Leaf arrangement. The external structure of the leaf What is the leaf arrangement of maple lilac
Leaf classification
Distinguish between simple and compound leaves. Leaves that have one plate (solid or notched) are called simple. Simple leaves atl
Rice. 27. Compound Leaves: 1 - ternary; 2 - palmate; 3 - unpaired pinnate; 4 - paired pinnate.
compound leaves- - leaves, consisting of several clearly separated leaf blades (leaves), each of which is attached to a common petiole (rachis) with its petiole. Often a complex leaf falls off in parts: first the leaves, and then the petiole.
Depending on the location of the leaves, they distinguish (Fig. 27):
Pinnate leaves - leaves in which leaflets are located on the sides of the rachis. When the top of the rachis ends with one unpaired leaflet, such leaves are called pinnate(rosehip, white acacia). At parapinnate leaf, all the leaves have a pair (peas, yellow acacia).
Palmately complex leaves - leaves in which leaflets are not located along the length of the rachis, but only on its top in one plane (chestnut, lupine).
A special case of a complex leaf is trifoliate leaf - a leaf that has only three leaves (clover, sour).
The rachis of compound leaves can form lateral branches, then double-, thrice-four-pinnate leaves appear. For example, mimosa has a double-pinnate leaf.
Leaf venation
Venation- this is a system of conducting bundles in leaf blades.
Rice. 28. Leaf venation:
1 - parallel; 2 - arc; 3 - reticulate with a pinnate arrangement of the main veins; 4 - reticulate with a palmate arrangement of the main veins; 5 - dichotomous.
The nature of the arrangement of the veins and the shape of the leaf blades are closely related (Fig. 28). Distinguish:
simple venation- only one vein (mosses, club mosses) penetrates the leaf blade from the base to the top;
dichotomous venation- the leaf blade is pierced by forked branched veins (ginkgo);
arc venation- the leaf blade from the base to the top is pierced by several identical veins arranged in an arcuate manner (lily of the valley, hellebore);
parallel venation- the leaf blade from the base to the top is pierced by several identical veins, located strictly parallel (rye, sedge);
net venation- usually one vein enters the leaf blade from the petiole, which then gives branches - lateral veins, forming a dense network. Reticulate venation can be pinnate and palmate.
Linden (Tilia) is a deciduous tree with up to 45 species. It grows mainly in the temperate zone of the Northern Hemisphere. 7 common in Russia wild species and 10 hybrids. Small-leaved and heart-shaped linden is more common. In Ukraine and Moldova, mainly European, large-leaved, felt, Hungarian linden grows. In the Caucasus and Crimea - Crimean, Caucasian, pubescent columnar. On the Far East common Amur, Korean, Chinese, sprawling, Manchurian linden. In Tatarstan, Mordovia and Chuvashia, pure linden groves (linden forests) have been formed. The maximum age of linden forests is 400 years. AT single landings a tree can live up to 1200 years. On the streets of the city, the age of this plant is reduced to 100 years. Linden is a companion of oak, maple, ash, spruce and pine. The placement of the plant is uneven, depending on natural conditions and human activity. Under natural conditions, it reproduces by stump shoots.
The habitats of this plant can be forest lands and city streets. Artificially created linden plantations are found along roads, in parks, squares, gardens, around fields, apiaries, and reservoirs.
The most popular is the small-leaved linden, used in medicine and national economy. In Western Siberia, a species very close to it grows - the Siberian linden.
The linden tree is a source of pleasant, strong aroma, as well as effective tool in the fight against colds.
Trunk, bark and stalk of linden
In forest stands, trees have a straight, highly delimbed trunk and a highly raised, not dense crown. In free plantings, the crown is denser, located lower. The lower branches of the linden tree move away from the trunk and rise, the middle branches move horizontally from the trunk, the upper ones rise at an angle. The foliage of the tree is dark green, with hanging yellow-white flowers - half-umbels and yellow-green bracts. The shape of the crown is tent-shaped. The full formation of the crown ends at the age of 40 years.
The bark of a young linden is smooth, light gray, in adults it is thick, dark gray, covered with deep furrows and cracks.
