Wound-induced callus formation has long been observed and
used in various contexts from debarking of trees (Stobbe et al.,
2002) to horticultural use of propagation (Cline and Neely, 1983).
These calli often accumulate phytoalexins and pathogen-related
proteins (Bostock and Stermer, 1989) and thus are thought to
prevent infection as well as water loss. Wound-induced callus
derive from various cell types, including vascular cells, cortical
cells, and pith cells. In some cases, wound-induced calli regenerate
new organs or new tissues, suggesting that they are
highly pluripotent (Stobbe et al., 2002).