100 



THE PLUM. 



Diseases of the Plum. PLUM POCKETS. This is a name 

 given to certain peculiar bellow deformities which occasionally 

 take the place of the plums (see Pig. 74). They consist merely of 

 a thin shell with no evi- 

 dence whatever of seed. 

 Some seasons this dis- 

 ease is very abundant, 

 and then for a number 

 of years it may scarce 

 appear at all. It is due 

 to the presence of a 

 parasitic fungus (Taph- 

 rina pruni) which at- 

 tacks the young fruit, 

 and by growing within 

 it causes the peculiar 

 development which fin- 

 ally results in the for- 

 mation of the so-called 

 pocket. The only 

 course of treatment 

 which can be recom- 

 mended is that of re- 

 moving and destroying 

 the pockets before they 

 reach maturity. It will 

 sometimes be found 

 that a single tree will 

 be troubled with this 

 fungus for a series of 

 years, and it will not 

 spread much. When 

 this is the case such 

 trees should be des- 



FiG. 74. Plum pockets, or diseased plums. 



troyed, as they are 

 likely to be centers of 

 infection. Some varieties are more subject to its attack than others. 

 BLACK-KNOT, OR WART OF THS PLUM, is the common name of 

 the fungus disease of this tree which manifests itself by knot-like 

 or wart-like growths appearing on the smaller limbs as well as on 

 the larger branches, and sometimes even on the trunk (see Fig. 75). 

 In sections of the country where Prunus domestica is grown this is 

 one of the most serious obstacles to successful cultivation of the 

 plum. Our native plums are not often destroyed by it, but it 

 sometimes causes serious injury to them. This knot-like growth is 

 spongy and of a black color. Upon examining it with a microscope 

 it is found that the surface has many little cavities which contain 

 the spores by which the disease spreads. It is probable that the 