The linden stem has a structure typical of all trees. In its center there are thin-walled cells of the core, where they accumulate nutrients. Surrounds the core thick layer wood, which makes up 90% of the total volume of the stem.
This plant is a scattered vascular spelowood non-core breed. It has a soft wood of white, pink, or reddish tint. It has a blurred, inexpressive texture, so the annual layers on the sections can be traced rather weakly. On the transverse section, narrow heart-shaped rays are visible in the form of thin lines, on radial cut you can see dim stripes and blurry dark spots. In terms of density, late wood does not differ from early wood. There are 4.5 annual layers per 1 cm cross section. The vessels are thin, inconspicuous. The structure of the wood is uniform. Moisture is evenly distributed over the trunk section.
Leaf arrangement and linden leaf
The linden leaf is simple, heart-shaped, pointed, the edges are finely serrated, with large veins, dark green above, light green below, with reddish hairs. It is held on a reddish petiole 1-3 cm long.
It contains calcium, therefore, when falling off, it quickly decomposes, thereby improving soil properties and increasing its fertility.
For 1 year, the mass of dry linden leaves during decomposition decreases by 70% of the initial mass.
Moreover, intensive decomposition occurs in the spring-summer period, the most favorable for the development of microorganisms in the soil. Freshly fallen leaves contain ash, potassium, calcium, nitrogen, sulfur.
Linden buds and root
Linden buds are reddish-brown, smooth, covered with scales, have an ovoid shape, arranged in two rows. Length 6-7 mm, width 3-5 mm. Each bud has 5 leaves with stipules and two rudimentary leaves. Shoots brown-brown, covered with lenticels.
The root system of the plant on fertile, fresh, loose soils is powerful, highly developed, has a tiered structure, uses nutrients from all soil layers. The linden root goes deep into the ground and gives well-developed lateral roots. Linden also has a superficial root system, formed by adventitious roots.
Flowers bisexual, small, correct form, collected in brushes (umbrellas), have 5 sepals, a corolla with 5 petals, a pistil and several stamens. Flowering begins in June, lasts until mid-July. Flowering time is up to 14 days. The tree begins to bloom from 20-25 years.
Flowering and nectar production depends on the habitat conditions of the plant, geographical, environmental and other factors. However, it has been observed that the linden begins to bloom when the bees have the maximum opportunity to use the nectar. Nectar in linden flowers is secreted by nectar-bearing tissue, held inside the sepals. The excreted nectar is not reabsorbed.
Linden branch and seeds
The period of maturation of the tree begins at the age of 20-30 years. The linden branch becomes strong enough to ensure flowering and seed maturation.
At this age appears a large number of inflorescences. Linden seeds ripen in autumn.
Spread by wind, animals and birds. They are especially noticeable on snowy crust. They are collected from October to March.
The fruit is a spherical, elongated nut containing 1, 2, rarely 3 seeds. The shell of the fruit is dense, waterproof.
Linden features
The plant is fairly shade tolerant. On this basis, it is second only to conifers, beech and oak. Shade-tolerant linden with a wide spreading crown often itself shades the soil to other plants. Frost-resistant. Among broad-leaved trees, it penetrates the farthest to the north, growing in harsh conditions with very low temperatures. It is not afraid of frost, as it blooms late. Frost resistance is due to the short growth period of the shoots, the high water retention capacity of the leaves, and the high oil content of the branches. Linden fats contain unsaturated linolenic acid, which quickly oxidizes and releases heat, so in winter, linden is able to withstand temperatures down to -50 ° C.
Sometimes on south side frost cracks form in the trunk and branches of the tree. This is due to a sharp temperature drop. In harsh winters with little snow, young shoots and roots can freeze. In some cases, the cause of death of young individuals may be the lack of insulation with a layer of snow. Strong winds also negatively affect the development of the plant. The tree is drought-resistant, but with excessive drought, growth is reduced. From the strong sun and dryness of the climate, the mosaic leaf arrangement of the linden saves, when the outer row forms a solid green ball, shading the area with the root system.
