BOTANY WITH BASICS OF HYDROBOTANY (AQUATIC PLANTS OF UKRAINE) - B.Ye. Yakubenko - 2011

VIII. BASICS OF PLANT MORPHOLOGY AND ANATOMY

Morphology and Anatomy of the Leaf

Functions of the Leaf

It performs three main Functions: Photosynthesis, Transpiration, and gas exchange.

Along with this, the leaf can serve as an organ of vegetative propagation (begonia, violets), act as a storage site for nutrients, Water, and mineral salts, function as a trapping apparatus (Insectivorous Plants such as sundew, bladderwort, butterwort), serve as a climbing organ (vetch, pea), and provide plant protection (spines in cacti, astragalus).

During ontogenesis, the leaf develops as a lateral outgrowth of the SHOOT apex. It initiates as an oval bump, the Cells of which initially divide in three directions, and subsequently in two. Under such conditions, the leaf primordium becomes flattened.

Initially, the leaf is not differentiated into upper and lower parts. This division occurs later, when its apex grows more intensively than the base. However, this apical growth is short-lived; the leaf continues to grow longer at the base due to intercalary meristem.

The upper part of the leaf primordium differentiates into the leaf blade and petiole, while the lower part develops into the leaf base and stipules (Fig. 72). Under these conditions, the leaf blade develops quite uniformly at first, followed by the petiole.

A leaf that possesses both a leaf blade and a petiole is called petiolate. It attaches to the stem by means of the petiole. If the latter broadens and partially or fully embraces the stem, it is called a leaf sheath (cereals). In the leaves of grasses, the Base of the leaf blade is elongated at the edges to form auricles (fescue, timothy, foxtail, bentgrass). At the junction of the sheath and the leaf blade, a ligule appears, which protects the stem and its intercalary meristem from the penetration of water and pests. In sedges, leaves are ligueless—they do not form a ligule, which is why they are referred to as leaves with a closed sheath.

Leaves that lack a petiole and attach to the stem by their base or grow from it are called sessile. If they embrace the stem with their base, they are termed amplexicaul (clasping). Occasionally, perfoliate leaves occur (silphium), in which the stem appears to pierce through the leaf. If the expanded stipules embrace the stem, they form an ochrea (ocrea). This phenomenon is characteristic of buckwheat, sorrel, rhubarb, knotweed, and others.