Seed Plants Seed = embryo sporophyte, encased in and dispersed with gametophytic and maternal sporophytic tissues. Gymnosperms – seeds “naked” in cones Angiosperms – the flowering plants seeds enclosed in carpels carpel = modified leaf fused around seeds; becomes fruit

Gymnosperms – 4 Phyla Cycadophyta – the cycads. Superficial resemblance to palms, but have cones true palms have flowers & fruits like dates or coconuts Ginkgophyta –1 living species, Ginkgo biloba Gnetophyta – Strange group; classification unsure Coniferophyta – the conifers: pine, spruce, fir, cedar, redwood, cypress, etc.

Highly reduced gametophytes Male gametophyte is the pollen grain. In gymnosperms, it consists of about 4 cells. One of these is the sperm nucleus. Whole gametophyte is dispersed by wind. No motile cells.

Ovule Immature seed Female gametophyte consisting of about 1000 cells (in gymnosperms). Surrounded by Integuments - layers of maternal sporophytic tissue. Opening in the integuments, called the micropyle, allows sperm access to eggs.

Figure 29.5 The Life Cycle of a Pine Tree Seed cone Scale of seed cone Section through scale Functional megaspore HAPLOID (n) Gametophyte generation Meiosis Ovule Megasporangium Female gametopyte Pollen cones Micropyle Female gametopyte Reduced archegonium Microspore mother cells Egg Microspores Section through scale Sporophyte Scale of pollen cone Pollen grain (1 of 4) Male gametophyte (germinating pollen grain) Fertilization Seed coat Female gametophyte Zygotes Embryo Female gametophyte Seed cone Seed Winged seed DIPLOID (2n) Sporophyte generation Wing Developing embryo Scale of seed cone

Figure 29.5 The Life Cycle of a Pine Tree

The Flowering Plants The phylum Angiospermae (also known as Anthophyta or Magnoliophyta) Most numerous living plant group (250,000 spp.) (only ~750 species of gymnosperms, 12,000 ferns) Characteristic features: Ovules and pollen produced in flowers. Ovules contained inside carpels. Double fertilization forming triploid endosperm.

Carpel (Pistil) Stamen

Ovules within carpels Seeds within fruits.

Angiosperm gametophytes Highly reduced. Male gametophyte is pollen grain with 3 haploid nuclei. Female gametophyte is 8 nuclei inside the ovule. One of the 8 is the egg cell. Two are “polar nuclei” and are important in double fertilization.

Figure 29.10 The Life Cycle of an Angiosperm Stigma DIPLOID (n) Carpel Style Anther Ovary Stamen Filament Ovule Megaspore mother cell Microspore mother cell Endosperm nucleus (3n) Meiosis Meiosis Surviving megaspore Zygote (2n) Pollen grain (male gametophyte) Double Fertilization Female gametophyte with 8 haploid nuclei Tube cell nucleus Sperm Pollen tube HAPLOID (n)

Double Fertilization One sperm nucleus fertilizes the egg, forming a zygote, which grows into an embryo (as you would expect). Another sperm nucleus fuses with the two polar nuclei, forming a triploid cell. This divides by mitosis to form a triploid tissue called endosperm. Endosperm acts as a nutritive tissue for the developing embryo. For more detail, see pp. 666-669.

Angiosperm groups Primitive angiosperms: Monocots: Eudicots: No vessels in wood; No fusion of carpels. Monocots: One embryo leaf; parallel veins in leaves; flower parts in multiples of 3 Eudicots: Two embryo leaves; netted veins in leaves; flower parts in multiples of 4 or 5.