APPLE DISEASES 19 



inoculation spots an inch in diameter will develop on the fruits ; 

 however, the rate of rotting depends on the temperature and 

 the age and variety of the fruit concerned. As previously 

 pointed out, the fungus develops fruiting pustules, acervuli, 

 by the time the spot is an inch or less in diameter. Their 

 general appearance and arrangement has also been described. 

 Within the acervuli conidiophores arise, each stalk being capable 

 of developing several conidia successively at the free outer end. 

 These spores, as they are formed, pile up at the apex of the 

 acervulus and in quantities are pink. These groups of conidia 

 in the concentric or scattered acervuli produce a very striking 

 appearance, which forms one of the most characteristic symp- 

 toms of the disease. When moist the conidia cohere in sticky 

 masses for a time, but when wet are easily separated and washed 

 to other points during the rains. Such conidia are in turn 

 capable of inducing bitter-rot and within three to seven days 

 another crop of conidia is ready for dissemination. This 

 process may be frequently repeated from 'June to October, if 

 weather conditions are favorable. Many of the conidia are 

 carried in rain drops by heavy winds to other apple-trees 

 which thus become new centers of infection. Many conidia, 

 too, are deposited on dead parts of a tree and there germinate, 

 and establish the fungus for the winter. Accordingly it has 

 been shown that the pathogene not only hibernates in the 

 bitter-rot mummies and cankers, but also in the Illinois blister- 

 cankers, dead tips of fruit-spurs, frost-injured portions of 

 limbs, fire-blight cankers, blotch .and black-rot cankers. In 

 any or all of these places the fungus overwinters in the form 

 of mycelium. In the spring, the parasite resumes activities 

 by developing acervuli from which the first spring crop of 

 conidia are produced. The fungus has a sexual stage, in 

 which perithecia, asci and ascospores are borne, but it has not 

 been shown that this stage is important in the life-cycle of 

 the organism. 



