The shape of the leaves of different plants is not similar to each other. But even the most diverse leaves can always be combined into two large groups. One group consists of simple leaves, the other - complex 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 one petiole, which are called leaflets.
Among simple leaves, there are whole, lobed, divided and dissected leaves.
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 notches.
Bladed they call a leaf in which, like an oak, the cut-out blades along the edges of the blade reach one quarter of its width.
If the cuts in the leaf blade do not reach the midrib or base of the leaf slightly, the leaves are called divided. 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 several leaves of different plants, for example: raspberry, rowan, ash, poplar, maple, oak. Compare the leaves of rowan, raspberry, and ash with the leaves of poplar, linden, maple and oak. How are they different from each other? The leaves of ash, rowan 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 leaves that make up the leaf may fall off earlier than the petiole.
A compound leaf consisting of three leaf blades, like a clover, is called trisyllabic or trifoliate.
If a leaf is formed by several leaf blades attached at one point, as, for example, in lupine, it is called palmate compound. If the leaves of a compound leaf are attached along the entire length of the petiole, then such a leaf is pinnately complex.
Among pinnately compound leaves, a distinction is made between imparipinnate and paripirnate.
Imparipinnate leaves are those that end in a leaf blade that does not have its own pair. An example of imparipinnate leaves would be the leaves of rowan, ash, and raspberry. Piripnately compound leaves are less common, but you still know some plants with such leaves. These are, for example, field peas, mouse peas and sweet peas.
Both simple and compound leaves of dicotyledonous and monocotyledonous plants are arranged on the stems in a certain order. The portions of the stem that bear leaves are called stem nodes, and the sections of the stem between the nodes are called internodes.
The arrangement of leaves on the stem is called leaf arrangement.
Most plants have alternate leaf arrangement, for example: rye, wheat, birch, apple tree, 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, and dead nettle are located on the stem not one at a time, but two at a time: one leaf opposite the other. This leaf arrangement is called opposite.
Sometimes there are plants with whorled leaves. Their leaves grow on the stem in bunches, whorls, arranged in three or more leaves per node, and form a kind of ring (whorl) around the stem. Among indoor plants, oleander has a whorled leaf arrangement, in an aquarium - elodea, among wild plants - northern bedstraw, lupine clover, four-leaf raven's eye and other herbaceous plants.
Various. At the same time, they have a lot in common. Most plants have green leaves.
The leaves consist of a leaf blade and a petiole (Fig. 123).
Leaf blade
The leaf blade performs the basic functions of a leaf.
petiole
At the bottom, the leaf blade turns into a petiole - the narrowed stem-like part of the leaf. With the help of a petiole, the leaf is attached to the stem. Such leaves are called petiolate. Petiolate leaves are found in linden, birch, cherry, maple, and apple.
Aloe, cloves, flax, tradescantia, and lungwort have leaves without 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, or small leaf-like dots (Fig. 124). The main function of stipules is to protect young developing leaves. In peas, spring cherry and many other plants, stipules remain throughout the life of the leaf and perform the function of photosynthesis. In linden, birch, and oak, filmy stipules fall off during the young leaf stage. In some plants, for example, in white acacia (Robinia pseudoacacia), the stipules are modified into spines and perform a protective function, protecting the plants from damage by animals.
The leaves of most plants range in size from 3 to 15 cm. The length of the leaves of some palm trees reaches 10 m or more. Floating rounded leaf blades with curved edges of Victoria regia, which lives in the waters of the Amazon River, reach 2 m in diameter. Such a leaf can easily hold a 3-year-old child on its surface. And in common heather, the leaf length is measured only a few millimeters.
Simple sheet
Linden, aspen, lilac, and wheat 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 and barley it is linear, etc. (Fig. 126).
The leaf blades of oak and maple are divided into lobes by cutouts and are called lobed (Fig. 127). Dandelion leaves are separate, their cuts are deeper. The cutouts of the dissected leaves of yarrow and wormwood reach almost to the middle of the leaf.
Complex sheet
Rowan, chestnut, acacia, strawberry, clover, and lupine have compound leaves (Fig. 128). They have several leaf blades, which are attached to one main petiole by small petioles. During leaf fall, complex leaves do not fall off entirely: first the leaves fall off, then the petioles.
The 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, and wheat, the veins are located parallel to one another. This is parallel, or linear, venation.
Arc venation
Kupena, lily of the valley, and plantain have arcuate venation—the veins run in arcs along the leaf.
Reticulate venation
In birch, oak, and fields, the veins on the leaves form a network. At the same time, lateral veins extend from the large central vein, which also branch. This venation is called reticulate. The reticulate veining can be finger-like or pinnate.
Palmate venation
With palmate venation, several large veins extend radially from the base of the plate, like splayed fingers (maple, etc.). Material from the site
Pinnate venation
With pinnate venation, one main vein is distinguished, from which branching lateral veins extend (birch, bird cherry, oak, poplar, etc.).
