856 



Root Injuries. 



Having thoroughly discussed the overgrowth processes of the aerial 

 axis after all kinds of injury, we can quickly summarize the healing of root 

 wounds. They correspond with those of the aerial axis and undergo modi- 

 fications only inasmuch as the surrounding medium often interferes with the 

 process of overgrowth. For example, if the soil is very moist, the stage of 

 callus formation is prolonged, the transformation of the callus tissue to the 



liniuT overgrowth edge is slower and 



the possibility of infection by wood de- 

 stroying fungi greater. These factors, 

 however, become less significant if the 

 root wound surface is exposed to the air. 

 The influence of light, warmth and dry- 

 ness promotes the closing of the wound 

 and removes any far-reaching influence, 

 from even large wound surfaces, on the 

 condition of health of the whole root. 

 The best proof is found in much fre- 

 quented forests in the \icinity of large 

 cities where the superficial roots are 

 constantly rubbed bare by pedestrians 

 and, nevertheless, find opportunity to 

 cover the edges of the wound with over- 

 growth walls. The adjoining figure illus- 

 trates such a root so worn that only the 

 first formed annual rings are found to be 

 still intact on the upper side. A cross 

 section shows that no {)arasitic wound 

 decay has occurred at the wounded 

 place; the wood of the lower side is 

 sound. 



The wounds produced in transplant- 

 ing deserve the most consideration. 

 Transplanting is a necessary process, 

 which cannot be omitted in any nursery, 



for trade rec|uires the delivery to the purchaser of trees which, after trans- 

 portation to a permanent place, exhibit the greatest possible capacity for 

 vigorous growth and development. 



In transplanting older trees with well developed tops and extensive root 

 systems, a cutting ofiF of the larger root-branches cannot be avoided ; hence 

 the great danger of attack by parasitic root decay, which gradually advances 

 into the trunk. But even if this danger has been prevented by the painting 

 of the cut places with tar, the transplanting of old trees is always a danger- 

 ous operation because the activity of the root system is retarded until new 



Fig. 203. A llat-lyinff root of the 

 alder harked by the tread of feet. 



