ARTIFICIAL WOUNDS. 199 



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. 



Callus-formation is not confined to the basal 

 end of a cutting; it has nothing to do with 

 position, but is a reaction to the wound stimuli, 

 independent of light, gravitation, etc. As time 

 goes on, however, the internal organisation of the 

 erect cutting usually reacts on the callus at either 

 end, and roots only rise from the lower one, while 

 shoot-buds may form in the upper one, though it 

 is possible to bring about the formation of buds 

 from the lower end also. 



Branch stumps. A more complex example is 

 furnished by a branch cut off short some distance 

 say a foot from the base, where it springs from 

 the trunk. As before, the immediate effect of the 



