MORPHOLOGY OF PLANT VEGETATIVE ORGANS

1. Plant Vegetative Organs. General Structural Patterns

As plants transitioned to land during evolution, their uniform thallus differentiated into Organs, and organs into Tissues. Changing environmental conditions driven by profound climate shifts served as the primary driving force behind the adaptive specialization of plants.

An organ is a part of an Organism that possesses a definite Structure and performs specific Functions. Higher plant organs are divided into vegetative and generative (reproductive). Vegetative organs include the ROOT and SHOOT, while Generative organs include the flower, seed, and fruit.

General patterns in The structure of morphological formations can be distinguished.

Polarity refers to the differences between opposite points (poles) of a plant organism or organ. Each organ has two poles: the upper (terminal or apical) and the lower (basal).

Symmetry is the spatial arrangement of an organ's parts such that a plane of symmetry divides the object into mirror-image halves. Symmetry determines the regular arrangement of an organ's parts relative to the axis, particularly the arrangement of leaves on the stem. Organs are classified as asymmetric, monosymmetric, or polysymmetric.

Asymmetric organs are those through which not a single longitudinal plane of symmetry can be passed (for example, the leaf of an elm or the flower of a canna).

Monosymmetric, or bilateral (bilaterally symmetrical), organs are those through which only one plane of symmetry can be passed (the leaf of a lilac or poplar, the flower of a pea or sage).

Polysymmetric, or radial, organs are those through which two or more planes of symmetry can be passed (stems with opposite leaf arrangement, root crops, the flower of a tulip).

Vertically oriented organs are termed orthotropic. These include upright stems and vertically growing taproots. Organs

positioned in a horizontal plane, parallel to the soil surface, are referred to as plagiotropic.