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 (Pl. 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 
