SECTION II 

 WOUNDS 



NUMEROUS wounds are produced annually in plants which are 

 the result of normal biological processes. Thus leaves are shed 

 in autumn, certain twigs are naturally cast off (e.g. in poplars 

 and oaks), and the outer layers of the cortex die. The plant 

 makes preparation some time in advance for all such wounds 

 as occur naturally, so that at the moment when the wound is 

 formed the process of healing may be regarded as completed. 

 This preparation consists in a periderm being formed in the 

 tissues along the plane which the surface of the wound 

 ultimately occupies. In its origin and structure this periderm 

 entirely agrees with the periderm of uninjured shoots, or with 

 the peridermal covering that gradually forms on wounds which 

 have resulted from an accident. In many cases a protective 

 covering of gum is first spread over the wound, and later on the 

 formation of a periderm is gradually accomplished. Only such 

 wounds as are due to external mechanical causes, which have 

 exposed the internal living tissues to the prejudicial influences 

 of the environment, come into the category of pathological 

 phenomena. 



HEALING AND PRODUCTION OF NEW TISSUES IN GENERAL 



In order to understand the processes of healing and the 

 production of new tissues, we must first cast a glance at the 

 different kinds of tissues and their capacity to produce new 

 growths. 



On the young parts of plants the protective covering is 

 represented solely by the epidermis, which usually consists of 

 a single cell-layer. But before this has entirely lost its power 



Q 



