88 HEART-ROT 



across a number of annual rings and even reach the cambium 

 when the attack is more marked on one side. This may 

 specially be seen in a rootstock when the fungus has entered 

 the tree through a lateral root. 



Owing to this red colour the earlier stages of the disease 

 are sometimes known by foresters under the name of ' red 

 rot'. 



The red colour is ascribed by Hartig to infiltration of 

 the wood by turpentine and resin, which are secreted by the 

 resin ducts and medullary rays. If shavings of the red 

 wood are soaked for a considerable time in methylated 

 spirit, the turpentine and resin are dissolved and the colour 

 disappears, except in the medullary rays which retain 

 a reddish-brown tinge. Osmic acid stains part of the con- 

 tents of these medullary rays a deep black, and it is probably 

 the proteins which both give this reaction and cause the 

 red-brown colour in these cells. In the specimens that 

 I have examined the medullary ray cells have been all dead 

 and no nuclei could be traced. Stray hyphae were often 

 found in the red rot region, and where hyphae could not be 

 seen the occurrence of the empty bore-holes proved that they 

 had formerly been present. Hyphae were even seen in the 

 normal coloured wood outside the turpentine region. 



(ii) Soluble gum. During the red rot and earlier stages of 

 attack a large amount of soluble gum is present in the 

 tracheides and medullary rays. It can easily be seen in 

 microscopic sections mounted in alcohol, in which it takes 

 the form of an emulsion in the tissues. On addition of 

 water this vanishes. It may be extracted by soaking in 

 water shavings of wood, which has reached the red rot 

 stage. When the water is poured off and filtered, it is 

 found to be slightly opalescent, and on adding an excess of 

 alcohol the gum is thrown down as a flocculent precipitate. 

 This may be collected by filtering, and on drying the filter- 

 papers it remains as a yellowish mass. This is readily 

 soluble in water, so that a strong and moderately pure 

 solution may be obtained in this way. From 600 grm. of 

 red rot shavings I obtained 22 grm. of gum. When dry it 



