PLATE 50 

 Cronartium ribicola: 



A. — A figure illustrating the relation of the pycnium (a), the heavy black line at 

 the top, and yottng aecium, to the host tissue. The heavily stained cells (6) in the 

 region of the young aecium are the fertile cells. Compare Plate 54, B. X 125. 



B. — A section through a mature aecium, taken a little to one side of the break in 

 the bark, to show the aeciospore chains (a), the multilayered peridium (6), and the 

 overlying host tissue. X 75. 



C. — A similar section showing a double pycnial layer (a, Oi), and the location of the 

 cork cambium (6) which cuts out the old pycnium. X 40. 



