PLANT DISEASES DUE TO FUNGI. 47 



Usually the disease spreads over a wider area each year. 

 There are one or two points in connection with the life-history 

 and habits of these fungi which at once point to a remedy, viz. : 



i. They are unable to develop excepting in the presence of an acid. 



ii. They flourish best in sour, badly drained, and poorly aerated 

 soils. 



iii. As the fungus makes use of weeds as food, when a cereal 

 crop is on the land, it is advisable to keep these down. 



iv. All diseased haulms or tubers should be burnt. 



v. Liberal applications of ground unslaked lime will destroy the 

 fungus and sweeten the soil. 



vi. The cessation of all acid manures is advisable. 



vii. All purchased seed should be obtained from dry, elevated 

 districts, and should be carefully examined to see that it is free from 

 the small sclerotia or concentrated masses of mvcelium. 



POTATO LEAF-CURL. 



Macrosporium solani, Cooke. 



In Worcestershire, Warwickshire, Staffordshire and Leicester- 

 shire, there has been a large amount of this disease during the past 

 season. 



The first indication of the disease is the curling of the leaves, 

 followed by the drooping or wilting of the stem. Later a number 

 of minute blackish patches of varying sizes may be observed on the 

 leaves. These are due to the conidia of the fungus. 



If a section is now made of the stem it will be found to contain a 

 dense mass of mycelium, which stops up the water-conducting vessels, 

 thus causing the leaves to curl and the stems to droop. 



As the disease progresses the mycelium passes from the stem into 

 the branches below the surface and into the young tubers. Here the 

 mycelium is said to hybernate ; thus if such tubers are used as " seed " 

 the disease is perpetuated and the new tubers again infected. Tubers 

 produced by diseased plants, if lifted early, are said to be free from 

 the disease. 



