TREES AND TIMBER 



447 



the spores. This is the cluster-cup stage of a rust which 

 appears later in the season upon goldenrods and asters. 



Red rot^ (Polyporus ponderosus 

 von Schrenk). — Upon dead trees 

 this rot starts just under the bark, 

 usually near the tree top, often fol- 

 lowing " bluing." The wood is at 

 first wet and soggy, but soon becoxiies 

 brittle, so that it crumbles readily. 

 The cracks become filled with felted 

 fungous threads. The sporophores 

 first appear as fleshy knots, soon red, 

 which widen to pore-bearing shelves. 



Cladosporiose blight (Cladosporium 

 herbarum (Pers.) Link). — The ter- 

 minal leaflets die and curl and the tip 

 of the stem is killed. Dark patches 

 of hyphse appear upon the dead parts. 



POPLAR 



Rust {Melampsora populina (Jcq.) 

 Lev.). — This is similar to willow rust. 

 See p. 450. 



Powdery mildew, uncinulose. See 

 willow. 



Leaf blight, marsoniose (Marsonia 

 Populi (Lib.) Sacc). — Primary in- 

 fection occurs upon the leaves, re- 

 sulting in small, 3-8 mm., circular, black dead spots which 

 are quite definitely bordered. As the leaves die, patches 



' von Schrenk, H., U.S. Dept. Agr. Bur. Plant Indus. Bui. 36, 1903. 



Fig. 194. — Pine needle 



bearing cluster cup of 



rust, enlarged. After 

 Clinton. 



