2 28 TRANSACTIONS OF ROYAL SCOTTISH ARBORICULTURAL SOCIETY. 



Rosellinia necatrix (also known as Dematophora necatrix), the 

 white root-rot, which was also described by Hartig, has a 

 somewhat similar life-history to the preceding species. This 

 disease is prevalent in vineyards and orchards on the Continent, 

 but is rare in this country. It attacks a large number of host 

 plants, including young plants of the oak, beech, pine, and 

 spruce. 



Rosellinia aquila, which is the cause of a serious disease of 

 the mulberry on the Continent, also attacks a large number 

 of other trees and has been recorded several times in this 

 country, but merely as a saprophyte. It resembles Rosellinia 

 qiiercina in many respects, but differs in the form of the 

 conidiophore and other characters. The disease is usually 

 found on mature trees. Several diseases caused by other 

 species of Rosellinia have been described in various countries, 

 but do not appear to have been recorded in Britain. 



The various fungi included in the genus Rhizoctonia were 

 associated by Hartig with the species of Rosellinia^ on account 

 of the close similarity of the mycelial strands found in both 

 genera. In Rhizoctonia sclerotia are produced but no re- 

 productive organs are present, and it has been suggested 

 that the forms are merely vegetative conditions of various 

 species of Rosellinia. 



Rolfs ^ has, however, proved in the United States that 

 Rhizoctonia violacea is the vegetative condition of one of the 

 Basidiomycetes, Corticiiim vagum var. solani. The damping-off 

 of coniferous seedlings has been shown in the States to be 

 largely due to this fungus. Hartig ^ has stated that Rhizoctonia 

 violacea attacks the young plants both of hardwood and conifer- 

 ous trees in Germany, but there is no evidence as to the exact 

 relationships of the fungus involved. Somerville,^ in this 

 country, has recorded the attack of Rhizoctonia violacea on 

 plants of Finns silvestris, but it appears that the fungus 

 described was not Corticium vagum but probably belonged to 

 an altogether different group. An attack of R. violacea on 

 4-year-old spruce has been recently described from Silesia,^ 



^ Colorado Agric. Btill., No. 91. 



" Lekrbuch der Pflanzenkrankheiten, Dritte Auflage, 1900, p. 67. 

 •* Quart. Journ. Forestry, vol. 3, 1909, p. 134. 



■* Merker, " Ein neuer Pilzschadling im Fichtenpflanzgarten," Naturw. 

 Zeitschr. Forst-u. Landw., 18, p. 218, 1920. 



