150 



THE CULTIVATED EVERGREENS 



This is due to the fact that the conditions for the spreading of 

 the causal fungi are ideal in the forest, but are much less 

 favorable outside of these domains. Most of the fungi causing 



these wood-rots are on one general 

 type commonly known as 

 "bracket-fungi" or "polypores." 

 One of the toadstools {Armillaria 

 mellea), however, is responsible 

 for an important root-rot, not 

 only of conifers but also of a 

 great variety of other trees and 

 even of herbaceous plants. 



The wood may be attacked in 

 various ways. The heart wood 

 alone may be decayed 

 to a greater or less 

 extent. This may take 

 place in the roots, at 

 the butt or higher up 

 in the trunk and 

 branches. In most 

 cases, the parts at- 

 tacked are so weakened 

 that the tree is eventually uprooted or broken off by the wind. 

 Less commonly, the sapwood and bark of living trees are also 

 attacked and rotted. In such cases, death of certain parts or 

 of the whole tree may ensue, due to an interference with the 

 passage of food materials. 



Infection takes place through injuries exposing the heart- 

 wood or sapwood, as the case may be. Spores of the fungi 

 concerned, falling on the injured spots, germinate under 

 suitable conditions, producing a small tube which penetrates 



18. Sporophores on trunk of tree. 



