The origin of callus from the exposed surface of the cambial zone in Trema orientalis Bl. and Julbernardia globiflora (Benth.) Troupin is described and discussed in relation to what has been observed in other species. It is suggested that in different species callus may develop from any of the undifferentiated centripetal products of the vascular cambium, but that the kind of tissue contributing to callus initiation depends upon the species and on the histology of the cambial zone. The establishment of a new vascular cambium and phellogen is also described. It is found that cambium formation is not dependent on the presence of a preexisting cambium in the surrounding tissues and that the first-formed xylem is abnormal in structure.
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A.R.A. Noel (1968) studied this question.