10 



FARMERS' BULLETIN 742. 



They are usually somewhat longer one way than the other. After 

 a few days the outer membrane, which is white in color, breaks open 

 and the top falls off, exposing the bright-yellow, dusty spores within 

 (PI. I, A). These, after a number of weeks, are completely blown 

 out of the cuplike cavities in the bark. The white membrane sur- 





FIG. 5. White-pine tree 4 years old, showing marked swelling caused by the blister rust. The swelling 

 extends out into the branches. No blisters have yet been produced on this tree. (One-fourth natural 

 size.) 



rounding them also disappears, and there remains in the bark merely 

 a rounded hollow, which usually has a whitish, granular appearance 

 within. Th,is is quite characteristic in appearance and, when one 

 becomes familiar with it, is as easily distinguished as are the bright- 

 yellow fruiting bodies themselves. On trees which have been infected 

 when quite young, the disease girdles the main trunk by killing the 



