234 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



solution was recommended, and these measures were at once 

 carried out and resulted in the eradication of the disease. 



In order to deal with a disease in the most effective manner, 

 and at the same time with a minimum of expense, it is essential 

 that the life-history and habits of the causal organism should be 

 fully known. There is obviously a great waste, both of labour 

 and materials, if spraying is undertaken at a time when the 

 organism is in such a resistant condition that it is not affected 

 by the fungicide employed, and the destruction of only a portion 

 of the fungus, however carefully carried out, will never lead to 

 the complete extinction of the disease. The latter statement is 

 particularly applicable to the diseases produced by the various 

 species of Rosellinia. In these the destruction of the obvious 

 part of the fungus, i.e. the perithecia and mycelium on the 

 dead plants, is not sufficient, and unless the mycelial strands in 

 the soil are destroyed at the same time the disease will not be 

 eradicated. The knowledge that fungi belonging to the genus 

 Rosellinia do possess a means by which infection can be carried 

 through the soil is essential in order to ensure the complete 

 eradication of the disease. The history of the outbreak of 

 Rosellinia on the spruce in Scotland affords convincing evidence 

 of the value of expert advice in dealing with the fungous 

 diseases of plants. 



Little can be said regarding the origin of the disease. 

 Rosellinia aquila has not been often recorded in Scotland, and it 

 is possible that the species may have been introduced by some 

 means into the district where the outbreak occurred. Consider- 

 able quantities of spruce seed are imported from the Continent, 

 and the spores of the fungus may have been brought in on the 

 seed. Whatever the origin may have been, the methods 

 employed in dealing with the outbreak proved to be so efficient 

 that there has been no indication of the spread of the disease in 

 the district, and, as far as can be ascertained, there has been no 

 other instance of its occurrence in this country. 



I am indebted to Dr A. W. Borthwick for the photographs 

 shown in the Plates. 



