S. G. Paine 207 



of the cap. The patches become sliglitly depressed, dry up and crack 

 radially as the mushroom grows. They arise at or near the margin of the 

 mushroom or at the point of contact of one with another, i.e. places at 

 which water is likely to remain for some time after the sprinkling of the 

 bed. At the outset it seemed likely that some micro-organism finds 

 entrance at these spots after multiplying in such standing water. The 

 disease spreads rapidly from one diseased head to others in the same 



Fig. 1. Mushrooms naturally infected, 



cluster in a way which supports the above view as to the mode of 

 dissemination of the disease, the organism presumably being carried 

 by insects or by splashings from infected drops of water during watering. 

 The disease is very superficial; on peeling off the "skin" the under- 

 lying tissue is found to be affected to a depth of, at most, one to three 

 millimetres (the diagrammatic sketch, Fig. 3, shows clearly the slight 

 extent of penetration of the tissue by bacteria, in this case less than 

 half a millimetre), and very frequently is found to be perfectly white 

 and healthy. The affected underlying tissue has a rather water-soaked 

 appearance and a mouse grey or yellowish grey colour. 



14—2 



