Plant Tissues: Classification and Functions in Adult Organisms

Adult Tissues

Adult tissues originate from meristems, and their cells have lost the ability to multiply and differentiate. Depending on the function they perform, they are classified as fundamental, supportive, driver, guard, and secretory tissues.

1. Fundamental Tissues

These tissues are responsible for the nutrition of the plant, as they are involved in photosynthesis, respiration, and the storage of reserves. Types include:

• Parenchyma Chlorophyll: Its cells contain many chloroplasts, making it responsible for conducting photosynthesis. It is found in the green parts of the plant, such as leaves and herbaceous stems.
• Reserve Parenchyma: Its cells accumulate reserve substances like starch, fats, and proteins. It contains no chloroplasts and is located in the stems, roots, and seeds.
• Parenchyma Aquifer: Found in arid environments, this is a specialization for plants adapted to media with low humidity, like cacti. The leaves have parenchymal cells with large vacuoles that store a large amount of water.
• Aerifero Parenchyma: The cells that compose it are well spaced to store air and promote circulation. It is typical of aquatic plants, serving as an air flotation system.

2. Supportive Tissues

Their primary function is to provide consistency and rigidity to the plant. Their cell walls are very thick and sometimes reinforced with lignin. There are two kinds of supportive tissue:

Collenchyma

This serves as supporting tissue for the growing organism. Its cells are alive, resilient, and extensible. As they age, the cell walls lose elasticity, so this tissue becomes more fragile and hard in parts of the plant that will no longer grow. It is generally located below the epidermis of herbaceous stems.

Sclerenchyma

This serves as supporting tissue in adult organs that have stopped growing. It consists of dead cells whose walls are thickened and lignified. It includes:

Fibers

Elongated cells with pointed ends, occurring scattered or in groups in the roots, stems, leaves, and fruit.

Fibers of Xylem

Fibers are arranged in long rows in woody stems, forming part of the conducting tissue.

Sclereids

Short and very lignified cells that may appear scattered, as in the pulp of the fruit, or layered to form the solid "bones" of the fruits.