164 MANUAL OF FRUIT DISEASES 



ment may consist of short, slender twigs. Sometimes one 

 healthy shoot is found among diseased ones. Shoots of brooms 

 will frequently remain green after old canes are dead. When 

 flower-buds open, they display various malformations : some- 

 times the deformity is slight, again extensive, depending some- 

 what on the extent of infection. Blossoms are usually affected, 

 the sepals and petals being thickened. Some growers errone- 

 ously regard these diseased blossoms as male flowers. At 

 times the blossoms are increased in numbers ; this is especially 

 true of the petals. Diseased petals have the . appearance of 

 being doubled, whence the name double-blossom. Other parts 

 of the flower may show abnormal growth, due to the double 

 blossom pathogene. The stamens and ovaries are affected. 

 It happens at times that certain flowers appear healthy, but such 

 flowers may have diseased ovaries. Every bud in an affected 

 plant may be diseased. Sometimes late blossoming is induced 

 in plants attacked by the double-blossom parasite. In such 

 cases the blossoms are smaller than normal. 



Cause. 



The abnormal bud-development just described is due to the 

 fungus Fusarium Rubi. In the early spring its mycelium may 

 be found between the parts of affected buds. With the advent 

 of proper conditions growth is resumed. The mycelium does 

 not pass from the bud into the stem. It does, however, 

 enter certain parts of the bud. The ovaries are penetrated by 

 way of the stigma and the style. An abundant growth of 

 mycelium takes place within these organs, but the carpels and 

 ovules are not penetrated. Neither are the stamens penetrated, 

 although the hyphse may be found abundantly between them. 

 Wherever the mycelium enters the tissues of a bud, haustoria 

 are sent into the cells. Thus the fungus feeds on its host, stimu- 

 lating the leaf-buds to witches'-broom formation, and dwarfing 

 the ovaries of the flowers. This influence is also felt by other 

 parts of the flower, as noted under Symptoms. 