Linden does not like excessive soil moisture, waterlogging and flooding. Tolerates air pollution, smoke resistant. On the fertile soils its gas resistance increases. by the most unpretentious appearance This plant is considered small-leaved linden. It can grow on different soils, except for waterlogged, excessively salty and dry ones. Prefers loose, humus-rich areas.
The lindens growing in the zone of podzolic soils speak of the high fertility of the soil in this area. In the forest-steppe zone, the presence of linden indicates the leaching of the soil. The growth of the tree in the undergrowth of pine forests indicates highly productive conditions. This is due to the fact that the litter formed from leaves, needles, fallen branches and bark forms a neutral humus containing ash elements that reduce soil acidity and increase its degree of saturation.
After felling a tree, a stump is formed. It appears around the neck of the root and begins to sprout abundantly. The property of linden - to give dense shoots continues until old age. At the age of 100, this ability begins to decline. After clear-cutting, linden shoots begin to densely populate the cutting area, drowning out self-seeding and slowing down the growth of conifers.
Linden tolerates a haircut well, so its crown can be given any shape. This tree is often used to create parks, squares and alleys.
different. At the same time, they have a lot in common. Most plants have green leaves.
The leaves consist of a leaf blade and petiole (Fig. 123).
leaf blade
The leaf blade performs the main functions of the leaf.
Petiole
At the bottom, the leaf blade passes into the petiole - the narrowed stem-like part of the leaf. With the help of the petiole, the leaf is attached to the stem. Such leaves are called petiolate. Petiolate leaves have linden, birch, cherry, maple, apple tree.
In aloe, carnation, flax, tradescantia, lungwort, the leaves do not have petioles. Such leaves are called sessile (see Fig. 123). They are attached to the stem by the base of the leaf blade.
In some plants (rye, wheat, etc.), the base of the leaf grows and covers the stem (Fig. 125). Such an overgrown base gives the stem greater strength.
Stipules
In some plants, at the base of the petioles, there are stipules that look like films, scales, and small leaves-dots (Fig. 124). The main function of stipules is to protect young developing leaves. In peas, spring ranks and many other plants, stipules persist throughout the life of the leaf and perform the function of photosynthesis. In linden, birch, oak, membranous stipules fall in stages young leaf. In some plants, for example, in white acacia (locust locust), stipules are modified into spines and perform a protective function, protecting plants from damage by animals.
The leaves of most plants have sizes from 3 to 15 cm. The length of the leaves of some palms reaches 10 m or more. Floating, rounded with curved edges, leaf blades of victoria regia, which lives in the waters of the Amazon River, reach 2 m in diameter. Such a leaf easily holds a 3-year-old child on its surface. And in common heather, the length of the leaf is measured in just a few millimeters.
simple leaf
In linden, aspen, lilac, wheat, the leaves have only one leaf blade. Such leaves are called simple.
The shape of the leaf blades is varied: in aspen it is round, in lilac and linden it is heart-shaped, in wheat, barley it is linear, etc. (Fig. 126).
The leaf blades of oak and maple are divided by cutouts into lobes and are called lobed (Fig. 127). Dandelion leaves are separate, their cutouts are deeper. Cutouts of dissected leaves of yarrow and wormwood reach almost to the middle of the leaf.
complex sheet
Rowan, chestnut, acacia, strawberry, clover, lupine have complex leaves (Fig. 128). They have several leaf blades, which are attached to one main petiole with small petioles. During leaf fall, compound leaves do not fall entirely: first, the leaves fall off, then the petioles.
Veins are clearly visible on the underside of the leaf blades. These are conductive bundles of leaves (Fig. 129). They consist of conductive and mechanical tissues. The arrangement of vascular bundles in the leaves is called venation (Fig. 130).
Parallel venation
In iris, corn, wheat, the veins are parallel to one another. This is a parallel, or linear, venation.
Arc venation
Kupena, lily of the valley, plantain have arcuate venation - the veins go along the leaf in arcs.
Reticulate venation
In birch, oak, then the fields of veins on the leaves form a network. At the same time, lateral ones depart from the large central vein, which also branch. This venation is called reticulate. Reticulate veining can be palmate and pinnate.
