CHAKACTER OF THE SPOTS. 



17 



Fig. 2. — Diagram showing how the 

 bitter-rot fungus decays an apple. 



The brown coloration of the spots on the apple fruit is an indication 

 of the decayed condition of the tissues immediately under the spots, 

 in which region the threads of the bitter-rot fungus are bringing about 

 changes in the firm tissue of the fruit which make it appear deca} r ed. 

 The lateral progress of the disease, evidenced by the increasing 

 diameter of the brown area, is accompanied by a corresponding prog- 

 ress of the disease into the fruit (figs. 2 

 and 3). The rotted mass, which is an 

 inch in diameter at the surface, usually 

 extends inward to the core of the fruit. 

 The rotted mass shrinks somewhat in 

 volume, hence the sunken character of the 

 spot outside. There is usually a sharp 

 dividing line between the rotted mass and 

 the sound tissue. In this respect the bit- 

 ter rot differs from the black rot of the 

 apple. 



The size of the diseased areas on the 

 fruit increases rapidly after an infection, and eventually the whole 

 fruit may be affected. Where two or more separate infections 

 take place the diseased masses fuse (PI. I). The separate rings of 

 fruiting bodies join and the two sets of hyphae then grow on just 

 as if there had been but one. The completely rotted fruit appears 

 considerably shrunken, especially if there have been several cen- 

 ters of infection. The fruit hardly ever decays entirely, as do apples 



attacked by the black rot; as a rule there 

 are small patches of healthy cells which 

 hold out a long time. The affected fruit 

 falls from the tree during all stages of 

 the disease. (See PI. III.) In this case, 

 as in other instances of fruit diseases due 

 to fungi, a hastening of the ripening proc- 

 ess takes place. The diseased fruits are 

 heavier than ripe fruits, and are readily 

 shaken from the trees. There are proba- 

 bly other changes taking place in a dis- 

 eased fruit which influence its condition and 

 bring on premature fall, much as with fruits stung by various insects. 



Fig. 3.— A later stage of bitter-rot 

 decay. 



CAUSE OF THE BITTER ROT. 



The bitter rot of apples is due to a fungus, Glososporium fructige- 

 num Berk., which grows in the ripening tissues of the fruit, thereby 

 inducing decay. The earliest accounts of this fungus deal largely with 

 its systematic position, but it was recognized at an early date that the 



26802— No. 44—03 2 



