274 



I INGOUS DISEASES OF PLANTS 



the fruit near a decayed area is invariably bitter. This character, 

 which appears to be quite constant, has given the disease its 

 popular name. Affected fruits usually fall from the trees after 

 a spot has attained considerable size. Nevertheless, in excep- 

 tional cases the diseased fruits may hang on, and when the 

 whole fruit has decayed as a direct or indirect effect of the fun- 

 gus, they become dried, and to these fruits the term tf mummy " 

 has also been applied. 



The bitter rot fungus has been found upon various varieties 

 of the apple. In some sections it is reported more commonly 

 upon Ben Davis and Grimes Golden, but this may be more 

 particularly due to the fact that these varieties were more gener- 

 ally grown in the regions for which the report was made. The 

 fungus is, in fact, notably unrestricted as to host. The apple 

 is unquestionably the fruit most injured, yet the same fungus 

 may be parasitic upon the grape, peach, pear, tomato, eggplant, 

 and pepper ; at least, if infection experiments alone can be 

 trusted to indicate what may take place in nature, the hosts 

 above mentioned, as well as others, are all susceptible. 



The fungus. The life history of this fungus includes two 

 stages, one an imperfect fungus, or properly glceosporial stage, 

 which is commonly produced upon the fruit, and the other 

 an ascigerous stage, which may occasionally be produced upon 

 a fruit or twig, and readily developed in artificial cultures. 1 It is 

 believed that the early infection of the fruit frequently arises from 

 the development of pustules bearing conidia in canker areas, the 

 spores falling from the canker areas to the fruit below. It ha^ 

 been frequently observed that affected fruits on a tree may map 

 out a pyramidal area, at the cone of which may be found a 

 cankered limb. Such canker areas (Fig. 123) apparently develop 

 the conidia early in the season. The cankers are in the form 

 of sunken areas upon twigs or limbs, and they are often round 

 or oblong, sometimes several inches long, the bark covering such 

 areas being cracked and broken. The bark readily dries out and 



1 As a result of his studies upon the fungus causing bitter rot Edgerton states : 

 " There are apparently two forms on the apple. These are separated in their geo- 

 graphical distribution apparently by thermal lines ; the southern form differs from 

 the northern considerably in cultural characters and it differs also slightly in the 

 characteristics of the perithecium and the acervulus." 



