Callus »Definition, Features, and More with Illustration

Callus - botanical definition with explanations

Bulge-like growth of new tissue from undifferentiated cells on the edges of cuts and other injuries on woody vegetation. In the further course of the process, extensive overburdening of the wound from the outside inwards.

Characteristic for callus is that the tissue is formed directly from the thin cambium ring, which is located below the bark and bast, as shown in the figure below.

Callus thus contributes to wound healing - the process in detail

On woody plants, every injury offsets the exposed Cambium on alert. Fungal spores and pests lurk on every open wound on bushes and trees as an ideal target. Only rapid wound healing reduces the latent risk of infection. In order for the healing to take place on its own, the cambium tissue goes through a process of transformation and becomes callus, which quickly overflows the wound. The following overview explains the individual phases of this exciting process:

• First phase: Callus formation in the form of irregularly shaped tissue cells as a small bulge along the wound edges
• Second phase: soft tissue forms bark tissue on the outside, wood tissue on the inside
• Third phase: fresh tissue covers the wound on all sides

Smaller cuts are covered with callus tissue within a short time. In the case of larger wounds, however, the process can drag on for many years. As soon as the wound edges meet in the center, the damaged tissue underneath is cut off from the air supply. Any fungi and pests that have already settled will die off.

The inwardly directed tissue cells close exposed vessels and form tannins. If rot and mold have already spread, these problem areas are separated from the rest of the tree by the tannin barrier.

Wound closure torpedoes callus function

We owe our knowledge of how callus works to the father of modern tree care, Alex Shigo. This goes hand in hand with the logical conclusion that any wound closure counteracts the self-healing process of woody plants. Since then, the use of impermeable sealants for treating wounds after a tree cut has been frowned upon - with one exception:

If a wound is caused on the tree or bush in the middle of winter, the exposed cambium should be protected from frost damage. To do this, smooth out the injury with a knife. Then coat the edges of the wound with a thin layer Tree wax,(€ 18.62 at Amazon *) to cover the valuable dividing tissue under the bark until next spring. This procedure is recommended for cuts with a diameter of 2 centimeters or more.