Double Fertilization

1. Pollination occurs – transfer of pollen from anther to stigma2. Pollen tube forms in the stigma and produces two sperm3. The sperm enters into the ovule through the micropyle4. One sperm nucleus (n) unites with the egg nucleus (n) to become the zygote (2n)5. The other sperm nucleus (n) unites with the two polar nuclei to form a triploid (3n) endosperm nucleus – provides food for the developing embryo.

In many plants the endosperm disappears and the cotyledon becomes the food source

Hilum – scar on a seed coat marking where it was attached to the ovaryMicropyle – small opening within the hilum. Pollen tube enters here

Coleoptile - the covering of the young shoot of the embryo Hypocotyl - the embryonic axis below the point of attachment of the cotyledon and above the radicle. It becomes the stemCotyledon (kot-uh-le-don) – seed leaf in plant embryo Radicle - embryonic root of a plant Epicotyl - embryonic axis above the point of attachment of the cotyledon. It becomes the leavesMonocot – a plant that produces seeds having one cotyledon, such as cornDicot – a plant that produces seeds having two cotyledons

Placenta – part of the ovary wall where the ovules develop at the fused margins Funiculus – attaches the plant ovule to the placenta in an ovary

Cross-Section of a Cucumber Fruit