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

IX. LOWER VASCULAR PLANTS

Vascular plants are multicellular, eukaryotic, phototrophic organisms whose vegetative body is differentiated into Organs and Tissues. Their reproductive organs are multicellular, and their life cycle features the alternation of two generations: the asexual (sporophyte) and the sexual (gametophyte).

The vegetative body of most vascular plants is represented by shoots and roots. However, thalloid forms also occur among them, particularly in gametophytes. The sporophyte represents a more advanced form of the vegetative body.

A distinctive feature of vascular plants is the presence of conducting, mechanical, epidermal, fundamental, meristematic, and Secretory Tissues, which, along with their morphological differentiation, are the result of ADAPTATION TO A terrestrial lifestyle.

According to their method of reproduction and species dispersal, vascular plants are divided into lower vascular (spore-bearing) plants and seed plants.

The organs of Sexual reproduction in lower vascular plants—the antheridium and the archegonium—are formed on the gametophytes and are multicellular. The antheridium is a sac-shaped male reproductive organ. Externally, antheridia are covered by a single-layered Cell wall, beneath which lie spermatogenic Cells that undergo mitosis to form spermatozoa.

The archegonium is a flask-shaped female reproductive organ. Externally, it is covered by a single-layered cell wall and consists of two parts: a lower, expanded venter and an upper, narrowed neck containing a canal. The venter produces the egg cell and a ventral canal cell, while the neck contains neck canal cells. By the time the egg cell matures, the canal cells mucilaginously dissolve, and the mucus is pushed outward, attracting spermatozoa that swim through Water to the archegonium and fertilize the egg cell within it. Fertilization in lower vascular plants requires water.

Sexual reproduction is a factor in one of the forms of genotypic Variability—combinative variability. A multicellular diploid sporophyte develops from the diploid zygote through mitotic division. It bears a sporangium with a multicellular wall and sporogenous tissue (the archesporium), which consists of spore mother cells. Each of these cells undergoes Meiosis to form four haploid spores, which are shed from the sporangium upon maturation.

A spore is a single cell typically covered by two walls: the exine (outer) and the intine (inner). Under favorable conditions, the spore

cell undergoes mitosis and develops into a multicellular haploid gametophyte.

It is precisely through spores that lower vascular plants increase the number of individuals, meaning reproduction takes place. Spores are disseminated by abiotic or biotic factors, facilitating the spread of plants across the globe.

Lower vascular plants are divided into seven divisions: Rhyniophyta, Zosterophyllophyta, Bryophyta, Lycopodiophyta, Psilotophyta, Equisetophyta, and Polypodiophyta.