APPLE BLOTCH AND ITS CONTROL. 5 



fully under the microscope. In the old pycnidia no spores were 

 found. No ascogenous stage and no newly formed pycnidia were 

 discovered. The fungus appears to be in no way saprophytic, since 

 not only does it fail to live over on decayed fruits, but it dies out in 

 the older parts of the twig cankers, living only along the margins 

 and dying out entirely in the third or fourth year as the twig be- 

 comes more woody. 



In order to confirm the cross- inoculation experiments of Scott 

 and Rorer, in which the disease was produced on the fruit by spores 

 from twig lesions and on the twigs by spores from diseased fruits, 

 the writer undertook a series of experiments differing from those of 

 Scott and Rorer in that the latter used spores taken directly from 

 twig lesions and diseased fruits, whereas those of the writer were 

 made with spores from pure cultures from those sources. The fungus 

 isolated from twigs and fruits from Kansas was grown on sterile 

 apple twigs in pure culture, and when the spores were mature a 

 suspension of them in sterile water was sprayed on leaves, fruit, 

 and twigs. Inoculations were made on twigs, water sprouts, and 

 fruits of the Missouri variety on July 6. On August 7 typical blotch 

 spots began to appear on the leaf blades and petioles, with an abun- 

 dance of fertile pycnidia in the dark sunken lesions on the petioles 

 and midribs (PI. II, fig. 5). Minute spots on the fruits also were 

 beginning to appear. On September 6 the spots on leaves and 

 fruits were numerous and conspicuous. The disease was beginning 

 to appear also on the twigs and water sprouts. By September 14 

 lesions on the stem portion of the water sprouts and twigs were 

 appearing abundantly. These were black raised areas, bearing 

 numerous pycnidia filled with spores, and were only on the younger 

 portions of the twigs and water sprouts. The fungus was reisolated 

 from leaves, fruit, and twigs and reidentified as Phyllosticta 

 solitaria. 



The writer at various times has attempted to infect the fruit in 

 August and September with spores from pure cultures, but without 

 success. Apparently fruit and twigs become resistant as they grow 

 older, possibly through the increasing impermeability of the epider- 

 mis and the changing of stomata to lenticels. The heaviest infections 

 on fruit occur early in the season, decreasing as the season advances. 

 This is due, not only to a decrease in the number of spores produced 

 by the fungus in the cankers and fruit, but probably in a much 

 greater degree to the previously mentioned increased resistance on 

 the part of the fruit. The writer has never been able to inoculate 

 fruits of Ben Davis and Missouri after August 1 by spraying them 

 with a suspension of spores in distilled water. It may be noted also 

 that at that time the natural supply of spores capable of infecting 

 is still not wholly wanting in so far as those produced from cankers 



