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

X. SEED PLANTS

Seed plants are higher plants in which the sporophyte is dominant over the gametophyte, and the gametophyte develops directly on the sporophyte. Unlike spore plants, seed plants reproduce and spread through seeds, which develop from ovules.

These plants are heterosporous. Microsporogenesis takes place in microsporangia, which form on microsporophylls. Inside the microsporangia, archesporial Cells undergo Meiosis to produce microspores, which then develop into the male gametophyte—the pollen grain.

Megasporogenesis occurs within ovules consisting of a nucellus surrounded by an integument. An archesporial Cell in the nucellus undergoes meiosis to form a megaspore, which germinates inside the ovule into the female gametophyte. The male Gametes, or sperms, are non-flagellated. The Fertilization process is siphonogamy: the sperm cells travel through a pollen tube to reach the egg cell within the female gametophyte, where fertilization takes place. The zygote develops into the sporophyte embryo, and the ovule matures into a seed.

Unlike typically unicellular spores, a seed is a multicellular Structure. It consists of three main parts: an embryo equipped with the rudiments of all Water/115.html">Vegetative Organs of the sporophyte; a multicellular tissue storing reserve nutrients; and a multi-layered seed coat.

Major evolutionary advancements in seed plants—specifically the retention of the gametophyte on the sporophyte, siphonogamous fertilization, and The Emergence of the seed as an organ for reproduction and dispersal—gave these plants a significant adaptive advantage. Thanks to these acquired traits, they began to outcompete spore plants and established dominance in the flora of the Earth.

Seed plants comprise two divisions: gymnosperms (Pinophyta) and angiosperms (Magnoliophyta).