• Making Your Slide: 
1. Choose a very long root and cut off about a 0.5 centimeter (1/4 inch) of the root tip.
2. Place the tip on a slide and add two drops of 0.5M hydochloric acid (HCl) to the tip.
   
3. Let the root tip soak in the HCl for 10 minutes. (The HCl helps break apart the tissue so the cells can be seen better.)
   
4. After 10 minutes, use a paper towel to carefully soak up all of the HCl. (Do not suck up the root tip.)
5. Place one or two drops of freshly filtered 1-2% aceto orcein stain on the tip, then suck it off and discard the stain.
6. Again, place one or two drops of freshly filtered 1-2% aceto orcein stain on the tip and stain for 20-30 minutes. DO NOT LET IT EVAPORATE
   
7. Remove the stain by sucking it off with a pipette. (Do not suck up the root tip.)
8. "Wash" the tip with water by adding a drop of water to the tip, then suck it off and add a fresh drop of water.
   
9. After 2-3 minutes, remove most of the water with a pipette (leave a small drop).
   
10. Place a coverslip over the root tip.
11. Using a ballpoint pen with the tip retracted, tap on the coverslip over the tip until it breaks up.
12. Place the slide with coverslip in place on paper toweling and fold the toweling over the slide.
13. Press straight down directly over the tip, but do no let it slide side to side.
14. Observe on low power (10X lens) then on high power if you find dividing cells.
15. If the cells are not sufficiently stained, add a drop of aceto orcein at the edge of the slide and let stain some more.
16. If the cells are clumped together, add a little stain to the edge and try tapping with a pen more vigorously.
17. To preserve the slide, carefully ring the coverslip with fingernail polish to prevent drying out.
    

Note: Wherever you see the (DNA molecule), there is a question that requires you to write an answer.

Find an interphase cell and cells representing all four stages of mitosis and sketch each below. (I will also photograph good examples.)

Allium has a diploid number of 16. How many chromatids are present at metaphase in these root-tip cells?_______  In the sperm nucleus in the pollen tube?_________

A cell in prophase has twice as many chromatids as a cell that has just finished telophase. Yet both are considered to be diploid cells. Why is this so? (Remember the definition of diploid.)

Turn this exercise in either today or at the first of next class session.