274 TIMBER AND SOME OF ITS DISEASES [chap. 



to fall prostrate on the surface of the soil ; in yet 

 others, the lower parts of the stem of the older seed- 

 ling may be blackened, and daik flecks appear on 

 the cotyledons and young leaves, which may also 

 turn brown and shrivel up (Fig. 42). 



If the weather is moist — e,g. during a rainy May or 

 June — the disease may be observed spreading rapidly 

 from a given centre or centres, in ever-widening circles. 

 It has also been noticed that if a moving body passes 

 across a diseased patch into the neighbouring healthy 

 seedlings, the disease in a few hours is observed 

 spreading in its track. It has also been found that if 

 seeds are again sown in the following season in a 

 seed-bed which had previously contained many of 

 the above diseased seedlings, the new seedlings will 

 inevitably be killed by this *' damping off." As we 

 shall see shortly, this is because the resting spores of 

 the fungus remain dormant in the soil after the death 

 of the seedlings. 



In other words, the disease is infectious, and spreads 

 centrifugally from one diseased seedling to another, 

 or from one ci'op to another : if the weather is moist 

 and warm — *' muggy," as it is often termed — such as 

 often occurs in the cloudy days of a wet May or June, 

 the spread of the disease may be so rapid that every 

 plant in the bed is infected in the course of two or 



