FUNGOID PESTS OF CULTIVATED PLANTS. 



141 



which the sporules are free in the receptacles (18 x 2 /.i), but the precise 

 nature of their relationship is not distinctly known. 



Sacc. Syll. i. 1590 ; Cooke Hdbk. No. 2736 ; Tubeuf, Dis. 224. 



The above is not common enough or harmful enough to cause the 

 least anxiety. 



Root Fungi. 



It has been known for the past fifty years — and Berkeley was con- 

 tinually reverting to it, and asserting it, in the pages of the Gardeners' 

 Chronicle — that the white fleecy mycelium often seen about the roots of 

 orchard trees was injurious to them ; that it originated from dead stumps 

 and buried wood, and attacked the roots of living trees when it was no 



Fig. 19. — Tree-root Rot (Armillaria mellea). 



longer a saprophyte, but became a parasite and crept up between the 

 cortex and the wood, and ultimately killed the tree. This is now more 

 generally acknowledged to be true, whatever the ultimate development of 

 the mycelium might be, possibly some Agaric, and that dead wood and 

 dead roots left in the soil when young trees are planted will sooner or 

 later prove the source of great injury and destruction. It has been left 

 to more recent- times to demonstrate that mycelium which originally, and 

 in ordinary cases, was only a saprophyte could under favourable con- 

 ditions become a dangerous parasite. 



Under such circumstances it will be seen that trees should never be 

 planted in soil which contains the remains of dead stumps or dead roots, 

 and whenever growing trees are discovered with this mycelium at the 

 roots they should be removed and the soil sterilised before it is planted 



