Bui. 957, U. S. Dept. of Agriculture. 



Plate II. 



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Sections of Pine Trees, Showing Typical Progress of Blister- 

 Rust Infection. 



Fic. 1. — Soction of the Irimk ofa yoiiiiji Iroo of Ti h us s^roftus, showinp; entrance of t ho 

 blister rust into the trunk from an earlier infected branch. The dark .^Jliadins; on tha 

 trunk indicates the visibly infected portion. X 1. Drawn by .1. M. Shull. Fig. 2. — 

 I'ruiik i)( yoiinR tree of Pinus strobiis, abmit 2 inches in diameter, showin;; (bv zona- 

 tion) iho "progress of the lilister rust. The di.sea.se entered the trunk from the side 

 branch. The cracked bark (r) indicates where :i?cia have formed: the black spots (6) 

 indicate the developinj; pvcnia: tlie sliaded part outside (a) indicates the area where 

 the bark is discolored, "x !>. Drawn by K. H. Colley. Fig. .i.—\ trunk 8 to 10 

 inches in diameter. The disease attacked the swollen t'wip first, then ran downward 

 to the main branch, from which ii has spread into the trunk. The latter will soon 

 be girdled and the tree will die. I'hotograiihed by J. F. Collins. 



