Mechanical conductive and core fabrics presentation. Mechanical fabric. Photosynthetic leaf tissue

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Conducting tissues are called xylem and phloem. They form a continuous conducting system in the plant body, which permeates the vegetative and generative organs of plants.

Both tissues perform a conductive function.

Xylem is the tissue of vascular plants that conducts water and dissolved minerals.

Phloem is a tissue that conducts organic substances formed in leaves during photosynthesis.

Conductive tissues are classified according to their origin and time of occurrence in the plant body (ontogenetically).

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Based on their origin, tissues arising from the primary vascular lateral meristem - the procambium - are called primary, and those arising from the secondary meristem - the cambium - are called secondary.

• Procambium primary
• primary phloem
• xylem
• protophloem
• metaphloem
• protoxylem
• metaxylem
• Cambium secondary phloem (phloem)
• secondary xylem (wood)

Conductive tissues differ ontogenetically in the time of their appearance. The elements of primary phloem and primary xylem that emerged first are called protoelements (protophloem, protoxylem). Later, metaelements (metaphloem, metaxylem) appear.

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general characteristics

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In monocotyledonous plants (cereals, lilies, sedges, orchids, etc.), which do not have secondary growth, metaxylem and metaphloem constitute the entire conductive tissue of an adult plant and function throughout the life of the plant. Since the cambium is absent in monocots, secondary xylem and phloem are not formed. All conductive tissue is formed from procambium.

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Common features of Ks and Fl

• Identical in origin, because both tissues arise from the procambium and cambium;
• Both tissues perform a conductive function;
• There are common features in the structure. Ks and Fl consist of different types of cells, therefore they are complex tissues. They include parenchyma cells and conducting elements.
• Cells in secondary tissues are arranged in a specific manner, forming an axial (longitudinal or vertical) system and a radial (transverse or horizontal) system.
• The axial system consists of rows of cells, the long axes of which are oriented in the stem and root parallel to the main axis of the stem and root.
• The radial system consists of rows of cells oriented perpendicular to the axes of the stem and root.

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Main cell types

• Xylem
• Phloem
• Axle system
• Axle system
• Function
• Function of the tracheid
• vessels
• holding water
• sieve tubes
• sieve cells
• conducting organic matter
• fibers (fibrous tracheid, libriform, septate fiber),
• sclerenchyma bast fibers,
• sclereids,
• resin passages, mechanical, storage
• parenchyma cells
• parenchyma cells
• living cells,
• storing
• Beam system
• Beam system
• parenchyma cells
• parenchyma cells are uniseriate or multirowed
• living cells,
• storing
• tracheids in conifers
• holding water
• differences

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Histological composition of Cs, structure and functions of conductive elements

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Tracheids

Tracheids have a length of 1-4 mm, in cross section from 0.1 to 0.01 mm. These are individual cells with uneven thickenings in the membrane. The longitudinal walls usually thicken. Each tracheid is isolated and has its own shell. Tracheids are imperforate cells.

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Perforations and pores

• Perforations are through holes on the transverse walls that form only near vessels (tracheas). in tracheids, pores form on the longitudinal walls.
• Pores are non-thickened areas of the secondary shell, which can be simple or bordered.

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Types of tracheid thickenings

The thickening of the longitudinal walls can be different. The secondary shell of tracheids can have the shape of rings not connected to each other (ringed tracheids), or the shape of a spiral (spiral tracheids). If thickenings are formed in the shape of a spiral, the turns of which are interconnected, such thickenings are called ladder thickenings. Reticular thickening in the form of a network, a porous thickening often with bordered pores.

a – ring-spiral, b – spiral, c – porous

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Microphotographs of thickening of blood vessels

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Microphotograph and three-dimensional image of secondary xylem:

• 1 – libriform,
• 2 – vessels, 3 – tracheids, 4 – vertical parenchyma,
• 5 – horizontal parenchyma (core ray)

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Ontogenesis of tracheids

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Evolution of tracheids

• a1-a4 – evolution of fibers;
• b1-b4 – evolution of vascular segments;
• I-III – long tracheids from primitive woods

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Trachea

• A vessel is a group of tracheids in which the transverse partitions disappear. The vessel consists of many cells called the vessel segment, which form a vertical row.
• Along the segments of the vessel, water moves through the perforations, and the perforated part of the shell of the vessel segment is called the perforation plate.

Diagram of the structure and combination of tracheids (1) and vessel segments (2).

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• The plate can be simple or complex.
• A complex plate can be:
• Staircase.
• Mesh.

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Trachea

The vessels also have pores on their longitudinal walls. They can be simple or bordered, like tracheids. In vessels, the number and nature of the distribution of pores varies and the following types of pores are distinguished:

• Ladder - pores are simple, elongated.
• Transitional - simple pores alternate with bordered ones.
• Opposite - bordered pores are located opposite.
• The next one is that the bordered pores are arranged in rows, the most highly organized type.

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A – annular, B – stretched-annular, C – annular-spiral, D, E – spiral, E – reticular, G – scalariform, H – opposite-pore

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• Thus, pores in vessels are formed on both transverse and longitudinal walls. The shells are lignified (lignified).
• In a mature state, vessels, like tracheids, are dead cells, because perform the function of conducting water and substances dissolved in them.
• Ontogenesis proceeds in the same way as in tracheids.
• The vessels do not have a specific length; it can be from 60 cm to 4.5 m.

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Development of vascular segments with spiral thickening

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The evolution of blood vessels followed the following pattern:

1. Shortening of the vessel segment

2. Expansion of the vessel diameter

3. Reducing the inclination of the end parts to horizontal

4. The number of perforations is reduced from 20 to 1

5. Another porosity of the T.O. appears.

The vessel was adapted for better water conduction

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Phloem - histological composition and functions of conducting elements.

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• The conducting elements of phloem are sieve cells and sieve tubes.
• Sieve cells are less specialized elements found in ferns and gymnosperms.

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Sieve tubes are highly specialized conductive elements characteristic of angiosperms.

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• The sieve area is a specialized area of ​​the cell wall penetrated by openings (tubules). Through the sieve fields, the sieve elements communicate with each other.
• Sieve cells and sieve tubes have thick membranes. In sieve cells, sieve fields are located only on the longitudinal walls, the openings are small.