7IO FUNGI 



present is attributed to the fungus Oospora scabies Thaxter, 

 known only in the conidial state. The hyphae are very short and 

 slender, and give rise to chains of small oval conidia ; the scabs 

 are somewhat greyish in appearance when the fungus is abundant. 



Closely resembling this is a scab, said by Roze to be due to 

 the attack of a Micrococcus. 



(ii) Another form in which there is a development of corky 

 tissue in somewhat larger patches is brought about by the 

 parasitic action of Spongospora scabies Mass., an organism be- 

 longing to the M)xomycetes or slime-fungi. 



(iii) In some cases the trouble appears to arise from the 

 application of lime, ashes, or alkaline dung to the soil. 



(iv) The millipedes Julus pulchellus and J. terrestris take 

 advantage of any damaged area on the skin of the potato, and 

 increase the wound by eating deeper into the healthy part ; a 

 scabbed appearance results. 



' Scabby ' potatoes should not be used for sets, and ground on 

 which ' scabbed ' crops have been raised should not be planted 

 with potatoes for some time. 



Where the disease is prevalent, dressing the tubers before 

 planting with dilute solutions of corrosive sublimate (mercuric 

 chloride) has been found very beneficial. 



One ounce of corrosive sublimate should be dissolved in two 

 gallons of hot water in a barrel or other wooden vessel, and 

 allowed to stand all night. In the morning add eight gallons 

 of water, so as to make up the whole solution to ten gallons. 

 Then place the ' seed ' tubers to be treated in a coarse sack and 

 suspend or soak the whole for an hour and a half in the liquid. 

 After drying, the potatoes may be planted. The same solution 

 may be used a number of rimes. 



Corrosive sublimate is a most powerful poison, and great care 

 is needed when dealing with the pure substance or strong solutions 

 of it. 



Soaking the 'seed' tubers for an hour in weak Bordeaux 

 mixture (p. 700) is said to be a useful method of diminishing 

 the disease. 



(5) Potato 'Wart.' — This disease, sometimes erroneously 

 termed 'Black Scab,' was first noticed in Hungary in 1896, and 

 since then has become very prevalent in many parts of England 

 during the last five or six years, and has occurred in Scotland 

 and Ireland. 



