Answer:
The correct answer is: The process of cytogenesis.
Step-by-step explanation:
Schwann is well-known as the Father of Cell Theory as his investigations on plants via microscope along with the observations of Schleiden about notochord, they discovered that all living things are made of CELLS, and that all kinds of parts of living things have their origins in cells. These discoveries were the base of the Cell Theory and they encouraged the scientific concern about the embryos, which founded embryology.
Now, they also believed that all cells had nucleus and therefore this was a fundamental element in cytogenesis (generation of cells), for new cells had their origin in a crystallization process in a jelly material that formed nuclei.
But this was proven wrong for Modern Cell Theory stands that some cells don't have nucleus, and that cells are generated by other pre-existing cells through division or fusion process and not by a jelly material in which the nucleus is crystallized.