occurs gradually and almost imperceptibly.
Evergreens do not shed all their leaves at once for several reasons. Firstly, then they do not have to spend large reserves of nutrients and energy to grow young leaves in the spring, and secondly, their constant presence ensures continuous nutrition of the trunk and roots. Most often, evergreen trees and shrubs grow in areas with mild and warm climates, where the weather is warm even in winter, however, they are also found in harsh climates. climatic conditions. These plants are most common in tropical rainforests.
Evergreen plants such as cypresses, spruces, eucalyptus trees, some types of evergreen oaks, and rhodendron can be found over a wide area from harsh Siberia to the forests of South America.
One of the most beautiful evergreens is the blue fan palm, which grows in California.
The Mediterranean oleander shrub is distinguished by its unusual appearance and height of more than 3 meters.
Another evergreen shrub is gardenia jasmine. Its homeland is China.
Autumn is one of the most beautiful and vibrant times of the year. Flashes of purple and golden leaves preparing to cover the ground with a multi-colored carpet, coniferous trees piercing the first snow with their thin needles and evergreens, always pleasing to the eye, make the autumn world even more delightful and unforgettable. Nature is gradually preparing for winter and does not even suspect how fascinating these preparations are to the eye.
In this article we have collected material on the topic “tree leaves” and “tree structure”. Acquaintance with a tree begins for a child in his earliest childhood.
Each yard has its own good-natured giant, who will happily provide shelter from the scorching sun, rain, and share fallen leaves and dry twigs for everyone. However, many children perceive trees as nameless companions, without thinking that each of them has its own name, has a complex structure and performs important tasks. Therefore, with a deeper study of trees, kids make many discoveries for themselves.
For example, children will be interested in learning what parts a tree consists of. To do this, we use a schematic image of a tree and talk about each part of it:
- The roots of a tree are its foundation. They feed the tree by absorbing nutrients dissolved in the water and also keep it upright. The larger the tree, the richer its root system.
- The trunk of a tree is like its body. All substances extracted by the roots pass upward along the trunk, and branches begin to extend from the trunk. It is important to note that a real tree has one trunk, but shrubs have several, even large, trunks.
- Tree branches - support for leaves; It is on the branches that buds are formed, from which leaves and flowers then appear. Nutrients also pass through them. Over time, the branches become wider and harder (woody), and new branches appear from them.
- The foliage of a tree is an organ that allows the tree to exchange substances with the environment. Thanks to the leaves, the tree absorbs carbon dioxide, which is harmful to humans, from the air, and here from it under the influence sun rays Organic substances are formed, and through the leaves the tree releases oxygen that we breathe.
- All the leaves and branches of the tree form its crown - a lush cap that provides shade and shelters us from the rain.
Having studied the structure of a tree, you can move on to the next stage - find out how it comes into being. Where and how do trees grow? The answer to this question can be depicted in the form of a circular diagram.
So, let’s look at the entire life cycle of a fruit tree:
The seed is the source of life for every plant, including trees. It contains a small embryo and the initial supply of nutrients that the embryo needs in order to germinate through the seed coat. Once in the soil, the embryo begins to actively develop, hatches through the shell, grows and sends out roots, with which it absorbs from the ground the substances necessary for its growth.
After many years, the embryo turns into a tree, which, having reached a certain age, acquires the ability to reproduce its own kind.
In the spring, buds form on the branches of the tree, in which an organ of amazing beauty and smell develops - a flower.
The flower of a fruit tree is designed in such a way that when pollinated (by wind or insects), a small rudiment of the fruit is formed in it.
The beginning of its development and rapid growth occurs in the spring, when buds are actively formed on the branches, from which leaves and flowers subsequently appear. It is not without reason that they say that in spring trees come to life after winter sleep.
In summer, trees appear before us in all their glory. They constantly interact with the outside world, feed, and replenish supplies of substances necessary for their life. Tree leaves work continuously in the summer, turning into a real factory for processing carbon dioxide and producing oxygen and nutrients from it.
All vital processes in the tree decline: daylight hours become shorter, and the amount of sunlight is not enough for the formation of new chlorophyll molecules in the leaves, so the foliage gradually changes its color and falls off. Falling leaves not only saves the tree's strength, which it will need to survive the harsh winter, but also saves tree branches from breaking off, which can occur under the weight of fallen snow.
