Most leaves of seed plants consist of morphologically distinct parts: lamina and petiole, sometimes stipules. What is a petiole and is its presence necessary, what tasks does it perform? More on this below.
Basic functions of the petiole
The thin elongated petiole of the leaf secures it to the stem. During the growing season of the plant, the connection between the petiole and the stem is strong. At the end of the season in deciduous forms, when the leaf accumulates metabolic products, the petiole breaks off, freeing the plant from ballast.
Change in turgor pressure in the cells of different parts of the petiole leads to the fact that it orients the leaf in the most favorable position in relation to the light flow. Due to the movement of the leaves, a leaf mosaic is formed.
The anatomical structure of this part of the leaf is such that the petiole is a continuation of the central vein. Conductive tissues here are represented by bundles of xylem and phloem and do not form a sharp transition. Through them, water and mineral s alts enter the leaf tissue, and a solution of carbohydrates is removed,synthesized during the photosynthetic activity of the parenchyma.
In complex leaf blades, two levels of attachment are distinguished:
- The assembly leaf is attached to the shoot with the help of a rachis petiole.
- Each individual leaf blade has its own second-order petiole, called the petiole, which is attached to the rachis.
The leaf can be without stems. In such cases, its base grows and adjoins the shoot along almost its entire perimeter (near the vaginal leaves) or at one point (sessile leaf).
Do fruit petioles exist
What is the origin of the petiole of berries or fruits? A dense stem, with which cherries, apricots, apples are attached to the branches, is called a peduncle. Until the moment of pollination of the flower from which the fruit developed, this structure was a pedicel.
It is clear that such a petiole provides nutrition to the tissues of the ovary. While a fruit or berry is growing, sugars and starches synthesized in the tissues of the leaves of the plant during photosynthesis enter their cells.
The stalk transforms over time, becomes thicker, and in some plants becomes woody. This is necessary to hold the pouring fruit, because it is much heavier than the flower.
Regardless of the type of plant, the leaf petiole performs a conductive and mechanical function. It provides attachment of the plant organ to the stem and conduction of water and organic matter.
