Crown-Gall 259 



and increases from year to year until the plantation becomes worth- 

 less. On old plants every bud is sometimes deformed. Unlike most 

 plant diseases this one does not seem to vary in destructiveness in 

 different seasons except as it steadily increases. The affected flower- 

 buds either die or produce only worthless fruit. 



The mycelium of the fungus is found within the diseased leaf -buds 

 and is especially abundant within the flower-buds. Spores are pro- 

 duced within forty-eight hours after the flower-buds open. These 

 spores are carried to the young buds of the current year's growth, 

 germinate and produce mycelium which remains practically dormant 

 within the bud during winter. Canes or parts of canes covered with 

 grass are seldom affected. The mycelium develops rapidly in spring 

 but does not penetrate the tissues of the plant and pass back into 

 the stem, a fortunate fact. 



Treatment. Spraying has not proved effective against this dis- 

 ease. The fact that the spores are produced during the period of 

 bloom and fruit-growth indicates that it will not be a feasible method 

 of control. Since the fungus does not reach beyond the base of the 

 bud it is possible to control it by hand-picking the diseased buds. 

 This should be done as soon as the leaf-buds open. They can then 

 be readily seen, but later are more difficult to find. Experiments in 

 Delaware indicate that this is cheaper than spraying would be if 

 effective. It has not been possible to entirely eradicate the disease, 

 but it has been held in check. The yield has been better, the fruit 

 of better quality and the life of the plantation prolonged from one 

 to two years. Plants for setting should preferably be taken from 

 young plantations, since the disease is less prevalent in new fields. 

 Reference. 



Cook, Del. Expt. Sta. BuU. 93. 



CROWN-GALL 



Bacterium tumefaciens, Smith et al. 



This disease is characterized by a rough knotty growth about the 

 stem of plants at the surface of the ground, on the roots beneath, 

 or on the canes or branches. The knots or galls, in their commonest 

 form, have a rough or granular appearance, somewhat resembling, 

 when young, the callous growth at the end of a cutting. When old 