The tree seems to freeze. It economically uses the reserves accumulated over the summer and looks forward to the arrival of the first spring warmth.
But not all trees go through such a cycle of transformations, but only those that have leaves, that is, deciduous. But trees whose branches are covered with needles (conifers) look the same all winter as they do in summer.
Most famous conifer- This . Of course, it became famous thanks to the Russian tradition of decorating spruce branches on New Year's Eve. Spruce reproduces with the help of cones that form during the summer.
But the most common deciduous trees are:
- - a tree with bright berries and beautiful jagged foliage that looks especially impressive in the fall. There is a version that it was called rowan because its leaves are quite small and, when the wind blows, they tremble, causing ripples in the eyes of those who look at it.
- Birch is a symbol of Russia, a unique tree with white bark. Its very name comes from a Slavic word meaning “to glow, to turn white.” Birch is also interesting for its flowers, which look like earrings, and the fact that its branches are very long and thin, they seem to hang down.
- Poplar is a frequent companion of human habitation. Poplars are planted near houses because they grow quickly, which means they begin to purify the air early and absorb excess moisture well. In the wild, poplar is often found in wetlands, which is why it got its name, which translated from Slavic means “swampy place, swamp.” Poplar fruits are capsules from which seeds fall out, covered with many silky hairs - poplar fluff. This fluff causes a lot of inconvenience to people, so poplars are often pruned, leaving only non-fruit-bearing branches at the top.
- Oak is a giant tree, especially revered by our ancestors. Its fruits - acorns - were used to prepare a drink that replaced coffee, but people found even greater use of oak bark and wood, which is distinguished by its strength and beautiful color.
- Maple - owner beautiful leaves with sharp edges. Sweet, aromatic maple syrup is obtained from its sap.
- Elm is a tree whose wood, branches and bark have been used by people since ancient times to make furniture, tools and even weapons. Elm bark (bast) is strong and flexible, it was tied various items, for which the tree got its name. Shoes were woven from bast.
- Chestnut is a tree with unusual fruits, the core of which resembles a nut. It is believed that the word “chestnut” has the same root as the word “porridge”, since the fruits of the chestnut were often eaten.
- Willow is a tree with unusual long branches and narrow leaves. Its name comes from the word “twist”, which is explained by the main use of willow branches - they were used to twist baskets and weave furniture.
In order to better remember the names of trees, you can play simple game: mix cards with pictures of leaves and trees themselves, and then match them and name them.
The leaves can be used to make a very interesting visual aid for children. To do this, you will need to collect leaves of different types and laminate them.
We cut out the leaves slightly away from the edge.
We have a live guide to learning the types of leaves.
Print out the names of the trees where you collected the leaves from on a separate piece of paper. We compare the name of the tree with the leaf itself, studying and remembering its shape and structural features.
Images of leaves are more clear on coloring pages, where you can examine their outline and color them depending on the expected time of year and the shades characteristic of a particular tree.
Birch coloring page Alder opens the flowering season for trees. Its inflorescences are inconspicuous, but still, during the period of mass flowering, they will certainly attract attention if at this time we pass somewhere along the bank of a stream or near a ravine, where alders are usually found. Even from a distance you can see the reddish tint of the tree crown. As we get closer, we will see a large number of drooping catkins, which, at the slightest tap on the trunk or a blow of wind, will throw out whole clouds of yellow dust. In addition to these earrings, we will also find numerous black cones on the alder. While the catkins represent the male inflorescences of the alder, these cones are last year's female inflorescences, which still continue to hang on the tree and fall off only at the beginning of summer.
Almost simultaneously with the alder in early spring, when there are still snowdrifts in the depths of the forest, hazel or hazel, a common and well-known shrub in our forests, blooms at the edge, on the sun-baked slopes. However, hazel is popular only in the fall, when its fruits ripen; in the spring no one pays attention to it, especially when it stands in a leafless state. Meanwhile, it was precisely at this time that he was perhaps most interesting from a biological point of view. The flowering of the hazel tree is taken by some phenologists to mark the beginning of the third period of spring, which at this time finally comes into its own.