The leaves on the stem are arranged in such a way as to avoid shading one another.
Next leaf arrangement
Most often, a regular leaf arrangement is observed - the leaves on the stem are placed one after another (willow, oak, birch, cereals, blueberry, 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 per node, this is a whorled leaf arrangement (common loosestrife, bedstraw, crow's eye, oleander, elodea) (Fig. 131).
Leaf arrangement e - the order of placement of leaves on the shoot axis (Fig. 26). May be:
Leaf classification
There are simple and compound leaves. Leaves that have one blade (whole or notched) are called simple. Simple leaves withl
Rice. 27. Compound Leaves: 1 - trifoliate; 2 - finger-compound; 3 - odd-pinnate; 4 - pari-pinnate.
Compound Leaves- - leaves consisting of several clearly separated leaf blades (leaflets), each of which is attached with its petiole to a common petiole (rachis). Often a complex leaf falls off in parts: first the leaves, and then the petiole.
Depending on the location of the leaflets, they are distinguished (Fig. 27):
Pinnately leaves - leaves in which the leaflets are located on the sides of the rachis. When the apex of the rachis ends in one unpaired leaf, such leaves are called odd-pinnate(rose hips, white acacia). U paripirnate leaves, all leaves have a pair (peas, yellow acacia).
Palmate compound leaves - leaves in which the leaflets are not located along the length of the rachis, but only at its top in one plane (chestnut, lupine).
A special case of a complex worksheet is trifoliate leaf - a leaf with only three leaves (clover, oxalis).
The rachis of compound leaves can form lateral branches, then double-, triple-, quadruple-pinnate leaves appear. For example, mimosa has a double-pinnate leaf.
Leaf venation
Venation is a system of conducting bundles in leaf blades.
Rice. 28. Leaf venation:
1 - parallel; 2 - arc; 3 - mesh with a pinnate arrangement of the main veins; 4 - mesh with a finger-like arrangement of the main veins; 5 - dichotomous.
The nature of the arrangement of the veins and the shape of the leaf blades are closely interrelated (Fig. 28). There are:
simple venation- the leaf blade from the base to the apex is penetrated by only one vein (mosses, mosses);
dichotomous venation- the leaf blade is pierced by forked veins (ginkgo);
arc venation- the leaf blade from the base to the apex is pierced by several identical veins, arranged in an arcuate manner (lily of the valley, hellebore);
parallel venation- the leaf blade from base to apex is pierced by several identical veins arranged strictly parallel (rye, sedge);
reticulate venation- usually one vein enters the leaf blade from the petiole, which then gives off branches - lateral veins, forming a dense network. Reticulate venation can be pinnate or palmate.
Linden (Tilia) is a deciduous tree, including up to 45 species. It grows mainly in the temperate zone of the Northern Hemisphere. There are 7 wild species and 10 hybrids common in Russia. Small-leaved and heart-shaped linden are more common. In Ukraine and Moldova, mainly European, large-leaved, felt, and Hungarian linden grows. In the Caucasus and Crimea - Crimean, Caucasian, pubescent columnar. Amur, Korean, Chinese, spreading, and Manchurian linden are common in the Far East. In Tatarstan, Mordovia and Chuvashia, pure linden groves (lime forests) have been formed. The maximum age of linden forests is 400 years. In single plantings, the tree can live up to 1200 years. On city streets, 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 and depends 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 ponds.
The most popular is the small-leaved linden, used in medicine and the national economy. A species very close to it grows in Western Siberia - the Siberian linden.
The linden tree is a source of a pleasant, strong aroma, as well as an effective remedy in the fight against colds.
Trunk, bark and stem of linden
In forest stands, trees have a straight trunk, highly cleared of branches, and a highly raised, thin crown. In open plantings the crown is denser and located lower. The lower branches of the linden tree extend from the trunk and rise, the middle branches extend horizontally from the trunk, and the upper ones rise upward at an angle. The foliage of the tree is dark green, with drooping yellow-white flowers - semi-umbels and yellow-green bracts. The crown shape is tent-shaped. Complete crown formation ends at the age of 40 years.
The bark of young linden is smooth, light gray; in adults it is thick, dark gray, covered with deep grooves and cracks.
The linden stem has a structure typical of all trees. In its center there are thin-walled core cells where nutrients accumulate. The core is surrounded by a thick layer of wood, which makes up 90% of the total volume of the stem.
This plant is a diffuse-vascular, mature woody, kernel-free species. It has soft wood of a white, pink, or reddish hue. It has a blurred, inexpressive texture, so the annual layers on sections can be traced rather poorly. On a transverse section, narrow heart-shaped rays in the form of thin lines are visible; on a radial section, dull stripes and blurry dark spots can be seen. Late wood is no different in density from early wood. There are 4.5 annual layers per 1 cm cross section. The vessels are thin and invisible. The structure of the wood is homogeneous. Humidity is distributed evenly over the cross section of the trunk.
