F. T. Brooks and A. Sharples <>l 



(c) Finally there is the Necator stage which was formerly looked 

 upon as a separate fungus, Necator decretus, Mass., but is now known to 

 be a stage in the life-history of Pink Disease. Pustules of Necator are 

 seen on the left-hand side of Plate XVI, fig. 2. The fungus in this 

 condition consists of orange-red (not pink) pustules about one-eighth 

 inch in diameter, each pustule being a mass of spores which serve to 

 propagate the disease. In our experience the Necator stage has been 

 confined to the side of the branch which is exposed to the brighter 

 light. The Necator stage has always been found by us to be associated 

 with other forms of Pink Disease, and so intimate is the connection 

 between it and the other forms that it is difficult to understand the 

 doubt that formerly existed as to the identity of Necator decretus and 

 Corticium salmonicolor. 



Spores of the fungus germinate on healthy bark especially where 

 there is an accumulation of moisture. The mycelium which develops 

 is entirely superficial at first, but after a time it penetrates the bark. 

 When the mycelium reaches the laticiferous tissues, exudation of latex 

 frequently begins and this runs down the bark and becomes blackened 

 as time goes on. The weeping of latex from branches is often an 

 indication of the presence of Pink Disease when from ground level no 

 other sign of the disease can be seen. Once the mycelium has penetrated 

 the bark it spreads upwards and downwards over and through the bark 

 causing it to rot. The mycelium spreads more rapidly over the bark 

 than through it. The fungus sometimes advances into the wood, this 

 happening more frequently in small branches than in large ones. If the 

 fungus spreads in the wood, the water supply becomes checked and the 

 foliage of the affected branch turns brown and dies. On some undu- 

 lating estates planters discover those trees which are affected by Pink 

 Disease by observing from a hill the branches which are affected in 

 this manner. Further information concerning the presence and develop- 

 ment of the fungus in the wood is given below. Occasionally the fungus 

 spreads downwards so vigorously that the whole of the upper part of the 

 tree dies. In such a case as that represented in Plate XVII, fig. 3, the 

 lower part of the tree sometimes makes an effort to recover by putting 

 out new branches. When large branches are attacked by Corticium 

 salmonicolor the progress of the fungus in the bark may be checked by 

 a spell of dry weather and in this case an open, canker-like wound such 

 as is shown in Plate XVII, fig. 4 is often formed as described by 

 Petch (9). The formation of a callus on the margin of the wound 

 tends to repair the injury and occasionally the disease is entirely 



