Tracheophyte size was only possible due to adaptations that made possible the support of the living organism and the availability and transport of water to all cells.
The support of a tracheophyte is due to the existence of specialized tissues for this function: the collenchyma it's the sclerenchyma, which we'll see next.
The collenchyma cells are elongated, irregular and arranged in the form of bundles. When cut transversely, they look varied. They are alive, nucleated, and the wall has more intense cellulose reinforcements in the inner corners of the cell, giving some resistance to lateral crushing.
The collenchyma is a flexible fabric, located more externally in the body of the plant and found in young structures such as leaf petiole, stem end, roots, fruits and flowers.
The sclerenchyma is a stiffer tissue than the collenchyma, found in different places on the body of a plant. Sclerenchyma cells have secondary wall thickening due to impregnation of lignin. The most common sclerenchyma cells are the fibers and the sclerids, also called sclerites.
Inner structure of the leaves
The leaf is completely covered by the epidermis, and its interior, called mesophyll (from the Greek, mesos, middle and phylon, leaf), consists of chlorophyll parenchyma, conductive tissues and supporting tissues.
Leaf chlorophyll parenchyma can generally be of two types:
- palisadic - consisting of prismatic cells juxtaposed as a stockade, and
- lacunous It consists of irregularly shaped cells that leave spaces or gaps between them.
There may be palisade parenchyma next to the epidermis of both sides of the leaf, or, as is more common, palisade parenchyma next to the epidermis of the upper and lacunous next to the bottom.
The conductive tissues present in the leaf are grouped in woody bundles, in which the xylem is facing the upper epidermis and the phloem, the lower epidermis. The thicker conductor bundles form the leaf veins, visible to the naked eye.