BOTANY. PLANT MORPHOLOGY - O. A. Shevchuk - 2014

MAIN DIRECTIONS OF MORPHOLOGICAL EVOLUTION

Depending on their level of Organization, existing plant species are generally divided into two major groups: higher and lower plants.

In lower plants, which are thalloid or thallophytes (Thallobionta), the body is not differentiated into roots, stems, and leaves, and complex tissue structures are also absent. Primitive forms consist of a single Cell. The reproductive Organs of lower plants are gametangia.

In higher plants (most mosses (Bryophyta), clubmosses (Lycopodiophyta), horsetails (Equisetophyta), ferns (Polypodiophyta), gymnosperms (Pinophyta), and flowering plants (Magnoliophyta)), the body is differentiated into vegetative organs—leaf-stem shoots and roots—as well as Generative organs. They consist of various Tissues.

The transition of organisms to land was one of the primary factors driving the accelerated differentiation and evolution of plants. In an aquatic environment, all parts of a plant body exist under approximately uniform conditions regarding Water, air, and light supply. Consequently, they perform identical Functions and share the same Structure. On land, a plant is exposed to a greater variety of factors. Terrestrial plants experience water scarcity, as a more or less constant supply of water is available only in the soil. Under such conditions, plants whose bodies are partially located in the soil are relatively better adapted and predominantly survive. Therefore, in The process of adapting to terrestrial life, higher plants developed a division into above-ground and underground parts. The underground parts lost their photosynthetic capacity and serve to absorb water, thus providing soil Nutrition. In modern higher plants, such underground organs are roots. They anchor the plant in the soil and absorb water and mineral nutrients. The habitat and functions leave a distinctive mark on both the external and Internal Structure of the ROOT.

The above-ground PARTS OF THE body—shoots—carry out Photosynthesis, where organic substances are produced and accumulated. Shoots provide aerial nutrition for the plant. An exchange of energy, organic, and Mineral Substances occurs between the above-ground and underground organs. Due to the increased outflow of these substances, the above-ground organs differentiate into stems and leaves. Leaves are the organs of photosynthesis, characterized by a large external surface area that facilitates gas exchange.

Stems act as intermediaries between leaves and roots. They ensure the Transport of substances from leaves to roots and vice versa. Through the stem, leaves are positioned most favorably with respect to light. The increase in the contact area with the external environment occurs As a result of the elongation and branching of the plant Organism.

Unicellular plant organisms lost their mobility and transitioned to a sessile lifestyle. The absence of motile forms in the vegetative state, linear growth, branching, and a sessile lifestyle gave rise to another characteristic feature of plants: the capacity for unlimited growth.

In lower plants, body differentiation proceeded in three directions:

1) without a significant increase in the size of the unicellular plant organism;

2) an increase in the size of the organism occurred, yet it remained unicellular. In this case, the Cells contained A large number of nuclei and other Organelles. These are non-cellular organisms, and their shapes vary;

3) Multicellular Organisms emerged, in which heterogeneous structures with distinct functions developed.

It should be noted that colonial forms occupy an intermediate position between multicellular and unicellular organisms; in these forms, cells do not separate after division but remain interconnected.

Physiologically and morphologically distinct parts within The system of an integral organism are called plant organs. Plant organs evolved over the course of evolution. Primary primitive lower plants (Algae, Fungi, Lichens, liverworts) do not yet form organs; their body is represented by a thallus. Consequently, such plants are referred to as thalloid plants.

In higher plants, There are two groups of organs: vegetative and generative. Vegetative organs include the root and the SHOOT. A shoot consists of the stem, buds, and leaves. Vegetative organs perform nutritional functions and ensure the individual Development of Plants.

In flowering plants, the generative organs are the flower, seed, and fruit. These organs ensure the Sexual reproduction of plants.

There is a close connection and interdependence between vegetative and generative organs. The activity of vegetative organs leads to the accumulation of organic substances, which are a prerequisite for The formation of generative organs. In turn, The Development of generative organs results in the formation of an embryo from which the Vegetative organs of the next generation develop.

The root and stem are axial organs that constitute a single plant axis with opposite poles. Leaves and generative organs—flowers—develop symmetrically as lateral appendages along this axis.

Organs consist of tissues, and tissues, in turn, consist of cells. Vegetative and generative organs are formed at the plant's growth points. Their development is based on Cell Division and Cell Differentiation processes.

Vegetative organs first appeared in the earliest land plants, the Rhyniophytes. Rhyniophytes did not form leaves and roots; their body consisted of leafless underground and above-ground axes, known as telomes. In extinct clubmosses (Lepidodendrons), enations or phylloids appeared on the aerial telomes. Phylloids were leaf-like formations, or enations, originating as outgrowths of the outer layers of the cortical parenchyma. They were not true leaves, yet they shared a common origin with the stem. Thus, it can be hypothesized that the shoot appeared first in The structure of vegetative organs.

The plant root evolved as a result of the morphological and functional differentiation of rhizomoids. These were telome-like branches used by fossil plants to anchor themselves in the soil. Rhizomoids bore rhizoids, through which the plants absorbed water and mineral salts.