Bui. 957, U. S. Dept. of Agriculture. 
Plate I 
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Sections of Pine Trees, Showing Typical Progress of Blister- 
Rust Infection. 
Fig. 1.— Section of the trunk of a young tree of Pinus strobus, showing entrance of the 
blister rust into the trunk from an earlier infected branch. The dark shading on the 
trunk indicates the visibly infected portion. XI. Drawn by J. M. Shull. Fig. 2.— 
Trunk of young tree of P'inus strobvs, about 2 inches in diameter, showing (by zona- 
tion) the progress of the blister rust. The disease entered the trunk from the side 
branch. The cracked bark (c) indicates where aecia have formed; the black spots (b) 
indicate the developing pycnia; the shaded part outside (a) indicates the area where 
the bark is discolored. X h Drawn by R. H. Colley. Fig. 3.— A trunk 8 to 10 
inches in diameter. The disease attacked the swollen twig first, then ran downward 
to the main branch, from which it has spread into the trunk. The latter will soon 
be girdled and the tree will die. Photographed bv J. F. Collins. 
