PESTS. 55 



all parts of the tree except the young branches and the roots. 

 He considers that "the external colour of the bark in places 

 where the canker is present is in many cases different from that 

 of healthy parts, but no actual colour can be given as typical 

 of a canker spot. As a rule it is darker in colour and the surface 

 of the bark somewhat different." ... " The tissue under the 

 outer bark, however, always shows by its colour when there is 

 any considerable quantity of the canker fungus mycelium 

 present. Instead of a bright clear yellow, as is found in the 

 healthy bark of the Para rubber tree when cut, the colour of the 

 cankered tissue recently attacked is of a dirtier yellow or even 

 a neutral tint, and when the fungus has got complete hold the 

 tissue is claret-coloured and not unlike the inside of the fruit 

 wall of a ripe mangosteen. An important fact to be observed 

 is that in those areas invaded by the mycelium of canker fungus 

 no latex will be found at all." 



As with many other fungi Nectria has two reproductive 

 forms, and Carruthers states, with regard to the species under 

 review : " The spores are of two kinds ; the first spores produced, 

 which are called ' Conidiospores,' are of a whitish-grey colour 

 in mass, and look somewhat like thick white mould. Later on, 

 and produced at the same places, pushing their way out from 

 behind the conidiospores, are the perfect fruits of the fungus 

 or perithecia, which are characteristic of the groups Nectria, to 

 which the fungus belongs. They are, when seen with the naked 

 eye, like grains of red pepper, sometimes a mass of them occupy- 

 ing a space as big as a 10 cent piece, or even bigger. When 

 looked at through a lens they will be seen in shape not unlike 

 minute strawberries, some ten to fifteen making a mass about 

 equal in size to a pin's head ; they are roundish with a point 

 when fully formed." The method suggested for combating this 

 disease is the excising away of diseased tissues with a sharp 

 knife and burning them on the spot. As a preventative measure 

 trees in infected districts might be sprayed with Bordeaux 

 mixture, which would render the parts sprayed immune from 

 infection so long as the copper sulphate is present. It would be 

 advisable to keep trees from which diseased parts have been 

 excised under constant observation for a few months, for if 

 any mycelium has been left behind the disease would probably 

 reappear. 