First flowering shrub 
Almost simultaneously with the alder in early spring, when there are still snowdrifts in the depths of the forest, hazel or hazel, a common shrub known to everyone in our forests, blooms at the edge of the forest, on the sun-baked slopes. However, hazel is popular only in the fall, when its fruits ripen; in the spring no one pays attention to it, especially when it stands in a leafless state. Meanwhile, it was precisely at this time that he was perhaps most interesting from a biological point of view. The flowering of the hazel tree is taken by some phenologists to mark the beginning of the third period of spring, which at this time finally comes into its own. At this time, warm sunny days are usually already established, the snow is quickly melting and the awakening of the plant world is becoming more noticeable every day. If the birch and maple, with the beginning of their sap flow, seemed to catch the first glimpses of the coming spring, then the modest flowers of the hazel mark its complete turnaround, the final victory over winter.
Early flowering of hazel, as well as alder, is possible only thanks to the advance preparation of its inflorescences. Throughout the winter, on its branches we observe male earrings, in which there are fully formed flowers. They can withstand frosts of thirty degrees, but as soon as they begin to develop, they become much more sensitive to low temperatures and during the flowering period they often suffer from frosts. At first glance, the structure of men's hazel earrings resembles the already familiar alder earrings.
The development of flower catkins in spring occurs with exceptional speed. As soon as the sun warms up and the temperature rises, the earrings begin to crack, and the stem on which the flowers sit stretches and grows almost before our eyes. For example, on a cut hazel branch in a humid chamber, the stem of a male catkin lengthened by as much as 3 cm in one day. The rate of cracking of anthers is closely dependent on the degree of air humidity. In a humid atmosphere, the opening of the anthers is delayed for several days, but if you move the earring to a dry place, it occurs within half an hour. This circumstance is of great importance in the life of the plant. It allows him to wait out rainy weather and postpone flowering until a more favorable time. However, in rainy weather, the already opened anther cracks have the ability to close again. This also significantly reduces pollen waste. The amount of pollen released by hazel trees during the flowering period is enormous. One earring produces about 4 million pollen grains, and if we accept that there will be at least a hundred such earrings on an average bush, and in fact much more, then you can imagine what a colossal number of tiny dust particles float in the air in our forests in the spring. Let us now turn to the female hazel flowers. Unlike males, they are hidden in the bud in winter and become noticeable only in spring, when purple tassels of stigmas appear from the scales.
Does the intense red color of the stigmas have any biological significance? Many people have probably noticed that young leaves developing from buds in the spring or sprouts of herbaceous perennial plants are bright red in color. It is clearly visible on large sprouts of horse sorrel or on young leaves of maple, cherry or oak. This red color is explained by the presence in plant tissues of a special pigment - anthocyanin, dissolved in cell sap. We will dwell on it in more detail in the chapter on leaf fall, but now we will point out that anthocyanin is currently attributed to the role of an additional catcher from weta. By absorbing green and blue rays of the spectrum, it helps to increase the temperature in cells, which in cool spring time is of great importance. It is believed that the intense pink color of the hazel stigmas, as well as the purple color of the female alder inflorescences, thus accelerates the germination of pollen on the stigmas, which occurs more vigorously in conditions of elevated temperature.
When do hazel buds form?
The unfolding of hazel leaves occurs much later than its flowering. Only after the male catkins lose dust, darken, dry out and begin to fall from the branches, do the buds begin to bloom, covering the bush with a delicate green haze. Why do leaf buds bloom much later than female flower buds or male catkins? Why does our shrub develop with such a natural sequence, first opening its huge flowers and then dressing in its green outfit? It can be assumed that in the hazel, as well as in most of our other trees and shrubs that bloom before the leaves bloom, the development of floral buds and the development of vegetative buds are different stages, the onset of which requires different temperature conditions. The development of vegetative buds requires significantly more heat than the development of floral buds. Hazel buds, having begun their development, subsequently bloom extremely quickly, since they contain all the necessary parts already from the previous year. This formation of buds occurs much earlier than is usually imagined, and already in the middle of summer, fully formed buds can always be found on young shoots of most of our trees and shrubs. For example, on May 25, buds consisting of 6-10 scales were observed on young growing hazel shoots. On June 10, these buds already had 12-14 scales, but leaf primordia were not yet noticeable among them. They appeared in the buds at the beginning of July, first in the amount of one or two, and by August 11 the next 2 - 3 leaves had developed.
