Summary
For fertilization to occur in angiosperms, pollen has to be transferred to the stigma of a flower: a process known as pollination. Gymnosperm pollination involves the transfer of pollen from a male cone to a female cone. When the pollen of the flower is transferred to the stigma of the same flower, it is called self-pollination.
Cross-pollination occurs when pollen is transferred from one flower to another flower on the same plant, or another plant. Cross-pollination requires pollinating agents such as water, wind, or animals, and increases genetic diversity. After the pollen lands on the stigma, the tube cell gives rise to the pollen tube, through which the generative nucleus migrates. The pollen tube gains entry through the micropyle on the ovule sac.
The generative cell divides to form two sperm cells: one fuses with the egg to form the diploid zygote, and the other fuses with the polar nuclei to form the endosperm, which is triploid in nature. This is known as double fertilization. After fertilization, the zygote divides to form the embryo and the fertilized ovule forms the seed. The walls of the ovary form the fruit in which the seeds develop. The seed, when mature, will germinate under favorable conditions and give rise to the diploid sporophyte.
Glossary
accessory fruit
fruit derived from tissues other than the ovary
aggregate fruit
fruit that develops from multiple carpels in the same flower
aleurone
single layer of cells just inside the seed coat that secretes enzymes upon germination
coleoptile
covering of the shoot tip, found in germinating monocot seeds
coleorhiza
covering of the root tip, found in germinating monocot seeds
cotyledon
fleshy part of seed that provides nutrition to the seed
cross-pollination
transfer of pollen from the anther of one flower to the stigma of a different flower
dormancy
period of no growth and very slow metabolic processes
double fertilization
two fertilization events in angiosperms; one sperm fuses with the egg, forming the zygote, whereas the other sperm fuses with the polar nuclei, forming endosperm
endocarp
innermost part of fruit
endosperm
triploid structure resulting from fusion of a sperm with polar nuclei, which serves as a nutritive tissue for embryo
endospermic dicot
dicot that stores food reserves in the endosperm
exocarp
outermost covering of a fruit
epicotyl
embryonic shoot above the cotyledons
gravitropism
response of a plant growth in the same direction as gravity
hypocotyl
embryonic axis above the cotyledons
mesocarp
middle part of a fruit
multiple fruit
fruit that develops from multiple flowers on an inflorescence
nectar guide
pigment pattern on a flower that guides an insect to the nectaries
non-endospermic dicot
dicot that stores food reserves in the developing cotyledon
pericarp
collective term describing the exocarp, mesocarp, and endocarp; the structure that encloses the seed and is a part of the fruit
plumule
shoot that develops from the germinating seed
pollination
transfer of pollen to the stigma
radicle
original root that develops from the germinating seed
scarification
mechanical or chemical processes to soften the seed coat
scutellum
type of cotyledon found in monocots, as in grass seeds
self-pollination
transfer of pollen from the anther to the stigma of same flower
simple fruit
fruit that develops from a single carpel or fused carpels
suspensor
part of the growing embryo that makes connection with the maternal tissues
tegmen
inner layer of the seed coat
testa
outer layer of the seed coat
vernalization
exposure to cold required by some seeds before they can germinate