18 THE BITTER ROT OF APPLES. 



bitter rot or ripe rot of both apples and grapes was in some way con- 

 nected with this fungus. A complete description of the fungus and 

 its various stages is given in a succeeding chapter, and it will be neces- 

 sary at this point to simply mention in brief the general appearance of 

 the fungus in the orchard and the reasons for connecting this fungus 

 with the bitter rot. 



Reference has already been made to the appearance on diseased 

 fruits of more or less regular rings of pustules. In these pustules 

 small one-celled spores are formed, which exude from the pustules 

 after they have broken through the epidermis. In the orchard these 

 spores seem to be produced abundantly only when the air is heavy 

 with moisture. Heavy dews and rain wash away the pink spore 

 masses, leaving the ragged mouths of the pustules freely exposed. The 

 appearance of the pustules and the discharge of the spore masses are 

 the only evidences of fungus activity visible during the attack. 



These pustules and spores are, however, always present in apples 

 affected with the bitter rot, and no cases of this disease are known 

 where these spores have not appeared at one stage or another. More- 

 over, inoculations of sound fruit with the spores of Grlceosporium 

 fructigenum Berk., made by many experimenters, have invariably 

 produced the disease (PI. II). There is, therefore, no doubt whatever 

 that the bitter rot or ripe rot of apples and of some other fruits is 

 caused by the bitter-rot fungus (Glceosporium fructigenum Berk.). 



RATE OF DEVELOPMENT OF THE BITTER ROT. 



The rate with which this disease develops depends largely upon con- 

 ditions of temperature and moisture. During some summers it may 

 take several weeks for the disease to develop to any extent after its 

 first appearance. Then, again, it may start on a fruit during the night 

 and in three to four days entirely destroy it. Apples inoculated 

 with the bitter-rot fungus and kept in incubators at a temperature 

 of 37° C. (98.6° F.) will show spots three-fourths of an inch in diame- 

 ter, with numerous pustules, in forty-eight hours after inoculation. 

 As has been stated above, the disease will develop in several days in 

 epidemic form when heavy dews fall during the night, followed by 

 hot, cloudy days. The condition of the apple fruit at the time of 

 the attack influences to some extent the rate of development. Thus 

 green fruits do not suffer as severely from the disease nor does the 

 disease progress as rapidly as with fruits which are almost ripe. The 

 disease progresses at different rates on different varieties of apples. 

 Some are more easily affected than others. In general, it may be said 

 that hot, muggy weather is most favorable for the rapid development 

 of the bitter rot. 



