NATURE OF DISEASE. 123 



grow longer, pushing up the dead debris, and 

 divide across by walls parallel to the plane of the 

 wound, and so fornm series of tabular cells with 

 thin walls, which also soon turn brown and die, 

 the cell-walls meanwhile undergoing changes which 

 convert them into cork. The living cells deeper 

 down are now shut off from the outer world by a 

 skin, of several layers, of cork-cells, which prevent 

 the further free access of air or moisture. During 

 the period of active cell-division which initiates the 

 cork, the temperature of the growing cells rises : 

 a sort of fever (wound-fever) is induced, evidently 

 owing to the active respiration of the growing 

 cells. 



This healing by cork occurs in any tissue of 

 living cells exposed b}- a cut leaf-tissue, young 

 stem or root, fruit, cambium, etc. ; and the same 

 applies to any other kind of cutting or tearing 

 injury such as a prick with a needle or the 

 proboscis of an insect, a stripping, or even a bruise. 



Such healing is prepared for and carried out 

 very thoroughly in the case of falling leaves and 

 cast branches, the plane of separation being 

 covered by a cicatrix of cork. 



If the cell-tissue under the wound is actually 

 growing at the time, however, a further process 

 is observed when the wound-cork has been 

 formed. The uninjured cells below go on 

 growing outwards more vigorously than ever, 

 the pressure of the overlying tissues taken off 

 by the cut having been removed, and, lifting 

 up the cork-layer as they do so, they rapidly 



