On the Potato Disease . 195 



first to show manifestations, in the other more likely the tops. 

 When the petals of the flowers themselves are the first to be 

 attacked we may feel almost certain that air-infection has 

 occurred. 



Infection of the flower itself is not a very common occur- 

 rence, but in years gone by the writer has collected several 

 examples of it and has had sketches made. Two of these 

 are copied in the appended illustrations. These show the 

 flowers and their footstalks withered and black. The black- 

 ness in each instance ends abruptly at a certain distance 

 down the stalk, showing that the fungus was advancing 

 downwards and proving also, perhaps, that in some instances 

 its advance may be limited. In fig. 2 it will be seen that 

 one flower remains quite healthy and that even in one and 

 the same flower certain petals may remain healthy whilst 

 others are shrivelled. During the present season but few 

 examples of petal-infection have been gathered, but in one 

 instance the entire head with all the footstalks and the 

 stem for two inches downwards was found black and dry, 

 whilst immediately below the dead portion the stem remained 

 as thick and fleshy as ever and quite green. (See additional 

 statements, page 225.) 



Thus far, beyond implying that a diseased " set " may 

 infect the growing stem and send up its fungus threads 

 to flower out in the leaves, we have said nothing as to the 

 tubers. This, for the cultivator, is the all-important matter. 

 The well-known fact is that the tubers from diseased plants 

 are liable to decay soon after they are taken out of the earth. 

 This is the " potato rot " which caused the famine in Ireland, 

 and which has since been every year very prejudicial to our 

 food-supply. How does the fungus get into the tubers ? That 

 is the most urgent question. There can be little doubt that 

 when the leaves and stem are affected the fungus may grow 

 downwards and so reach the tuber. It is, also, of course, 

 possible that the tubers might be directly infected by zoospores 

 present in the soil. This probably does occur to a certain 



