ii8 BRITISH GALLS 



result from the stimulus afforded by mites. Whatever the 

 cause, once the growth is initiated, it may continue long 

 after its cause has vanished, and these growths sometimes 

 attain enormous dimensions. In the south of England the 

 majority of the " brooms " on the Birch appear to be caused 

 by mites. Worthington Smith has observed the fungus 

 Exoascus turgidus in connexion with these growths on Birches 

 in Scotland. 



The " witches' brooms " on the Silver Firs {Abies pedmata, 

 etc.) are caused by the fungus at one time known as 

 Perideymium elatinum, the teleutospore form of which occurs 

 on Chickweeds (Cerastium) ; it is the Melampsora cerastU. 

 The mycelium is perennial in the bark, cambium, and stem 

 wood, causing excessive localized hypertrophy. From the 

 top of the fusiform swelling the twigs grow almost vertically 

 upwards. Plate XVII. shows a dead branch bearing an 

 old " broom " ; such may be commonly found beneath trees 

 afflicted by this fungus. The leaves on these twigs are 

 smaller and arranged in a spiral manner ; the orange 

 pustules containing the spores of the fungus appear on 

 them. These " brooms " are never so dense as those which 

 occur on the Birch. The majority of " brooms " produce 

 atrophied leaves only, but in some cases the leaves are 

 normal, and even flowers are produced on the twigs. A 

 " witch's broom " from a Larch was brought to the 

 Haslemere Museum in 1905. The twigs formed a com- 

 pact mass; upon the outermost well-grown leaves were 

 present ; there were also male and female flowers, and near 

 the centre were many old cones that had not been shed. 

 No trace of a parasite, either fungus or insect, could be 

 discerned. The structure was of enormous size and weight, 

 and probably had lived through two decades. Connold 

 alludes to a "broom" on the Horse Chestnut; similar 

 growths occur on Oak, Ash, Beech, Hazel, Blackthorn, etc. 



The somewhat rare phenomenon of metamorphosis of the 

 floral leaves is seen in an extreme form in the elongated, 

 thin, and twisted purple-red lobes which occasionally take 



