A method for the observation of cell division using acetic dahlia solution was introduced to lower secondary school science classes. Onion seeds with about 10 mm of the germinated portion could be stored in a refrigerator for at least one week in good condition for observing cell division. A staining temperature at 35°C resulted in a ten minute reduction compared to that of room temperature. These findings are useful for preparing specimens and observing dividing cells under a microscope in a limited time of lesson (50 min) in lower secondary schools.

Germinated seedlings of Allium cepa are suitable material for observing mitosis because they are easy to grow in a short time, and for finding mitotic cells with a simple staining method. The mitotic index which indicate the frequency of mitotic cells in the root meristem with 5-10 mm of root lengh at 23°C usually was higher than that with other root length. Under this temperature, the roots of most seedlings reached to 5 - 10 mm long within 3 or 4 days. When the class schedule changes, it is necessary to adjust the condition of seedling containing many mitotic cells. The way of maintaining the condition of the seedling was through refrigeration and then removal from the refrigerator after some days for observation of mitosis. These experiences suggested the followings: The mitotic index depends on the root length and not the temperature, therefore there is no difference between low temperature (2 - 3°C) and room temperature (23°C). Under low temperature the seedlings grew slowly and the majority became 5 - 10mm for three weeks after sown. Their mitotic index was similar to the seedling grown 5 - 25 mm in room temperature, therefore we can make seedlings from the higher frequency of mitotic cells when we change the schedule of school experiments. The seed stored with silica gel in a paper envelope and enclosed in a plastic bag for five years in a refrigerator and the mitotic index was examined when their seedling is 1 - 25 mm.