During what stage of embryonic development in plants do the cotyledons begin to appear and rapid cell division takes place?

Answer: The Heart stage.

Explanation:

Embryonic development or embroyogenesis refers to all the process that take place after the fertilization of ovule to give rise to develped plants embryo. This occur during single or double fertilization.

There are six stages of embryonic developments and they are; the two cells stage, eight cells stage, globular stage, Heart stage, torpedo stage and maturation stage.

The Heart stage is the transition stage where cotyledons that to develop and elongate, rapid cell division occur.