Other structural features of plant stems:
1, epidermis: the first layer is living cells. It includes epidermal cells and stomata. The outer wall of epidermal cells often has epidermis and stratum corneum. Belongs to a conservation organization.
2. Cortex: It is located inside the epidermis and consists of multiple layers of cells.
(1) Thick horny tissue: It exists in bundles or sheets and plays a supporting role. Often contain chloroplasts, so young stems are often green and have photosynthesis.
(2) parenchyma cell: It consists of multiple layers of parenchyma cells with gaps between them, and the outer cells contain chlorophyll. There are often some secretory structures in parenchyma of cortex. In addition, it also has the functions of ventilation and storage.
(3) Endodermis (starch sheath): The innermost cells of cortex often contain starch granules, so it is also called starch sheath (only found in some plants).
3. stele (vascular column): the part in the cortex, without stele sheath or inconspicuous. It consists of vascular bundle, medulla and medullary rays.
(1) vascular bundle: mostly infinite collateral vascular bundle, consisting of the following parts:
Primary phloem: It consists of sieve tube, companion cell, phloem fiber and phloem parenchyma cell.
Vascular cambium: located between phloem and xylem.
C. Primary xylem: It consists of vessels, tracheids, wood fibers and wood parenchyma cells. The mature mode is internal startup.
D, some plant vascular bundles are double tough vascular bundles, that is, there is an endogenous phloem inside the primary xylem.
The vascular bundles of the stem are arranged in a discontinuous ring on the inner side of the cortex.
(2) Myeloid ray: It consists of parenchyma cells between two adjacent vascular bundles. It has the functions of storage and radial transportation, and some myeloid ray cells can be transformed into fascicular cambium.
(3) pith: located in the middle of young stem, composed of large parenchyma cells. Large volume, often containing starch granules, with storage function. The medullary cells of a few plant stems are destroyed, forming a hollow medullary cavity.
Function: Stem is the main channel for transporting substances in plants; Normal stems grow on the ground, the lower part is connected with roots, and the upper part supports leaves, flowers and fruits, so the main functions of stem-ground transportation and mechanical support are; The stem also has the function of storage and reproduction. Light green stems can also carry out photosynthesis.