DISEASES OF FOLIAGE, ETC. 39 



swellings comes off in flakes, revealing a bright orange- 

 yellow powdery coating, partly covered by a thin white 

 film. The same orange-yellow powder consisting of 

 spores escapes from small bladder-like pockets with a 

 thin white lining, which are conspicuous between the 

 bark cracks of the swelling. The wood in these galls is 

 excessively developed ; the regular channels in the sap- 

 wood through which the water is pumped up beyond the 

 galls are disturbed, and the water flow ceases. The liv- 

 ing bark is killed and destroyed. As long as the up- 

 ward flow of water in the wood of the branch and the 

 downward flow of food prepared in the needles are not 

 completely stopped, a very rich but temporary develop- 

 ment of foliage beyond the gall may result from the 

 girdling action of the fungus. Such strikingly full and 

 luxuriantly green branches are sometimes very con- 

 spicuous on yellow pine, where, however, they may also 

 be the result of girdling by mistletoe. (See Mistletoes, 

 p. 56.) In time the flow of water and prepared food 

 is cut off, and the branch and needles beyond the 

 gall die. This disease constitutes a serious menace to 

 seedlings and smaller saplings of yellow and Jeffrey 

 pine, frequently killing them in groups. When it 

 attacks the leader it seriously interferes with the 

 normal growth of the young tree. Lodgepole pine, 

 especially in the northern California forests, suffers 

 severely, many seedlings being killed, and trees up to 

 pole age completely stunted, and sometimes killed. The 

 very similar galls on Monterey pine are also caused by 

 a Peridermium (probably P. cerebrum). 



