29 



adjacent to the cambium to various parts of the tree. When the tree 

 is girdled or the bark removed no growth takes place below the 

 girdling because the channels of transportation are destroyed. 



In some young plants the pith cells possess the power to form a 

 callus, but such cases are rare and of little importance. The younger 

 the tissue or organ the more quickly it will heal, providing other 

 things are favorable, and vigorous trees will form a callus much more 

 quickly than old or weak ones. The nearer wounds are to the plas- 

 tic materials the more rapidly they will heal ; for example, the upper 

 part and sides of a cut as a rule heal the most rapidly because they 

 are in more direct contact with the channels supplying plastic ma- 

 terials for healing. (See Fig. 7.) Cuts made near large leafy branches 

 are more likely to heal quickly than those near small ones, for the 

 reason that a larger amount of the plastic materials is available. 



To facilitate healing, recourse is occasionally made to cutting the 

 bark smooth around the stumps of the re- 

 moved limbs, and it is also claimed that after 

 the callus is well started a re-cutting of the 

 surface stimulates it to grow faster. Moisture 

 is said to stimulate the growth of the callus, 

 and the old practice of covering the wound 

 with a mixture of cow-manure, clay and lime 

 has this object in view. 



In the pine family, whenever a wound is 

 made it is quickly covered with pitch, one of 

 the best substances for covering wounds, but 

 for practical purposes coal tar is cheaper, and 

 a thick coat of paint answers the purpose 

 quite well. 



Thick shellac dissolved in denatured alco- 

 hol has been recommended for painting 

 wounds, and might be used to advantage. 

 Coal tar is likely to injure delicate tissue, although this injury is not 

 permanent. When paint and other substances are applied to limbs 

 when they are moist and show a tendency to bleed, the results are 

 not always satisfactory, and cases have been known of decay occur- 

 ring even when coal tar has been used. The principal object in 

 painting exposed wounds is to prevent the entrance of destructive 

 organisms, and particular care should be exercised in doing it. 



Fig. S. Girdling by ciiain 

 placed around tree. 



From " Park and Ceme- 

 tery." 