It is remarkable that even at this time in the axils of these tiny leaves, under strong magnification, small buds of two to four scales could be detected. These bud rudiments must therefore overwinter twice before they begin to develop. This is how long the development path of hazel buds goes before they become noticeable or we pay attention to them!
What are kidney scales? 
In most plants, for example, willow, hawthorn, rose hip, etc., in adult leaves we can distinguish three main parts - the leaf blade, which serves to supply light to the plants, the petiole, which supports the leaf blade and attaches it to the stem, and, finally, stipules. Stipules usually look like two small leaves located at the base of the leaf petiole, and their purpose is not always clear at first glance. However, the significant role they play in plant life becomes clear in the spring, when the buds on the trees begin to develop. It turns out that in the hazel, as in most of our trees and shrubs, the bud scales, which play such a significant role in the life of plants in winter, are nothing more than stipules, which in the bud are significantly ahead of their development in the corresponding leaves. In hazel, the stipules fall off, having fulfilled their purpose, immediately after the shoot develops, and in the summer it is no longer possible to find them on the shoots. In linden, this shedding of stipules at the moment the leaves bloom is so noticeable that in linden forests in the spring the entire soil under the trees is strewn with pinkish or slightly green bud scales. In other trees, stipules remain throughout the life of the plant. They turn green and take part in assimilation. However, one should not think that in all our trees and shrubs the bud scales are formed by stipules. Currants are completely devoid of stipules, and in its buds the scales represent expanded leaf petioles. In horse chestnut, the bud scales are modified leaf blades. It is not difficult to be convinced of this at the moment of the blossoming of its large buds, where all the transitions between the bud scales and real leaves can be easily observed. We now know what the bud scales of the hazel tree are. Let's see how they work. There is one interesting detail here. If we make a cross section through the kidney scale and look at it under a microscope, we will find a special cavity inside. This cavity is filled with air, which is known to be a very poor conductor of heat. As a result of this, the protective role of scales increases, which protect delicate leaf primordia from sudden temperature fluctuations.
After the hazel shoot has completed its development - flowering, the deployment of growth buds, the growth of shoots and the formation of new buds, we will not notice any further significant changes. However, in the summer, important processes of seed ripening in fertilized ovaries and the deposition of reserve substances in leaf buds and flower male catkins occur, which ensures their development next spring.
Hazel seeds ripen extremely slowly. Despite the fact that this shrub blooms extremely early, its fruits only fully ripen by September. This makes it sharply different from our other trees and shrubs, the fruiting period of which is much shorter. It is especially curious that the period of fruit ripening for willow and aspen usually does not exceed a month, while for hazel it is on average four months. What are these characteristics of fruiting associated with? various plants It’s hard to say, however, in the future we will partially return to this issue.
Our willows in early spring
In early spring among our wind-pollinated trees and bushes hung with modest, inconspicuous earrings, flowering bushes and even from afar they attract attention. At this time, bright yellow willow inflorescences, thickly covered with sticky pollen and emitting a subtle and pleasant aroma, stand out sharply against the gray, still transparent background of the forest. However, long before flowering, many willows, especially the red willow, become quite noticeable thanks to their graceful fluffy inflorescences, known as “lamblets”. The sudden appearance of these “lambs” in the middle of winter, in January or February, is one of the most curious phenomena in the life of our spring nature. However, before getting acquainted with the life characteristics of willows, it is necessary to note that we have a large number of species. In total, in the flora of the USSR there are currently about 170 species of willows, and in the Moscow region alone their number reaches 40. With such species diversity, willows have the ability to produce crosses with each other, often double and triple. Currently, even quintuple and quintuple crosses are known, which are extremely difficult to understand. We will refer only to some of the most famous and common willows among those that bloom in early spring before the leaves bloom. This includes the well-known red willow, or red willow (Salix purpurea), widespread in the south of the European part of the USSR, reaching in the north to the southern border of the Moscow region and introduced into culture; goat willow, or willow-bredina (Salix caprea), ubiquitous in forests, and ash willow (S. cinerea), growing in damp places in most of the USSR. Other willows that are widespread in our country, such as white willow (Salix alba) or Brittle willow (Salix fragilis), growing along the banks of ponds and near houses in the form of large weeping trees, bloom much later, simultaneously with the development of young leaves.
