Flowers - II

Carpel is composed of the stigma, style, and ovary and within the ovary are one to many ovules

Ovules

Ovule begins developing as a bulge in ovary wall and soon

a Megaspore Mother Cell (Megasporocyte) differentiates

The usual pattern of development

Female Gametophyte

Whole Ovule View

Ovule is an integumented megasporangium.

The wall of the megasporangium in known as the nucellus (nu)

Megaspore mother cell (MMC) prior to meiosis and after Division I

Nucellus

MMC undergoes meiosis to produce 4 megaspores – in the majority of angiosperms, 3 degenerate

Surviving megaspore undergoes 3 mitotic divisions producing 8 haploid nuclei (cells)

Mature Ovule (Female Gametophyte)

81% of angiosperms

***

Occurs in Lilium

Other patterns

Pollen production occurs in the anthers

Microsporangia

Cross section of unopened flower with 5 stamens

Young anther

Microspore mother cells differentiate in the microsporangia and undergo meiosis

Tapetum

Microspores develops into male gametophytes

Tetrads

Pollen grains are the male gametophytes

• Microspore nucleus divides producing two nuclei (cells)

• Microspore wall becomes the pollen wall

• Pollen released at two cell stage in the majority of angiosperms

Gametophyte development

Pollen TEM

Pollen wall is an elaborate multilayered wall with sporopollenin as the “unique” component

Pollen is described by aperature type

Pores

Culpi (furrows)

Exine surface

More exine patterns

Orientation of the grain

Alnus (alder) pollen Juniperus (cedar) pollen

Morus (mulberry) pollen Quercus (oak) pollen

Light and SEM views of ragweed and grass pollen