Mitosis in Onion Root Tips.

Onion root tips are extremely popular for viewing the different phases of mitosis because the chromosomes are large and and very dark when stained. The images shown below were taken using a regular light microscope with an oil immersion lens at 1000X. Note that the actual magnification of the image will depend on the size of your monitor. The real size of a typical onion root tip cell is about .075mm (75 micrometers).


The two cells at the left are in interphase. The material inside the nucleus is largely chromatin(C) which consists of the chromosomes stretched out so that individual chromosomes are not visible. The dark structure(I) represents the nucleolus. Interphase cells typically have one or more nucleoli.


Observe the condensing chromosomes (dark regions) in the cell on the left below in early prophase. Note the cell on the right below with more prominent chromosomes and having lost the nuclear envelope.

stage H                stage G


This a very nice metaphase cell. Observe the chromosomes(Ch) at the equator of the spindle. The spindle(S) is highly visible. especially on the lower half of the cell.





The cell to the left is a nice mid anaphase. If you closely compare the chromosomes with the metaphase cell, you can tell that the chromosomes are now unduplicated.





Telophase and Cytokinesis

The arrow is pointing to the spindle of this telophase cell. Also, there is a faint cell plate that may not show up on all monitors. In plant cells cytokinesis involves the formation of a cell plate. This is the start of the cell wall that will eventually divide the two new cells.



Late Telophase.

This image shows a late telophase cell near the left hand side of the image. Note that the cell plate goes almost all the way across the original cell and the reforming of the nuclear envelope.





Practice locating each of the stages of mitosis in the following slides of the onion root tip. Each picture contains at least one cell at each stage of mitosis (and some stages are represented by multiple cells). Onion root tip slide 1
Click here for a key that identifies the phase of the cell cycle in these two photomicrographs
Onion root tip slide 3


Acknowledgement: this page is adapted from a similar pages available at and