288 MANUAL OF TREE DISEASES 



witches'-brooms are formed. The smaller branches and twigs 

 are infected through injuries in the bark and abrupt globose 

 or gradual spindle-shaped swellings are produced. The globose 

 type of gall is found more commonly on scrub, jack, short-leaf, 

 lodge-pole, sand, Pinon, Norway and spruce pine, while the 

 more gradual swellings are found on Coulter, western yellow, 

 Monterey, gray, loblolly and pond pine. When the swelling 

 originates at the base of a branch, the adjacent tissue of the 

 trunk is affected and large burls are formed. The part of the 

 tree above these enlargements of the trunk and branches is 

 ultimately killed. A single tree may have from one to hundreds 

 of galls and several witches'-brooms. Young seedlings are 

 often affected and killed. 



The fungus fruits abundantly in the spring by forming 

 prominent yellowish blisters over the surface of the globose or 

 spindle-shaped swellings. These are united into continuous 

 convoluted ridges which resemble the appearance of brain- 

 tissue. The covering of the blisters is broken and a large 

 quantity of orange-colored powder dusts out and is blown away 

 by the wind. 



The leaves of many species of oaks are affected by the same 

 fungus. During the summer, small yellowish or reddish 

 pustules are formed on the under sides of the leaves. Later 

 from the same pustules numerous brown bristles are pushed 

 out. The leaves of the oak are not appreciably injured by the 

 fungus. 



Cause. 



This blister-rust disease is caused by the fungus Crcmartium 

 cerebrum { = Peridermium cerebrum, P.fusiforme and the Pacific 

 Coast form of P. Harhnessii). The fungi causing the blister- 

 rusts of pines are closely related species having similar life 

 histories. The life history of the white pine blister-rust fungus 

 (page 279) serves equally well for this species with the excep- 



