Overstaining of the cells

You are observing the onion root tip at 40x and you can see the nuclei but not the chromosomes so 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 because the slide  is overstained everything looks line a big blob.

Martha has a look and appears confused.

Martha: I can see the cells clearly. I don’t think that there is a problem with the staining of the slide. Something else is going on but I’m not sure.

You: That was helpful, thanks Martha. Let me have another look.

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