Origin of callus

Callus arises from proliferating cells of the parent tissue. In culture,
callus is initiated by placing small pieces of the whole plant (explants)
onto a growth-supporting medium under sterile conditions. Hormones
change the metabolism of the cell from quiescent to metabolically active.

Callus arising
from leaf tissue

Callus arising from
vascular tissue

Callus arising fro
m root tissue

Callus arising from
embryo tissue

Photo indicating where
the callus (c) arises from