Cuttings. - When a cutting of Pelargonium, Willow, or other plant is made, we have a typical knife-wound, the behaviour of which is very instructive in illustration of plant-surgery, and may be most easily seen by keeping it in damp air instead of plunging it into sand or soil.
All the living cells actually cut or bruised turn brown and die as before; those beneath - e.g. the living pith, medullary rays, cambium, phloem, and cortex, grow out under the released pressure and form a callus, the outermost layer of which becomes cork, while those below, abundantly supplied with food-materials, proceed to spread, as if flowing over the surface of the cut wood, and rapidly occlude the wound. Meanwhile new roots are formed adventitiously from the cambium just above the plane of section, and push out through the cortex into the damp air, and if the cutting had been in soil it would now be capable of independent existence. It is important to keep cuttings upright, as the roots only spring from the lower end. Such cuttings can be obtained not only from stems, but also from roots and even leaves.