How do angiosperms differ from gymnosperms?
First, the seeds of the angiosperms, a more recently evolved and highly successful division of the
tracheophytes, are enclosed within a protective chamber, the ouary. A ripened ovary containing seeds is
called a fruit. The fruit not only encloses the seeds but may also aid in seed dispersal. The fruit is either
carried or eaten by animals that migrate to distant sites, carrying the seeds with them; the seeds are
ultimately dropped or eliminated from the animals’ digestive tracts.
The seed also forms a little differently in angiosperms. One sperm nucleus from the pollen tube unites
with an egg nucleus to produce the zygote. A second sperm nucleus unites with two haploid nuclei in the
gametophyte (embryo sac) to produce the triploid endosperm, an important source of food within the seed
for such seeds as corn.
In gymnosperms, pollination (transfer of pollen to female reproductive structure) can be only windborne.
In flowering plants, pollen may be transferred by wind or by animals. Although insects have been
stressed as prime agents for pollination, recent studies suggest that mice and other small mammals may
also play a role, particularly in tropical plants.
A major internal modification of the angiosperms is the development of specialized xylem cells, the
uessels and fibers, in addition to tracheids. The vessels are particularly significant because they are large-bore
columnar cells that anastomose (join) end to end. When their inner cellular contents degenerate, they
collectively form long tubes that greatly facilitate the passage of water in the plant. Fibers, on the other
hand, function solely to provide support. In conifers the single xylem elements, the tracheids, represent a
more primitive condition.
First, the seeds of the angiosperms, a more recently evolved and highly successful division of the
tracheophytes, are enclosed within a protective chamber, the ouary. A ripened ovary containing seeds is
called a fruit. The fruit not only encloses the seeds but may also aid in seed dispersal. The fruit is either
carried or eaten by animals that migrate to distant sites, carrying the seeds with them; the seeds are
ultimately dropped or eliminated from the animals’ digestive tracts.
The seed also forms a little differently in angiosperms. One sperm nucleus from the pollen tube unites
with an egg nucleus to produce the zygote. A second sperm nucleus unites with two haploid nuclei in the
gametophyte (embryo sac) to produce the triploid endosperm, an important source of food within the seed
for such seeds as corn.
In gymnosperms, pollination (transfer of pollen to female reproductive structure) can be only windborne.
In flowering plants, pollen may be transferred by wind or by animals. Although insects have been
stressed as prime agents for pollination, recent studies suggest that mice and other small mammals may
also play a role, particularly in tropical plants.
A major internal modification of the angiosperms is the development of specialized xylem cells, the
uessels and fibers, in addition to tracheids. The vessels are particularly significant because they are large-bore
columnar cells that anastomose (join) end to end. When their inner cellular contents degenerate, they
collectively form long tubes that greatly facilitate the passage of water in the plant. Fibers, on the other
hand, function solely to provide support. In conifers the single xylem elements, the tracheids, represent a
more primitive condition.
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