292 Studies in Forestry [CHAP. xm. 



short side-branches through the cell-walls into the inside, in 

 search of nourishment. 



When the mycelial filaments come in contact with the starch 

 contained in the cells, this becomes transformed into turpentine, 

 which collects on the inner wall and saturates the tissue itself, 

 so that a process of resinification or inspissation of turpentine 

 sets in and interrupts the circulation of sap throughout the 

 portions affected. These not only extend far up and down the 

 stem, but also reach to a depth of three to four inches in large 

 stems. As the mycelium annually increases in size, the can- 

 kerous parts clogged with resin also increase ; whilst the stems 

 assume an eccentric form of growth owing to increment taking 

 place only where the bark is not yet infected. Sometimes the 

 upper portion of the crown is killed off within a year, when 

 infection has taken place nearly all the way round the stem ; 

 but at other times decades sometimes pass before the crown 

 becomes dry and death ensues. Warm, dry summers favour 

 the advances of the disease owing to the stimulus given to 

 transpiration through the foliage, with which the partial sup- 

 plies of sap yielded by the uninfected portion of the stem 

 cannot maintain a due balance. 



The spores scattered by the aeridia have a change of genera- 

 tion with Coleosporium senecionis, having species of Senecio as 

 their host. The mycelium hibernates on these, and in the 

 following spring develops new spores by means of which the 

 canker of the Pine is produced. 



When once this disease has been noticed, the best measures 

 adoptable are to cut out all the stems attacked before the 

 fungus has had time to develop fully, and to destroy, so far as 

 possible, all two-year old species of Senecio before they flower 

 in April ; this must be done by rooting them out, otherwise 

 the stalks removed are replaced by new stool-shoots. 



3. Caeoma pinitorquum, de Bary, the Pine-shoot Fungus. 

 This fungus is mostly to be found on Scots and Weymouth 

 Pines of from one to ten years of age, although young crops 



