INTRODUCTION xi 



during stormy weather, effects of lightning, 

 careless felling and removal of timber, the 

 grazing of farm stock, insect attacks, and in 

 the case of lawn and park trees is often trace- 

 able to the mowing machine, horse-roller, or 

 tools of the careless workman. 



Fungi rarely attack healthy trees, but when 

 the bark is injured and the wood exposed they 

 find a suitable medium and quickly bring about 

 a diseased condition which, if not promptly 

 attended to, will, in certain instances at least, 

 result in the death of the affected tree. They 

 vary much in size, from the almost micro- 

 scopical parasites to the beef-steak fungus, 

 which latter, under favourable conditions, will 

 attain to a diameter of two or more feet and 

 occur in groups of a dozen or more, arranged 

 in their curious shelf-like order on the tree 

 stem. It is quite common to find this and 

 another nearly allied species growing on the 

 stems of the elm and oak at a height of thirty 

 or forty feet from the ground, while on the 

 same tree not a specimen can be detected 

 nearer ground level, which points to the fact 

 that the spores are carried to a great height, 



