While double fertilization is a later topic, the structure 'Central Cell' is prepared for it. Before fertilization, the
In the mature embryo sac prior to fertilization, the central cell contains two polar nuclei. While they may fuse just before fertilization to form a secondary nucleus (2n), the typical description of the mature sac characterizes the cell as having two polar nuclei (n+n).
Ref: Central part of the embryo sac showing two distinct polar nuclei.