The histogenesis of callus in Coffea canephora stem explants and the discovery of early embryoid initiation

In stem explants of Coffea canephora all parenchymatic tissues between epidermis and vascular cambium were found to be capable of being transformed into callus tissue, the cortex being the most active layer in this respect. The initial callus cells enlarge and divide periclinally. As a result, the epidermis is ruptured so that the callus emerges. The possible rols of the parenchymatic tissues of the stele in the formation of callus occasionally observed on the cut surfaces of the explants has not been further investigated. After 14 days of incubation proembryo-like structures could already be observed in the zone of callus formation.