Most leaves of seed plants consist of morphologically different parts: leaf blade and petiole, sometimes stipules. What is a petiole and is its presence necessary, what tasks does it perform? More on this below.
The main functions of the petiole
A thin elongated petiole part 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.
The change in turgor pressure in the cells of different parts of the petiole leads to the fact that it orientates the leaf in the most favorable position with respect to the flow of light. Thanks 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. Conducting tissues here are represented by bundles of xylem and phloem and do not form a sharp transition. Through them, water and mineral salts enter the leaf tissue, and a solution of carbohydrates synthesized during the photosynthetic activity of the parenchyma is removed.
In complex leaf blades, there are two levels of attachment:
- A precast leaf is attached to the shoot with a rachis petiole.
- Each individual leaf blade has its own petiole of the second order, called the petiole, which is attached to the rachis.
The leaf may also be dehisan. In such cases, its base grows and adjoins the shoot almost along its entire perimeter (at the vaginal leaves) or at one point (sessile leaf).
Are there fruit stalks?
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 stalk. Until the pollination of the flower from which the fruit evolved, this structure was a pedicel.
It is clear that such a petiole provides nutrition to the tissues of the ovary. While the fruit or berry grows, sugar and starch are synthesized in their cells, synthesized in the tissues of the leaves of the plant during photosynthesis.
The peduncle transforms over time, becomes thicker, and in some plants it becomes lignified. This is necessary to hold the poured fruit, because it is much heavier than a flower.
Regardless of the type of plant, the leaf petiole performs a conductive and mechanical function. It provides the attachment of the plant organ to the stem and the holding of water and organic substances.