Development of more than one embryo in a seed is called polyembryony. It can be cleavage polyembryony or adventive polyembryony depending upon how is it caused.
Polyembryony:
Normally in plants, one seed contains only one embryo but sometimes more than one embryo develops in a single seed. Development of more than one embryo from ovule, seed or fertilized ovum is called polyembryony. Polyembryony is found in both plants and animals.
In 1719, Antony Von Leeuwenhoek first described polyembryony in Citrus fruit (Orange). It is a common feature in gymnosperms whereas it is found only in few genera of angiosperms such as lemon, blackberry, tobacco, Allium, Crotalaria etc. In most cases of polyembryony, one embryo only matures in one seed and other embryos are destroyed during embryo development.
Some plants such as Vanda, which is an epiphyte, many mature embryos are found at the time of seed germination.
Causes of Polyembryony in Angiosperm:
Polyembryony is a general feature of gymnosperm but it can occur in angiosperms due to following reasons:
1. Cleavage in proembryo.
2. Development of any other cell of embryo sac along with egg cell.
3. Development of more than one embryo sac is one ovule.
4. Overactivity of sporophytic cells of ovules.
