text: what is the purpose of adding an onion root tip into the  carnoy fixative in the onion mitosis experiment? besides that, why is the onion root tip is added to the hydrochloric acid before transfering it into the carnoy fluid? the fixative instantaneously stops mitosis so when you eventually see the chromosomes, you are looking at one moment of mitosis frozen in time.  the hcl will chemically break down the middle lamellae which will allows the meristematic cells to spread easily.