When willow flower buds awaken from winter sleep 
The dormant period for our early willows lasts until mid-January. Until this time, their buds are tightly covered with scales and do not show any noticeable changes. However, starting from the end of January, flower buds begin to show unmistakable signs of incipient development. The caps crack at the very base and, not being able to cover the swelling flower earring, gradually move towards its top or to the side, and then completely fall off. However, this process proceeds at an extremely slow pace and usually ends completely only by the second half of March.
The shedding of caps in our early willows is an extremely interesting phenomenon. In February there are the most low temperatures, there are often twenty-degree frosts and the soil freezes to its maximum depth. However, the swelling of flower catkins undoubtedly indicates the beginning of plant development and their emergence from winter torpor. The life of our trees in winter has not yet been sufficiently studied, however, there is reason to believe that during periods of thaw and on warm sunny days, sap flow begins in individual branches of willows. In them, the transformation of reserve substances occurs and their movement to the buds from various parts of the crown and trunk.
Let us now follow further the development of flower earrings in willow. Having shed their caps, they look like graceful, fluffy white balls, looking from a distance like small tufts of cotton wool. What do their numerous hairs represent? The best time to answer this question is when the willow tree is in bloom. At this time, it is not difficult to notice that willow inflorescences come in two varieties: both male and female, and they are located on different bushes in such a way that one bush has only male catkins, and the other has female ones.
The male flowers of willows are constructed very simply. They are devoid of perianth and are covered with only one scale in the axil, in which there are usually two (some willows have more) stamens. The scales are usually two-colored: yellowish-green below, blackish above. Upper part The scales are covered with long, numerous hairs, which give the still unbloomed earring a characteristic fluffy appearance. The significance of these hairs in the life of the plant is quite clear. By dressing the buds like a fur coat, they give them the opportunity to withstand low temperatures and its sharp fluctuations without any harm at a time when the caps covering them fall off. Female flowers of willows have a similar structure, except that instead of stamens there is an oblong ovary, thickened downward, resembling a bottle in shape. This ovary at the top turns into a style with a bipartite stigma, the sticky surface of which catches pollen falling on it. In addition to scales, stamens and pistils, male and female willow flowers have special nectaries at the base of the covering scales that secrete sweet nectar juice. Willows, unlike most of our other early flowering trees and shrubs are pollinated with the help of insects, which are attracted, on the one hand, by fragrant nectar, and on the other, by a large amount of pollen, which densely clings to flower catkins during the flowering period.
Such a simple structure of flowers in our willows, devoid of any traces of perianth, somehow does not fit with their method of pollination; in addition, all the other, by the way, more ancient representatives of the willow family - various poplars and aspen - are typical wind-pollinated plants. Therefore, it is currently believed that willows are secondarily adapted to pollination with the help of insects, and this adaptation could have arisen in relatively recent times. This is indicated, by the way, large number There are up to eighty species of insects visiting willow flowers. Among them we will meet bumblebees, common and ground bees, butterflies and some flies. This diverse assortment of pollinators indicates that willows have no particular specialization in this direction, whereas the flowers of most other entomophilous plants are strictly adapted to a particular species or group of insects. We will look at some of these devices in the next chapter.
It is also interesting to note that at present there is reason to believe that the ancestors of our willows had bisexual flowers, as indicated by the not so rare appearance of special freaks in the goat willow in the form of flowers that have both a pistil and stamens. It is possible that the transition to dioecy gave willows a number of advantages in terms of protection against self-pollination. However, all this still remains in the realm of the most distant assumptions.
Despite the apparent chaos and disorder, in most plants the leaves are located on the stems and branches so correctly that it is possible to determine their location general rules.
Upon superficial observation, it seems as if most often the leaves are arranged without any order, that they are scattered, as they still say in most descriptive writings (folia sparsa). Only in those plants in which each stem node bears more than one leaf, the correctness of leaf arrangement is striking and has long been noticed. If the leaves sit in pairs and one against the other, then it is rightly expressed about them that they are opposite, or opposite (folia opposita).
