376 MANUAL OF FRUIT DISEASES 



and to a superabundance of moisture in the atmosphere at the 

 time the fruit was forming. The real cause of plum-pockets was 

 discovered in 1861. 



The parasite spends the winter as mycelium in the smaller 

 branches, as evidenced by the fact that it is found there before 

 diseased fruit appears. Moreover, the annual recurrence of the 

 disease strengthens this opinion. From the affected branches 

 the mycelium grows out into the young ovaries of the fruit, 

 stimulating them to form a remarkable hypertrophy. After 

 the mycelium develops to a considerable degree internally, the 

 threads pass towards the surface. Some of the hyphee push up 

 between the epidermal cells and spread out between these and 

 the cuticle. Here they form a net-work of short cells, which 

 soon grow erect on the surface of the fruit and become asci 

 with ascospores. The ascospores are discharged through the 

 apex of the ascus, but their further history is unknown. Condi- 

 tions favorable to plum-pockets are similar to those favoring 

 peach leaf-curl, namely cool, wet weather in the early season of 

 the year. 



Control. 



Satisfactory control measures have not been established for 

 all sections of the country. It is advised that severe pruning 

 to remove diseased twigs be practiced. It has been found in 

 Montana that trees sprayed with lime-sulfur showed very few 

 diseased plums, whereas more than half of the fruit on un- 

 sprayed trees was destroyed. These results were obtained in 

 1915 by making two applications as follows : (1) just before 

 the flower-buds open, and (2) just after the petals fall. This 

 treatment is advised for other regions where the disease is 

 troublesome. 



REFERENCES 



Galloway, B. T. Plum pockets. U. S. Agr. Comm. Kept. 1888 : 366- 



369. 1889. 

 Hesler, Lex R. Diseases of the plum. Plum pockets. In The Fruit 