Palmate venation
With palmate venation, several large veins extend radially from the base of the plate, like spread fingers (maple, etc.). material from the site
Pinnate venation
With pinnate venation, one main vein stands out, from which branching lateral ones (birch, bird cherry, oak, poplar, etc.) depart.
The leaves on the stem are arranged in such a way as to avoid shading one another.
Another leaf arrangement
Most often, the next leaf arrangement is observed - the leaves on the stem are placed one after the other (willow, oak, birch, cereals, blueberries, bell, apple, poplar).
Opposite leaf arrangement
With opposite leaf arrangement, the leaves are arranged in pairs, opposite each other (maple, lilac, spurge, honeysuckle, sage, mint).
Whorled leaf arrangement
If the leaves are arranged three or more in a node, this is a whorled leaf arrangement (common loosestrife, bedstraw, raven eye, oleander, elodea) (Fig. 131).
The shape of the leaves various plants are not similar to each other. But even the most diverse leaves can always be combined into two large groups. One group is formed by simple leaves, the other by compound leaves.
How to distinguish a simple sheet from a complex one? There is only one leaf blade on the petiole of each simple leaf. And compound leaves have several leaf blades located on the same petiole, which are called leaflets.
Among simple leaves Distinguish whole, lobed, separate and dissected.
Many trees have whole leaves: birch, linden, poplar, apple, pear, cherry, bird cherry, aspen and others. A leaf is considered whole if its blade is entire or has shallow grooves.
vaned a leaf is called, in which, like an oak, cut-blades along the edges of the plate reach one quarter of its width.
If the incisions of the leaf blade do not reach the midrib or base of the leaf a little, the leaves are called separate. If the leaf is cut to the midrib or to the base, it is called dissected.
lobed leaves- these are the leaves of maple, oak, hawthorn, currant, gooseberry and some other plants.
Take some leaves different plants, for example: raspberry, mountain ash, ash, poplar, maple, oak. Compare the leaves of rowan, raspberry, ash with the leaves of poplar, linden, maple and oak. How do they differ from each other? The leaves of ash, mountain ash and raspberry have several leaf blades - leaflets on one petiole. These are compound leaves. The leaves of poplar, maple and oak are simple. In simple leaves, the leaf blade falls off along with the petiole during leaf fall, while in complex leaves, the individual leaflets that make up the leaf may fall off earlier than the petiole.
A complex leaf consisting of three leaf blades, like a clover, is called ternary or tripartite.
If a leaf is formed by several leaf blades attached at one point, as, for example, in lupine, it is called palmately complex. If the leaves of a complex leaf are attached along the entire length of the petiole, then such a leaf is cirro-complex.
Among the pinnate leaves, there are unpaired and paired pinnate leaves.
Unpaired leaves are those that end leaf blade, which does not have its own pair. An example of pinnate leaves would be the leaves of rowan, ash, raspberry. Paired-pinnate leaves are less common, but you are still familiar with some plants with such leaves. These are, for example, sowing peas, mouse peas and sweet peas.
Both simple and compound leaves of dicotyledonous and monocotyledonous plants are arranged on stems in a certain order. The parts of the stem that bear the leaf are called stem nodes, and the sections of the stem between the nodes are internodes.
The arrangement of leaves on a stem is called leaf arrangement.
Most plants have an alternate leaf arrangement, for example: rye, wheat, birch, apple, sunflower, ficus, rose. Their leaves are arranged spirally around the stem one at a time, as if alternating with each other, which is why this arrangement is called alternate.
The leaves of lilac, jasmine, maple, fuchsia, deaf nettle are located on the stem not one at a time, but two at a time: one leaf against the other. Such a leaf arrangement is called opposite.
Sometimes there are plants with whorled leaf arrangement. Their leaves grow on the stem in bunches, whorls, arranged in three or more leaves per node, and form, as it were, a ring (whorl) around the stem. Among indoor plants whorled leaf arrangement has oleander, in the aquarium - elodea, among wild plants- northern bedstraw, lupine clover, four-leaf crow's eye and other herbaceous plants.