Answer:
This is because must of the cell must be in INTERPHASE.
Explanation:
The onion root tip is the growing part of the onion and many cells in it undergo mitosis. In the lab, it is prepared in a way that the cells become flat on the microscope slide so that you can observed them well.
In the cell cycle, most of the onions root tip cells are in interphase, they spend most of their life in interphase. In interphase, there is no observable changes in the celks, the cells keep on growing and the nucleus is been duplicated. This is because most of the onion root cells spend most of their time reproducing and growing in the interphase stage. During the interphase, the cells can still be seen in dark spots because the nucleus is still present and prophase has not started yet.