Seed

**Evolution and Diversity of Seed Plants:**
– Land plants evolved around 468 million years ago
– Gymnosperms appeared during the late Devonian period
– Seed ferns evolved during the Carboniferous period
– Seed plants dominate biological niches on land
– Different groups of plants have modifications for seed protection

**Seed Development and Components:**
– Angiosperm seeds are enclosed in a fruit for protection
– Gymnosperm seeds develop naked on cone bracts
– Angiosperm seeds consist of embryo, endosperm, and seed coat
– Seed development starts with double fertilization in angiosperms
– Endosperm tissue provides food for the young plant after germination

**Ovule Structure and Development:**
– Ovule components include funicle, nucellus, micropyle, and chalaza
– Ovule shape affects the final seed shape
– Zygote’s first division establishes embryo polarity
– Suspensor absorbs nutrients for embryo growth
– Ovule shapes include anatropous, orthotropous, campylotropous, and amphitropous

**Embryo Formation and Structure:**
– Embryo components are cotyledons, epicotyl, plumule, hypocotyl, and radicle
– Cotyledons are seed leaves providing nutrients
– Plumule becomes the shoot upon germination
– Hypocotyl is the stem-root transition zone
– Monocotyledonous plants have additional sheath structures

**Seed Coat Composition and Characteristics:**
– Seed coat forms from integuments of the ovule
– Seed coat consists of tegmen and testa layers
– Seed coats may have patterns, textures, wings, or hair
– Monocot and dicot seed coats may be distinct or fused with pericarp
– Funiculus detaches after seed coat formation