Part 4 - Angiosperm seed plants - Flowering plants

Photos by Lee Sola, Glendale Community College, Glendale, Arizona
(These photos are protected by copright and may not be reproduced without written permission.)

This is a photo of a flower (a lily), the reproductive structure of an angiosperm (flowering plant). A is the tip of the carpel (female part of the flower). B is one of several stamens (male parts of the flower).  Usually, stamens surround the pistil. Pollen grains develop inside the capsule (anther) at the tip of a stamen.  A pollen grain is a protective container for sperm. Pollen grains land on the tip of the pistil.  A tube grows from each pollen grain down to the ovary and deposits sperm next to an ovule.

This photo shows the same flower cut open. C is the tip of the carpel (female part, same as A in the photo above). A and B are the stamen (male part, same as B in photo above). E is the swollen lower part of the pistil, the ovary. The ovary (E) contains ovules (not shown in photo).  Each ovule inside the ovary contains an egg cell. If fertilization occurs, the fertilized egg grows into a small plant embryo. The ovule containing the embryo hardens, becoming a seed.  The ovary with seeds inside is now called a fruit. Seeds are released from an ovary in various ways (they may split open, or be eaten by an animal who discards or defecates the seeds, etc.). If a seed lands in a favorable spot, the embryo inside it may grow, emerge from the seed (germination), and develop into a new flowering plant.

This drawing shows a mature ovule (seed) from a bean plant, opened (one cotyledon removed) to reveal the embryo that will grow into a new plant. First, the root tip will grow, establishing contact with the soil (and probably symbiotic fungi) for water and mineral uptake. Then the stem/root axis will elongate, bringing the young leaves into the light.  Initially, growth of the embryo will use the food stored in the cotyledons. When exposed to light, the young leaves and stem will turn green as their chloroplasts mature.  Now the young plant can make its own food and continue to grow, eventually producing flowers and seeds of its own..