PLATE 54 

 Cronartiiim ribicola: 



A. — A drawing of an infected 12-year-old main stem. The infection entered the 

 main stem along the small branch, the stub of which is shown at the right of the figure. 

 a, The advancing edge of the infection; b, the pycnial area. The black dots are the 

 pycnial spots; c, the aecial area on which the bark is cracked and broken. In another 

 season the aecial area would spread over the pycnial area {b), and the pycnial area 

 would be advanced as far as the botmdary (a) tmder normal conditions. The boundary 

 (a) would be proportionately advanced also. The specimen from which the drawing 

 was made was collected in August, 1917. X >2- 



B. — Drawing of a section through part of a young secium showing the relation of the 

 fertile cells with their denser protoplasmic contents to the overlying sterile cells, in 

 which the cytoplasm and nuclei have begtm to go to pieces. The manner in which 

 the adjacent host cells are forced apart by the fxmgus cells is also shown, dc, decom- 

 position products in the host cells; he, host cell wall; sc, sterile cells; /c, fertile cells; 

 h, haustorium. The elliptical bodies in the host cells represent starch grains. X 400. 



