Figure 3. The Central American myrmecophytes of Piper section Macrostachys. (a) Longitudinal section through the stem and petiole of P. cenocladum. The chamber formed by the sheathing petiole forms the primary domatium in these species (white arrowhead). Note the excavated domatium in the stem cavity (white arrow) and the passage between petiolar and cauline domatia (black arrowhead). Pearl bodies are produced in the petiolar chamber (black arrows). The larger white structures are ant larvae and pupae, and two castes of workers are visible. Photo by Greg Dimijian. (b) Cross section of an unexcavated stem of P. sagittifolium from the youngest internode. (c) Cross section of an older, excavated portion of the same stem (third youngest internode). (d) Close up of the wall of the stem cavity showing the well-defined wound response layer. (e) Close up of the wound response later. Note the additional cell divisions and the differentiated cell walls in this section (indicated by the difference in color).