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Fig. 9.3-9. Transverse section of stamen in lemon flower (Citrus limon). This is a transverse section of the anther, the part of the stamen that actually produces the pollen grains. As part of pollen development, the cells lining the anther lumen – a layer known as the endothecium – secretes materials that are essential for the proper maturation of the pollen grains. In many cases, secretory processes in plants involve interaction with animals (deterring herbivores or attracting pollinators), but in processes like this in the anther, the secretion is a mechanism by which one part of a plant affects another part of the same plant.

            The cells of the endothecium are so densely cytoplasmic that no vacuoles at all are visible; it is even difficult to distinguish one cell from another in most of the endothecium. The dark red dots in the both the endothecium and the pollen grains are nucleoli, with the actual nuclei being just barely visible around a few of them (all nucleoli occur only in nuclei – where we cannot see the nuclei, it is due to weak staining).