BIO 1510: Lecture Exam 3-3: 36

After fertilization, the plant embryo grows & develops

Once meristems and cotyledons (seed leaves) differentiate, development stops (or, the embryo becomes dormant)

Outer layers of the ovule develop into a relatively impermeable seed coat, enclosing the dormant embryo and endosperm (stored food)

Mature seeds contain between 5% - 20% water

Postpone development until favorable conditions are present

Afford maximum protection to the young plant at its most vulnerable stage of development

Contain stored food permitting development before photosynthesis starts (Endosperm)

Have specific dispersal mechanisms, facilitating migration of alleles into new gene pools

seed leaves

stamen
sperm are made in anther

pistel which contains ovary

Fruits are mature ovaries

follicles, legumes, samaras, nuts, grains

drupes, berries, hesperidia, pomes, pepos

develop from many ovaries of a single flower

strawberries, blackberries

develop from a cluster of flowers

pineapple, mullberry

Birds – fruits with fleshy coverings, usually shiny black, blue, or red

Mammals
- fruits with hooked spines that attach to fur
- fruits buried by squirrels or other mammals (nuts)

Wind – maples, elms, dandelions, cottonwoods, etc.

Water – beach plants (like coconuts)

The resumption of growth and development by a spore or seed

Only occurs when water is absorbed, which breaks the seed coat

Sufficient oxygen must be present for development to continue

Thus very few types of seeds can germinate under water

Cellular respiration resumes, using oxygen & food stored in seed

Roots emerge first, then cotyledons

connects root system to cotyledons