The cambium has been variously defined as follows: "The actively
dividing layer of cells that lies between, and gives rise to, secondary
xylem and phloem (vascular cambium)" (IAWA 1964); "A meristem with
products of periclinal divisions commonly contributed in two directions
and arranged in radial files. Term pre- ferably applied only to the two
lateral meristems, the vascular cambium and cork cambium, or phellogen"
(Esau 1977); and, "Lateral meristem in vascular plants which produces
secondary xylem, secondary phloem, and parenchyma, usually in radial
rows; it consists of one layer of initials and their undifferentiated
deriva- tives" (Little and Jones 1980). Clearly, the cambium is a
diverse and extensive meristem, and no one defini- tion will encompass
all manifestations of what anatomists consider cambium. Its diversity
and extent are further exemplified by a single plant, such as a
temperate- zone tree, in which procambium is initiated in the embryo and
perpetuated throughout every lateral, primary meristem before giving
rise to cambium in the secondary body. The cambium thereafter performs
its meristematic task of producing daughter cells that differentiate to
specialized tissue systems. The cam- bium, however, does not remain
static. Its derivatives vary either in form, or TImc- tion, or rate of
production at different positions on the tree, with age of the tree, and
with season of the year. Moreover, the cambium responds both to internal
sig- nals and to external stimuli such as environment or wounding.