How many cells are in mitosis in an onion root tip?

Based on the provided reference, in a sample of 100 onion root tip cells, 42 cells are in one of the phases of mitosis.

Here's a breakdown:

• The reference states that "42 cells of the 100 cells are in one of the phases of mitosis."
• This indicates the number of cells undergoing mitosis in that specific sample.

Therefore, in this particular observation, 42% of the cells were actively dividing. This percentage is known as the mitotic index.