Actually the term angiosperms means naked seeds,it is a greek word. and in testa and tegmen,which are to layers helps in develop of seed. cotyledons are food  storage structures which nurish the seed ,thats why they are considered as imp part of seed.
The word angiosperms means seed. the seeds develop inside an organ which is modified to become a fruit. these are also called flowering plants. plant embryos in seeds have structures called cotyledons. cotyledons are called 'seed leaves' because in many instances they emerge and become green when the seed germinates. thus, cotyledons represent a bit of pre-designed plant in the seed. the angiosperms are divided into 2 groups on the basis of the number of cotyledons present in the seed. plants with seeds having a single cotyledon are called monocotyledonous or monocots. plants with seeds having two cotyledons are called divots.
the last line divot will be dicot.
sorry mistake hapeend. forgive me.