PLATE 48 

 Cronartium ribicola on Pinus strobus: 



A. — This figure illustrates the etiolated condition of the bark in the case of a com- 

 paratively young nodal infection. The node lies between 4- and 5-year-old wood. 

 The infection originated on the opposite side of the stem to that shown in the photo- 

 graph. Note the irregular margin of the etiolated area. The mycelium, starting in 

 opposite directions from the infection point, has now completely encircled the stem. 

 The jimction point of the encircling hyphse is along the line ab. Natural size. 



B. — This figure illustrates an intemodal infection, somewhat older than that shown 

 in figure A, in which the infection apparently originated at the base of the leaf fas- 

 cicle (a). The darker patches on the pronounced canker area are pycnial spots, 

 ^cia are formed under the bark all over the canker and are beginning to break out 

 toward the upper etfd. Note the characteristic shape of the young canker. Natural 



size. 



(660) 