Leaf arrangement and linden leaf
The linden leaf is simple, heart-shaped, pointed, the edges are finely toothed, with large veins, dark green above, light green below, with reddish hairs. It is supported by a reddish petiole 1-3 cm long.
It contains calcium, so when it falls it quickly decomposes, thereby improving the properties of the soil and increasing its fertility.
Over 1 year, the mass of dry linden leaves during decomposition decreases by 70% of the original mass.
Moreover, intensive decomposition occurs in the spring-summer period, which is most favorable for the development of microorganisms in the soil. Freshly fallen leaves contain ash, potassium, calcium, nitrogen, and sulfur.
Linden buds and root
Linden buds are reddish-brown, smooth, covered with scales, ovoid in shape, arranged in two rows. Length 6-7 mm, width 3-5 mm. Each bud contains 5 leaves with stipules and two rudimentary leaves. The shoots are brown-brown, covered with lentils.
The root system of the plant on fertile, fresh, loose soils is powerful, highly developed, has a tiered structure, and uses nutrients from all layers of the soil. The linden root goes deep into the ground and gives off well-developed lateral roots. Linden also has a superficial root system formed by adventitious roots.
The flowers are bisexual, small, regular in shape, collected in racemes (umbrellas), have 5 sepals, a corolla with 5 petals, a pistil and several stamens. Flowering begins in June and lasts until mid-July. Flowering duration is up to 14 days. The tree begins to bloom at 20-25 years of age.
Flowering and nectar production depend on the plant’s habitat, geographic, environmental and other factors. However, it has been noticed that the linden begins to bloom when the bees have the maximum opportunity to use nectar. Nectar in linden flowers is secreted by nectar-bearing tissue and is retained inside the sepals. The released nectar is not reabsorbed.
Linden branch and seeds
The period of tree maturation begins at the age of 20-30 years. The linden branch becomes strong enough to ensure flowering and seed ripening.
At this age, a large number of inflorescences appear. Linden seeds ripen in autumn.
Spread by wind, animals and birds. They are especially noticeable on snow crust. They are collected from October to March.
The fruit is a spherical, elongated nut containing 1, 2, rarely 3 seeds. The fruit shell is dense and waterproof.
Features of linden
The plant is quite shade tolerant. On this basis it is second only to coniferous species, beech and oak. A shade-tolerant linden tree with a wide spreading crown often shades the soil for other plants. Frost-resistant. Among broad-leaved trees, it penetrates farthest to the north, growing in harsh conditions at very low temperatures. It is not afraid of frosts, as it blooms late. Resistance to frost is explained by the short period of shoot growth, the high ability to retain water in the leaves, as well as the high oil content in the branches. Linden fats contain unsaturated linolenic acid, which quickly oxidizes and generates heat, so in winter linden can withstand temperatures down to -50°C.
Sometimes frost cracks form on the south side of the trunk and branches of the tree. This is due to the sharp temperature change. 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 if there is excessive drought, growth decreases. The mosaic arrangement of linden leaves protects from strong sun and dry climate, 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 and is smoke resistant. On fertile soils, its gas resistance increases. The most unpretentious species of this plant is considered to be small-leaved linden. It can grow in different soils, except swampy, excessively salty and dry. Prefers loose, humus-rich areas.
Linden trees growing in the zone of podzolic soils indicate high soil fertility in this area. In the forest-steppe zone, the presence of linden indicates 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, pine needles, fallen branches and bark forms neutral humus containing ash elements that reduce the acidity of the soil and increase the degree of its saturation.
After cutting down a tree, stump growth forms. It appears around the neck of the root and begins to germinate profusely. The property of linden is to produce dense growth and continues until old age. At age 100, this ability begins to decline. After clear cutting, linden shoots begin to densely populate the cutting area, suppressing self-seeding and slowing down the growth of conifers.
Linden tolerates pruning well, so its crown can be given any shape. This tree is often used to create parks, squares and alleys.
23. Look at the drawing. Label what kind of leaves these are according to the method of attachment and stem and what their parts are
Petiolate leaf:
1 - leaf blade
2 - petiole
3 - stipules
Leaf sessile:
1 - leaf blade
4 - base of the leaf blade (leaf sheath)
24. Look at the drawing. Write down separately the numbers that indicate simple and complex leaves
Simple - 1, 4, 6, 8
Difficult - 2, 3, 5, 7
25. Look at the drawing. Determine what type of venation these leaves have
Mesh. Parallel. Dugovoe
26. Complete the laboratory work “Simple and compound leaves, their veining and leaf arrangement”, fill out the table
27. Think about whether it is possible to determine only by the veining of the leaves whether this plant is a monocot or a dicotyledon. Give a reasoned answer
Not really. Parallel and arcuate venation is characteristic mainly of monocots, with the exception of the crow's eye, which has a reticulate venation. Dicotyledons most often have reticulate venation, but there are exceptions, for example, plantain with arcuate venation