SOURCES or APPLE BITTEE-EOT INFECTIONS. 3 



to it in an unpublished manuscript by Coxe, dated iNIay 30, 1829. In 

 this manuscript, apple bitter-rot is referred to as being a common dis- 

 ease, and slaked lime placed about the tree is mentioned as having 

 been advised as a remedial measure. 



The fungus which causes bitter-rot of the fruit also causes a canker 

 of apple branches. As the branch cankers are chiefly important as 

 sources of rot infection, they will be described and discussed under 

 the head " Sources of infection." 



The time of appearance of the rot depends upon weather condi- 

 tions primarily, although it also depends to some extent upon the 

 condition of the fruit and the proximity and number of sources of 

 infection. The fruits of susceptible varieties may be infected even 

 when they are quite young and green, provided the weather is hot 

 and moist and sources of infection are present. On the other hand, 

 some varieties are not easily infected until midseason except under 

 extremely favorable conditions. 



Where the sources of infection are particularly abundant, the dis- 

 ease may gain some headway even during seasons in which the 

 weather is relatively unfavorable for its development. 



Glomerella cingulata (Stoneman) Spaulding and Von Schrenk, a 

 fungus having an ascogenous, or " perfect," form and a conidial, or 

 " imperfect," form, is the casual organism involved in the production 

 of apple bitter-rot. The most common fruiting stage is the 

 Gloeosporium, or conidial, the so-called " imperfect," stage. 



The conidial masses, or acervuli (PI. I, figs. 4, 5, and 6), when 

 newly formed are pink and mucilaginous or thinly gelatinous. 

 Later, however, upon drying they become dark colored and of a 

 hard, horny consistency. It is through the agency of the conidia 

 that nearly all of the damage to the fruit of the apple is brought 

 about. The gelatinous nature of the conidial masses when wet and 

 their horny consistency when dry prevent the dissemination of the 

 conidia by the wind, but raindrops can spatter them about and espe- 

 cially upon the apples located below infected fruit. Excessive mois- 

 ture can also cause the conidial masses to trickle or drip down, and 

 here the wind may play a part in modifying the direction of their 

 downward course. 



Birds probably play some part in the dissemination of conidia, 

 but a much more important part is played by insects, more espe- 

 cially by flies. Clinton (6) in 1902 first showed that the disease 

 could be disseminated by flies. The writer has often observed flies 

 which, after alighting upon infected fruits and coming in contact 

 with the mucilaginous spore masses, have flown and alighted upon 

 sound apples upon the same and other trees. 



As noted by Burrill and Blair (4) in 1902, conidia embedded in the 

 hornv mass of the acervulus, if kept dry, retain their vitality during 



