W. MCRAE 



265 



There still remains to be discussed what measures meantime may be taken 

 to check and prevent bark-rot. In untreated cases, where the rot has sunk 

 as deep as to the cambium, the piece should be cleanly excised and the wound 

 carefully painted with tar and tallow. The excised portions must be burnt, 

 and knives sterilized by dipping in an antiseptic solution, e.g., 1 per cent, 

 formalin. In certain areas of the district, practically those in which rainfall 

 is not excessive, and where bark-rot is not a pressing menace, it has been found 

 sufficient to tap less deeply when bark-rot begins to appear, and if that is not 

 enough, to stop tapping for a few weeks. This is usually quite sufficient and 

 no further trouble occurs. The underlying cortex cuts off the infected piece of 

 bark which ultimately scales off. In other parts of the district this is not 

 enough, and recourse is had to smearing the tapped surface ^vith a mixture of 

 tar and tallow. This is done as a preventive on blocks where experience has 

 shown that bark-rot occurs, and its use has proved successful. Enough tallow 

 is melted with tar, so that when cold, the mixture is a paste and not a hquid. 

 It can be carried round in any suitable vessel by the coolie, who puts a thin 

 smear on the renewing bark just above the tapped surface with his thumb or 

 with a piece of gunny, and the consistency of the paste makes it easy to handle, 

 a'ud prevents it running down over the tiapping cut. A v«ry little tar in 

 cultural media inhibits the growth of the fungus. Concentrations of 0*5 per 

 cent, or more of tar in a Quaker-oats-agar medium on which the fungus grows 

 well completely prevent growth, while lower concentrations as far as 0"1 per 

 cent, do not prevent growth in every case. 



This particular experiment was carried on for a month, and the fungus 

 made a copious mycelial growth in the Quaker-oats-agar medium to which no 

 tar had been added, and in no case where the fungus grew in low concentrations 

 of tar in the same medium was the growth anything hke as good. I think 

 it is both the water-proofing and the fungicidal qualities of the mixture 

 that come into play in preventing the fungus from infecting the tree. 

 With izal, one of tho coal-tar products, a sinailar series of experiments 

 waa carried out. 



