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).
To return from a diploid stage to a haploid stage, meiosis must occur. In regard to changes of ploidy, there are 3 types of cycles: haplontic life cycle â the haploid stage is multicellular and the diploid stage is a single cell, meiosis is zygotic.