WEEDS AND FUNGI 133 



It causes the silver fir canker and * witches'-broom '. The 

 shoots attacked become brush-like and erect, and are of an 

 entirely different appearance from the ordinary shoots. Such 

 abnormal growths are called the witches'-broom. The myce- 

 lium grows in the bast, causing a swollen canker on which the 

 bark is deeply cracked. Should the fungus attack a part 

 where there is no living bud, a canker is formed but not the 

 witches'-broom. The fructifications are orange-coloured, and 

 appear on the under side of the leaves of the witches'-broom. 

 They give out their spores in June, and the needles then die. 

 The witches'-broom lives about sixteen years, and branches 

 freely, somewhat resembling a bunch of mistletoe. It then 

 dies, and only the canker remains. 



Badly cankered trees may die outright, but more often they 

 live on, the timber however being spoilt. 



The best preventive measures are to prune off branches 

 affected in June and July before the spores ripen, close to the 

 stem, tarring the wounds. Cankered stems should be cut out 

 in the thinnings. 



The larch canker (Dasyscypha calycina or Peziza Wilkommii). 



This fungus is without doubt the most destructive one 

 found in British woods and has done an enormous amount 

 of damage. It is found in almost every young larch wood 

 in England, Scotland, and Wales, but fortunately it is less 

 common in Ireland, especially in mixed woods. 



The disease is recognized by the appearance of swellings 

 on the stem and branches ; the bark splits, turpentine flows 

 out, and the wood is often exposed. In the cracks round the 

 swelling, cup-shaped fructifications, about the size of a large 

 pin's head, appear; these are white outside and orange yellow 

 within the cup. When the weather is damp these produce 

 spores which infect other trees. As time goes on the canker 

 increases in size, and becomes black and spoon-shaped. It 

 gradually spreads round the stem, and may finally kill the 



