BRITISH GALLS 
118 
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 (Abiespectinata, 
etc.) are caused by the fungus at one time known as 
Peridermiuni elatinum , the teleutospore form of which occurs 
on Chickweeds ( Cerastium ); it is the Melampsova cerastii. 
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 
