2 30 



THE DISEASES OF FRUITS, 



been satisfac- 

 torily held in 

 check by spray- 

 ing with fungi- 

 cides. The or- 

 chardists upon 

 our western coast 

 may well seek 

 the information 

 for them in the 

 partment of Agriculture. 



The Plum. — Black Knot 

 (^Plowrightia morbosa Sacc.) 

 is the most conspicuous 

 fungous enemy of the plum. The 

 attack is made upon the young 

 twigs in the spring, which soon 

 begin to swell, the bark cracks, 

 and upon the surface of the fissure 

 the fungus produces an olive coat- 

 ing of spores by means of which 

 the disease is spread. This is 

 one of the very deeply - seated 

 fungi, its threads being located 

 chiefly in the growing layer be- 

 neath the bark, and ■ when the 

 final spores are produced they are 

 located in sacs embedded in a 

 hard black crust of the distorted 

 branch, from which the common 

 name is naturally derived (see 

 Fig. 288). 



The black-knot fungus attacks 

 a number of kinds of wild plum 

 and cherry trees. It is not infre- 

 quent that the hedge row sur- 

 rounding an afflicted orchard con- 

 tains many wild shrubs and trees 

 conspicuous, especially during the 

 winter, for the many black excrescences upon their branches, 



Fig. 288.— a portka ot' a Fmm 

 Branch with the Black Knot in 

 mature form. (From Farlow. ) 



