The aura can be in the form of prismatic colors, flashes of light, and sometimes stars. They usually last about 20 minutes and then go away. If these flashes or lines of light occur without a headache, it is called an ophthalmic migraine, or a migraine without a headache.
In gymnosperms and flowering plants, the megaspore is produced inside the nucellus of the ovule. During megasporogenesis, a diploid precursor cell, the megasporocyte or megaspore mother cell, undergoes meiosis to produce initially four haploid cells (the megaspores).
Cells undergo mitosis to replace dead cells. If there is/are cell(s) absent in any part of the body, mitosis occurs to replace the missing cell(s). So basically, if an organism is able to keep all its cells from being harmed in any way, mitosis will never be required as no cell will need replacement. Meiosis: Cells undergo meiosis to form gametes (sex cells).