central vacuole is formed. As the microspore nears the first pollen mitosis, the nucleus is pressed
up near the periphery of the microspore (Figure 17.1A). Staining will still be fairly light. Pollen
mitosis is of short duration, but it may sometimes be observed; it is recognized by the presence of
condensed chromosomes (Figure 17.1B). The product of the first pollen mitosis is a binucleate
microspore containing a large vegetative and a small generative nucleus. The vegetative nucleus is
often difficult to recognize because it is so diffuse and lightly staining. However, this stage may
be definitively identified by the presence of the small densely staining generative nucleus (Figure
17.1C). As the binucleate microspore ages, the intensity of the staining increases and starch granules
begin to accumulate (Figure 17.1D). Eventually, both nuclei may be hidden by the dark staining
starch granules.