4 BULLETIN 534, U. S. DEPARTMENT OF AGRICULTURE. 



In 1907 Scott and Quaintance (5) described the disease and gave 

 tentative recommendations for its control. 



The first extensive report on the life history of the fungus and the 

 first definite recommendations for its control were published by Scott 

 and Rorer (6) in 1907. Later (1909), by comparison with type speci- 

 mens they identified the fungus definitely as Pkyllosticta solitaria E. 

 and E. and determined by cross inoculations that the fungus found on 

 leaves, fruit, and twigs is identical. They further determined that 

 the fungus passes from one season to another in small cankers on the 

 twigs. 



Sheldon (7) in 1907 reported the presence of the fungus on twigs. 

 He was the first to identify the fungus as Pkyllosticta solitaria E. 

 and E. and gave a good description of the disease on leaves, fruit, 

 and twigs. 



Lewis (3) gave a detailed description of the disease on the fruits 

 of different varieties and noted particularly the destruction of fruit 

 spurs. 



THE FUNGUS. 



The life history of the causal organism has been traced by Scott 

 and Rorer and by Sheldon. They found that the fungus passes the 

 winter alive in the small twig cankers, where it grows and develops 

 spores the following spring. From this source the young fruit, 

 leaves, and twigs become infected early in the season. Later, spores 

 from the spots of apples thus affected may spread the disease farther 

 during the current season. 



Scott and Rorer found almost no spores in mummied fruits of the 

 preceding year and concluded that mummies were not a source of the 

 spring infections. At different times during the spring of 1915 the 

 writer undertook to examine for spores something more than a bushel 

 of mummied fruits that had been badly affected with blotch during 

 the preceding year. The varieties selected were Ben Davis and Mis- 

 souri {Missouri Pippin), both of which are very susceptible to the 

 disease. On the average, six blotched areas on each apple, especially 

 selected for the large number of pycnidia contained in them, Avere 

 examined. The p>eriod during which the mummied fruits were col- 

 lected and examined extended from April 1 to June 1, 1915. The 

 fruits were from trees particularly noted during the preceding year 

 as heavily infected with the disease. It was thought that by examin- 

 ing such specimens at intervals during this period it could be ascer- 

 tained (1) whether sj)ores remained in the pycindia through the 

 winter, (2) whether an ascogenous form was produced during the 

 winter or spring, and (3) whether new pycnidia with spores were 

 produced after the growing season started in the spring. All the 

 material was sectioned on the freezing microtome and examined care- 



