PLANT DISEASES. 



735 



small dark scales ; stem 4-6 inches long, yellowish, and with a distinct 

 ring or ruffle surrounding it near the gills. So far as reproduction by 

 spores is concerned, this fungus is a wound-parasite. In gardens and 

 pleasure-grounds the necessary wounds are too frequently due to careless 

 management of the grass-cutting machine. Such wounding should be 

 avoided as much as possible, and when done should be protected with 

 gas-tar. In woods and pastures, wounds at the base of the trunk or on 

 exposed roots are made by rabbits, hares, mice, &c. When the mycelium 

 has once gained an entrance into the root or base of the trunk, it forms 

 a compact white membrane of interwoven mycelium, which extends 

 between the bark and the wood, thus killing the cambium. The disease 

 passes from one root to another and also ascends the trunk. Eventually 



Fig. 309. — Tree-root Kot {Agaricus mclleus). 



A cluster of the fungus showing the cord-like rhizomorphs, which travel under- 

 ground and attack the roots of living trees of various kinds ; one quarter natural size. 



the white mycelium gives origin to numerous blackish cord-like strands 

 called rhizomorphs, which grow upwards between the wood and the bark, 

 finally killing the tree. These stout black interwoven strands or 

 rhizomorphs, so frequently present between the wood and the bark of 

 decayed fallen trees, must be familiar to everyone. They signify that 

 the tree was killed by Annillaria mellea. 



Numerous black rhizomorphs are also formed in the ground round the 

 base of a diseased tree ; these spread in the soil in all directions, feeding 

 on the humus present, and increasing without limit in length, but not 

 penetrating more than a few inches below the surface. If a rhizomorph, 

 during its progress through the soil, happens to come in contact with the 

 living root of a tree it is capable of attacking, it enters the root, and thus 



