In which plants' life cycle does double fertilization occur?

Explanation:

The process of double fertilization occurs in the life cycle of angiosperms. Angiosperms are the flowering plants which exhibit stems, roots and leaves. The seeds of the angiosperms remain enclosed in the flower. The double fertilization takes place when one pollen nuclei  fuses with the egg to form a zygote and the other fuses with the  polar nuclei (two) so as to form endosperm.  

a "theory" a suggestion that is not 100 % accurate, or a figure. some people say its a theory because they of all the passed theory's about one subject. it depends sometimes theory might be accurate and sometimes they are.