Plant leaf. External structure. Types of leaf arrangement and leaf venation

The leaf is part of the shoot. It carries out three main functions – photosynthesis (the formation of organic matter), gas exchange and water evaporation.

Parts of a plant leaf.
The leaf has a leaf blade, petiole, base and stipules. The leaf blade is the main site in which photosynthesis takes place. The petiole attaches it to the stem and turns it into the best position in relation to the light.

Leaves with petioles are called petiolate. Leaves without petioles are called sessile.
Example: petiole leaves – in nettle, linden, maple, birch, apple, cherry, etc.

Sessile leaves – in dandelion, aloe, flax, chicory, wheat, etc.

Plant leaf shape.
Leaves are round, oval, cordate, acicular, etc. in shape. The leaves are also varied in shape of the edge of the plate.

Example: for example, a leaf of an apple tree has a jagged edge, an aspen has a serrated edge, a lilac has an entire edge.

Leaves are simple and complex
Simple leaves consist of one leaf blade.
Example: such leaves are found in birch, maple, oak, bird cherry and other plants.

Composite leaves consist of several leaf blades connected to a common petiole by small petioles.
Example: ash, mountain ash and many others have such leaves.

Leaf vein
When studying the external structure of the leaf, it is clearly seen that the veins are clearly expressed on the leaf blade of many plants.
They are represented by bundles of conductive and mechanical tissue. Water and mineral salts enter the leaf along the veins and the organic matter formed in the leaf is removed.

To determine the type of plant according to a special identifier, one must be able to distinguish between leaf venation and its location on the stem.

The types of leaf venation are arcuate, parallel, reticulate (or pinnate), fingerlike.

Arcuate venation. Plantain and lily of the valley leaves have large veins and, in addition to the central one, are curved like an arc. Their venation is called arcuate.

Parallel venation. If several large veins run parallel to each other along the plate, then the venation is called parallel. Leaves of wheat, corn, millet have such venation.

Reticulated (pinnate) venation. Oak and birch leaves have one powerful vein located in the middle. This is the main vein, around which branched small veins create a net. This venation is called reticular. Since veins extend to the left and right from the main vein, resembling the structure of a feather, such venation is also called cirrus, or cirro-reticulate.

Finger (finger-mesh) venation. The leaves of the sycamore maple, caustic buttercup have several large, almost identical veins, fanning out from the base of the plate. They also branch many times. This venation is called finger, or finger-mesh.

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