20 



PROTECTION OF PLANTS, 1921-22 



under the bark, from there working inwards. An examination of hundreds of 

 affected trees has failed to substantiate this view in any one instance. On the 

 contrary, in hving trees the fungus enters through wounds or broken or dead 

 stubs and penetrates to the inner sapwood and heartwood, rapidly spreading 

 up and down in these regions of the stem and more slowly outward towards 

 the bark. In birch it appears to spread more abundantly and rapidly in the 

 inner sapwood, but it is important to note that the adjoining heartwood is also 

 affected and in consequence weakened. One of the most significant features 

 is the circumstance that cured timber from trees in which the decay is in its 



Fig. 4. — -A section of yellow birch attacked by Fo77ies Jomentarius. The 

 section was placed for some days in a moist chamber. A strong develop- 

 ment of the mycelium, which darkened in time, appeared as indicated 

 in the blackened zone of the photograph. 



incipient stages is indistinguishable by ordinary means of examination at the 

 ccmmand of the user, from perfectly sound timber. The infection of the birch 

 appears to be commonly associated with the breaking of the branches of the 

 crown due to the action of a boring insect. {Fig. 4). 

 (c) Butt and heart rots. 



Butt and heart rots constitute the outstanding destructive agencies at 

 work in our forests. No forest is exempt, and every mature stand becomes 

 more and more susceptible with increasing age. The time inevitably comes 

 when they bring about an accelerated loss of stumpage values through deterio- 

 ration. They are also responsible for most wind-falls and consequently for 



