FUNGI 21 



Certain especially destructive forms of fungi are capable 

 of living and extending in a vegetative manner in the soil, 

 and are consequently combated with great difficulty. Such 

 fungi are unfortunately equally capable of becoming true 

 parasites when the mycelium comes in contact with the 

 roots of living plants, and possess the further distinctly 

 objectionable peculiarity, from the human standpoint, of 

 not being so fastidious in their choice of a host as is 

 customary with fungi, but attack, almost indiscriminately, 

 every plant that comes in their way. Among such may 

 be enumerated white root-rot (Dematophora necatrix\ 

 New Zealand root-rot (Rosellinia radiciperda\ tree root- 

 rot (Armillaria mellea), conifer root-rot (Fomes annosus\ 

 and various others. 



Where rotting of the roots of trees is caused by fungi that 

 extend their range by means of mycelium spreading in the 

 soil, it is advisable^ as suggested by Hartig, to isolate such 

 diseased trees by a narrow trench about eight inches deep, 

 making the trench sufficiently distant from the trunk so as to 

 be outside the spread of the roots. Throiu the soil removed 

 inside the trench. 



Many parasitic fungi can only live on one particular 

 host-plant, and the majority are confined in their ravages 

 to closely related plants, or at most to plants belonging 

 to the same Order. Hence a disease spreads quickly when 

 numerous plants of the same kind grow in close proximity, 

 whereas when the vegetation is of ^. mixed character, those 

 plants not susceptible of the disease intercept numerous 

 spores, and thus to a great extent protect the susceptible 

 plants. 



