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Mayo (1989) has shown that the course of individual stylar canals is correlated with the type of placentation. Those species with basal or sub-basal ovules, such as P. tripartitum and P. smithii, have stylar canals which course down the center of the axis of the pistil and arise from near the base of the locules. Those species with axile placentation have stylar canals which also course down the pistil axis and enter the locule somewhere above the base of the locule, but only rarely at the very apex of the locule. The stylar canals are lined with papillose epithelial cells which are contiguous with the stigmatic epidermis (Mayo, loc.cit.). These secrete the gelatinous mucous which keeps the stigmatic surface moist.