PLUM DISEASES 



375 



less curved (Fig. 109). When young they are smooth, and can 

 be distinguished from the healthy fruit by their pale-yellow or 

 reddish color. Later, the surface is gray and is wrinkled con- 

 siderably. Finally, diseased fruits turn dark-brown or black, 

 and rattle like bladders when brought in contact with any hard 

 substance ; whence the name plum-bladders. In this condition 

 they hang to the tree 

 two or three days, then 

 fall to the ground. 



The younger 

 branches and leaves 

 are affected, which in- 

 creases the damage 

 done to the tree. The 

 growing limbs and leaf- 

 lets become distorted 

 and swollen. In June 

 the diseased branches 

 turn gray, the tissues 

 soften, dry up and die. 

 Shoots arising the next 

 year just below these 

 dead extremities are 

 most frequently af- 

 fected by the disease. 



As the new leaves unfold they turn red or yellow, when affected 

 by the disease, and show an arching of the leaf-blade. In 

 general a curl disease, similar to peach leaf-curl, is developed. 



Cause. 



The cause of these interesting malformations is the fungus 

 Exoascus Pruni. Its growth in the plum-tissues causes their 

 peculiar development, which finally result in the so-called pockets. 

 For a long time the cause of the disease was not known, but was 

 attributed to the work of some insect, to improper fertilization, 



FIG. 109. Plum-pockets. 



