APPLE BLOTCH AND ITS CONTROL. 



6.5 [x. When newly formed it is easy to demonstrate the presence of a 

 gelatinous covering about the spore, especially when, as is often the 

 case, it is prolonged into a stout hyaline appendage (fig. 2). The 

 spores (fig. 3) germinate in 15 to 20 hours. The germ tube is some- 

 what darker than the spore and 

 usually shows a pronounced 

 thickening at the point of emer- 

 gence (fig. 3). More than one 

 germ tube may issue from a single 

 spore (fig. 3). 



Spores from the twig cankers 

 in which the fungus has passed 

 the winter are usually mature and 

 ready to infect the young fruit 

 and leaves about three weeks after 

 the petals have fallen. This was 

 first determined by Scott and 

 Rorer by noting the latest time 

 at which spraying would effectively 'prevent infection. The time of 

 infection was directly determined by the writer during the seasons 

 of 1914 and 1915 by germination tests of spores from twig cankers. 

 Table I shows the results of such tests. 



Fig. 3. — Germinating spores of Phyllo- 

 Sticta solitaria. Spores from Ben Davis 

 twig cankers. May 25, 1914. 



Table I. — Results of germination tests of spores of apple blotch from twig 



cankers. 



Date. 



Germi- 

 nating 

 sjpores. 



Date. 



Germi- 

 nating 

 spores. 



Date. 



Germi- 

 nating 

 spores. 



1914. 

 Apr.30 



Per cent. 

 

 

 

 

 2 



1914. 



Per cent. 

 

 

 75 

 75 

 75 



1915. 

 May 13 



Per cent. 

 10 





May 21... 



May 17 



20 



May 6 



May 23 



May 21 



20 



May 8 





May 24 



75 



May 9 



May 29 



May28 



75 











For each test, pyenidia were scraped from the newer portions (the 

 current year's growth) of young twig cankers. These pyenidia were 

 then examined under the microscope for spores. If spores were suffi- 

 ciently abundant and appeared to be mature, they were suspended in 

 distilled water in Van Tieghem cells and the percentage of germinat- 

 ing spores was noted daily for periods ranging from three to five 

 days. As the spores when mature usually germinate within 24 hours, 

 it was really unnecessary to prolong the attempted germination over 

 so long a period. The cankered twigs used in this work in 1915 were 

 collected from the same trees as those used in 1914. 



During both seasons the time of petal fall was April 28. As these 

 two seasons were about average ones, it is evident that in the Ozarks 



