Cotyledons are the nutrition source of the baby plant and they are present under the seed cover in most cases...cotyledons are of 2 types;monocotes and dicots.The embryo of the baby plant is present in between the 2 cotyledons in Dicots. E.g. soak a bean in water untill the seed cover breaks...then remove the seed cover and u will see 2 white structures...they are the cotyledons.
What i learnt was that cotyledons are of 2 kinds- 
Monocotyledons and Dicotyledons. We can i dentify them by the appearance of the leaf and the seeds present in the fruit of the plant.
1 1 1