In this case, it almost always happens that leaf pairs alternate with each other - then the leaves of the nearest pairs are crosswise to each other, the leaves of the third pair, counting from the bottom, are directly above the leaves of the first pair, the leaves of the 4th are above the leaves of the 2nd, etc. To denote this circumstance, the expression sitting crosswise (f. f. decussata) is used. This happens, for example, in our maples, in lilacs, in all Lamiaceae (mint, sage, etc.). Instead of two leaves on one node there are 3 leaves, for example. in oleander, and then the nearest leaves of such triple rings or circles also alternate with each other; There are also known plants that have 4, 6, 10 or even more leaves on each node (many madder, Hippuris, etc.).
But even in these cases, the leaves of the nearest circles alternate. Such leaves can be called annulate, or ringed (f. f. verticillata). Paired and opposite, obviously, belong here, only the number of leaves in their circles is reduced to the smallest. If on stems with ring-shaped leaves you mentally connect all the leaves sitting on top of each other, you will get several vertical and parallel lines, which are called orthostic. The number of such orthostic poems will obviously be doubled more number leaves in this circle. The regularity that comes from here is so clear that, for example, in plants with opposite leaves, especially if there are many leaves, their four orthostics are visible at first glance. The scattered leaves represent a different kind of rightness. Stems and branches with such leaves produce one leaf at each node.
If we start from any sheet, for example. from the bottom one, we mentally draw a line to the nearest sheet, and from the second again to the nearest one, etc. until the end, then this line will turn out to be a helical one, and on a horizontal projection it will be a spiral one. Therefore, the leaf itself is called spiral, the leaves are spirally arranged (f. f. spiraliter posita).
This turns out to be the following. Going in a spiral, for example. upward from this sheet, we reach the one that falls above the first one (from which we started). In some plants, like linden, this leaf is always the 3rd, above the 2nd there is a 4th, above the 3rd there is a 5th, etc.; in others, like alder, the 4th is above the 1st, the 5th is above the 2nd, etc.; in others, for example. in aspen, above the 1st there is a 6th, above the 2nd - a 7th, etc. If you draw vertical lines through all mutually covering leaves, then their number will be equal to the number of leaves located between two mutually covering leaves: for linden - 2nd, for alder - 3rd, for aspen - 5.
If you measure the horizontal distance between the ortostichs, it will turn out to be constant for each plant and will be equal to the segment of the spiral connecting 2 mutually covering leaves. This segment is called a complete cycle of leaf arrangement. In some plants (linden, alder) it makes one revolution around the stem, in others (aspen, poplar, apple tree) it makes 2 revolutions, in others (Carduus) - 3 revolutions, etc. This distance is measured by the arc and the corresponding angle , between two nearest leaves is called the divergence (divergentia) of the leaves, and the angle measuring the amount of divergence is the angle of divergence (angulus divergentiae).
It is clear that this angle depends on the number of revolutions in a full cycle and on the number of leaves located along the line full cycle. If there is one revolution, i.e. one circle, and there are 2 leaves in the cycle, then to find the divergence angle you need to divide the circle in two, you get a divergence angle of 1/2, where 1 means the number of revolutions in the cycle, and 2 is the number of those located on it leaves; if the number of leaves is 3, then the circle is divided by 3, you get a discrepancy of 1/3, if the number of revolutions is 2 (i.e., 2 circles), and there are 5 leaves, then these 2 circles should obviously be divided by 5, you get a discrepancy of 2/5, where 2 again means the number of revolutions, and 5 is the number of leaves of the cycle.
Studying many plants, it was found that in nature there are very different discrepancies, but most often in nature the following are found: 1/2, 1/3, 2/5, 3/8, 5/13, 8/21, etc. , but of these, the first three are the most common. Each of these fractions, meaning a divergence, at the same time, obviously, means the leaf itself, indicating in the denominator the number of leaves in the cycle and the number of vertical rows (orthos) formed by them, and in the numerator - the number of revolutions of the spiral in a full cycle .
