PATHOLOGIC PLANT ANATOMY 383 



Wound-cork 



Injury to different plant organs such as roots, tubers, rhizomes, 

 stems, leaves and inflorescences is followed by the formation of cells 

 in rows and adjacent to the place of injury. The walls of these new 

 cells react to sulphuric acid, chlor-iodide of zinc and Sudan III and the 

 application of such reagents demonstrates the formation of cork, 

 which has been termed wound-cork. It is developed generally on all 

 parts of the wound, and at its edges connects directly with the normal 

 membranes, thus closing the wound. The walls of wound-cork cells 

 are always thin and are often folded, and the cork cells thus formed are 

 larger than those of the phelloderm. A stem wounded by a knife cut 

 soon heals up unless disturbed. The cut cells die, while those next 

 below grow out as a result of the decreased pressure, giving rise to cork 

 cells. As the opposing cushions of callus close together, this cork is 

 squeezed between them and finally a shearing of the cork cells results 

 as the tips of callus close together and unite. The only external sign 

 of the wound is a slight ridge-like elevation beneath which are traces 

 of the dead cells and the cork trapped here and there beneath the ridge. 

 Normally, wound-cork closes over the broken surface of the scars 

 formed in the autumn by the faU of the leaf, which is actually occasioned 

 by the formation of a cork layer, which cuts off the leaf from the stem. 



