As was true in the gymnosperms, the "main
plants" in angiosperms are sporophytes, while the gametophytes
are confined to the flowers, usually male and female together. Male gametophytes are called
female gametophytes are pistils. The pollen
from the stamen has to reach the pistil and make a pollen tube
to the base of the flower, the ovary, and the ovules,
where the egg cells are. Once the egg cells are fertilized,
the embryos are sealed up with food in a seed and the ovary is
converted into a fruit.
The seeds often wait for some environmental cue, such as warmth,
moisture, or light periods shifts, before
sprouting. A type of growth hormone known as
which settled to the bottom of the sprouting root and stem as they
emerge, have different effects on those parts: auxin-soaked
root cells grow more slowly, making the top of the root grow faster
and curve the root downward; auxin-soaked stem cells grow
faster, curving the stem up.
mature plant, auxins migrate away from the sunlit side of the plant
- if the light is coming in from the side, the migration causes the
stem to curve toward the light as it grows and better orient the
leaves to catch light. Plants
produce many different
types of hormones that can affect reproduction, overall
growth, defenses, fruit ripening, and other features.
of new cells in plants happens in a type of tissue called the meristem.
Meristems can be, and usually are, at the growing tips of the
plants, where they are called
Most plants add new cells from the tips out, not evenly all over and not from
the bottom up - in the other parts of the plant, the cells
grow but do not divide. Leaves, branching stems or
roots, and flowers
all are produced by apical meristems.
Some growth may also occur along the sides of the
plants, such as is found in the
rings of trees - these are called
meristems. These make
tree ring patterns in ecosystems with
growing seasons, where growth produces big,
"light" cells, alternating with seasons of less growth
(cold winters or dry periods), which produce smaller,
"darker" cells - each light/dark zone is a ring, and the
wider, lighter the ring, the better the growth season, leaving a
record of year-to-year climate.