The development and patterning of stomata and glands in the epidermis of Peperomia

The leaf epidermis of Peperomia obtusifolia includes both stomata and glands, distributed in a joint spacing pattern. The questions asked concerned the relations between the development of glands and stomata and the determination of their distributions within the epidermis. For these purposes it was essential to follow development in vivo, by repeated replicas of the same epidermal surface. The development of both stomata and glands started by characteristic divisions. These were generally unequal and it was the smaller product that became the mother cell of the future specialized structure. The initial divisions differed, so that the nature of the mature structure, as a stoma or a gland, could normally be predicted at an early stage. But glands and stomata still shared developmental processes: their formation involved additional characteristic divisions in the mother cell and oriented divisions in neighbouring cells. Furthermore, some lineages started as glands and matured as stomata and vice versa. Statistical measurements showed that each individual structure was surrounded by a region that was free of both similar and other specialized structures. Where these regions involved stomata they could be accounted for by the cell lineages forming not only a stoma or a gland but also their surrounding cells. Yet the relations between neighbouring glands had an additional component, indicating a specific inhibition that declined gradually as the distance from the gland increased.