A higher magnification is needed to observe the cells

You are observing the onion root tip at 40x and you can see the nuclei clearly. You ask your lab partner to have a look.

You: Martha can you please have a look at this. I think I can see the nuclei but I cannot make out the different phases of mitosis. Do you think that we need to move to 100X magnification?

Martha has a look and appears confused.

Martha: I can see well-defined nuclei in all cells so I think the magnification is appropriate. This is a different problem.

You: Ok I will have another look.

What is the most likely reason you are unable to identify the stages of mitosis in the onion root tip slide?