354 



Minnesota Plant Diseases. 



FIG. 187. Spores of the apple scab fungus. A. Portion of a section through a scab spot 

 on an apple; b, fungus threads spreading under and lifting the cuticle; a and c, partly 

 disorganized cells of the apple; e, healthy cells of the apple. B. Two spore-bearing 

 stalks giving rise to summer spores. C. Spores germinating. D. Portion of a section 

 through an affected leaf of an apple which has lain on the ground over winter and 

 has given rise to the winter spore stage of the disease; g, spore-case containing a bundle 

 of spore-sacs. E. Two spore-sacs, more highly magnified, each containing eight two- 

 celled winter spores, three of which are shown at F. All highly magnified. After 

 Longyear. 



