**History and Evolution of Seeds**:
– First land plants evolved around 468 million years ago.
– Gymnosperms, the first seed-bearing plants, appeared during the late Devonian period.
– Seed ferns evolved during the Carboniferous period.
– Seed formation is crucial in the reproduction of seed plants.
– Seed plants dominate land ecosystems, from forests to grasslands.
**Seed Development**:
– Seed development stages: Zygote, Proembryo, Globular, Heart, Torpedo, Mature Embryo.
– Angiosperm seeds are enclosed in fruits for protection.
– Gymnosperms develop seeds naked on cone bracts.
– Angiosperm seeds consist of embryo, endosperm, and seed coat.
– Seed development in angiosperms starts with double fertilization.
**Structure of Ovule and Embryo**:
– Ovule components: funicle, nucellus, micropyle, chalaza.
– Zygote’s first division establishes embryo polarity.
– Suspensor absorbs nutrients for embryo growth.
– Embryo components: cotyledons, epicotyl, plumule, hypocotyl, radicle.
– Monocotyledons have additional sheath structures for protection.
**Seed Coat Formation and Characteristics**:
– Seed coat forms from ovule integuments.
– Monocot and dicot seed coats may have patterns or textures.
– Seed coat derives from tissue of the mother plant.
– Grasses have seed coats fused with the fruit wall.
– Seed coat may have wings, tufts of hair, or textured markings.
**Seed Shape and Appearance**:
– Seeds exhibit diverse shapes and characteristics.
– Various terms are employed to describe the shape of seeds.
– Shapes range from bean-shaped (reniform) to globose.
– Surface textures vary from polished to roughened.
– Common colors, textures, and forms of seeds are described.
In botany, a seed is a plant embryo and food reserve enclosed in a protective outer covering called a seed coat (testa). More generally, the term "seed" means anything that can be sown, which may include seed and husk or tuber. Seeds are the product of the ripened ovule, after the embryo sac is fertilized by sperm from pollen, forming a zygote. The embryo within a seed develops from the zygote and grows within the mother plant to a certain size before growth is halted.
The formation of the seed is the defining part of the process of reproduction in seed plants (spermatophytes). Other plants such as ferns, mosses and liverworts, do not have seeds and use water-dependent means to propagate themselves. Seed plants now dominate biological niches on land, from forests to grasslands both in hot and cold climates.
In the flowering plants, the ovary ripens into a fruit which contains the seed and serves to disseminate it. Many structures commonly referred to as "seeds" are actually dry fruits. Sunflower seeds are sometimes sold commercially while still enclosed within the hard wall of the fruit, which must be split open to reach the seed. Different groups of plants have other modifications, the so-called stone fruits (such as the peach) have a hardened fruit layer (the endocarp) fused to and surrounding the actual seed. Nuts are the one-seeded, hard-shelled fruit of some plants with an indehiscent seed, such as an acorn or hazelnut.