Therefore, each leaf arrangement can be indicated by the number of leaf rows, or orthostic: they are called two-row (1/2), three-row (1/3), etc. In nature, however, in addition to those divergences that are indicated in the above series of fractions, called the main thing, since it comes across much more often than others, there are other rows, for example. 1/3, 1/4, 2/7, etc. or 1/4, 1/5, 2/9, etc. In all these series of discrepancies it is noticed that each subsequent fraction is obtained by adding the numerators and denominators of the previous two, which, however, does not indicate any legality in the very nature of plants.
For a visual representation of leaves, it is convenient to represent them on a horizontal projection, obtained by mentally drawing verticals from the points of attachment of leaves with the vertical position of the leafy stem itself. Points of intersection of verticals (perpendiculars) with horizontal plane, obviously, will be arranged in the same way as the leaves are located on the stem. Instead of dots, arcs are usually drawn, meaning leaves (their cross-section), thickening the arcs in those places where dots appear on the projection, i.e., in the middle of each arc. Such a drawing represents a plan of a leafy shoot, since a circle is drawn in the middle of it, indicating a cross section of the stem itself. This plan is a diagram of a leaf-bearing shoot. The diagrams clearly show the number of leaves of the cycle, their relative position and the angle of divergence.
They are used most of all in the study of inflorescences and flowers. The correct arrangement of leaves, although observed in most plants, is known to have exceptions, that is, plants in which the divergence is not constant. In addition, the divergence often changes when moving from the main stem to the branches, which, however, always occurs in the same way. It should also be noted that in many plants the rows of mutually covering leaves, although they remain parallel, do not appear vertical, but curved. In each polynomial L. it is always possible to open, in addition to the main helical line, or spiral, which passes through all the leaves of the shoot, also secondary, steeper spirals, directed in 2 opposite sides.
These minor spirals are called parastichy. Parastichs of one direction, taken together, obviously also capture all the leaves of the shoot, but each of them only a certain part of them, namely 1/2 of all leaves, if there are 2 parastichs of the same name, one third - if there are three of them, etc., which already follows from the fact that they are parallel and cover all the leaves of the shoot. If the main spiral is very gentle and is not noticeable, as happens on shoots with very numerous flowers, then parastichy are used to open the main spiral. To do this, you need to renumber all the leaves on the parastiches of one and the other direction, starting from any one, making sure that there is a difference between the numbers, equal to the number parastich.
After renumbering all the parastichy, the main spiral appears by itself. The correctness in the arrangement of leaves, revealed and depicted using the method presented above, is in close connection with the development and internal structure plants, it also corresponds to the need for plants to adapt to environmental conditions, but a physiological explanation has not yet been found.
Research by Nägeli, Hoffmeister, and Schwendener showed that in many cases, leaf growth at the beginning of shoot development, when the leaves look like small tubercles, is different than at the end of development. The last of the named scientists also showed that due to the slower growth of the leaf-bearing shoot compared to the growth of the leaves themselves, the leaves undergo mutual pressure, shift in certain directions and change their position, finally settling according to a well-known formula only at the completion of their development.
These studies, while explaining the previously noted difference between the arrangement of leaves at the beginning and at the end, do not, however, provide a complete mechanical explanation, since in many cases, for example. on shoots with opposite leaves, these leaves are located from the very beginning in the same way as they are located at the end. Science owes the thorough study and formulation of L. most of all to Alexander Brown, Schimper and the Bravais brothers.
Literature. A. Braun, "Vergleichende Untersuchung ueber die Ordnung der Schuppen an der Tannenzapfen" ("Abhandlungen der Leopoldinisch-K arolinischen Akademie", vol. 14); L. F. et A. Bravais, “Essai sur la disposition des feuilles curvis érié es” (“An. d. sc. nat.”, 1837, vol. 7); they also, “Essai sur la disposition des feuilles rectis érié es” (“An. des sc. nat.”, 1838); S. Schimper, "Ueber die M öeglichkeit eines Wissenschaftlichen Verstä ndnisses der Blatt-Stellung, mitgetheilt von A. Braun" ("Flora", 1835, Nos. 10, 11 and 12); Simon Schwendener, "Mechanische Theorie der Blattstellungen" (Lpc., 1878).
