The development of the carposporophyte in Kallymenia reniformis involves an elaborate series of interactions between reproductive and vegetative tissues. Following fertilization, the inner cells of the carpogonial branches form processes that unite with the supporting cell and with each other, giving rise to a large fusion cell. A number of medullary filaments are enveloped and incorporated within the developing fusion cell. Secondary filaments may be produced from medullary cells outside the fusion cell after connecting filaments have been initiated. Connecting filaments are nonseptale and wind their way through the medulla. The presence of a connecting filament in the vicinity of an auxiliary cell appears to initiate a complex sequence of responses. Vegetative filaments are produced in the medulla and inner cortex that grow centripetally toward the auxiliary cell and fuse with one another, forming a network of secondary tissue. One of the vegetative cells may penetrate the auxiliary cell, while others intrude into subsidiary cells connecting them with the network. An ostiolate pericarp is initiated in the cortex above the auxiliary cell. The connecting filament fuses with the auxiliary cell and also with some of the surrounding vegetative cells, forming an irregular lobed structure. Gonimoblast is initiated in scattered pockets from vegetative cells in the vicinity of the auxiliary cell apparatus.