103 



as three centimeters below the point where the outward signs of 

 the disease ceased, indicating that in controlling the trouble it is 

 necessary to cut back a considerable distance from the visibly 

 rotted area. 



Figure i, E, shows a plant twenty-three days after an inocula- 

 tion, not with the stem bacterium, but with the organism isolated 

 from typical bacterial leaf-spots such as illustrated in Figure i, 

 A and B. Of seven such inoculations, four gave positive results 

 and the organism was re-isolated. Whether or not the organism 

 causing stem-rot is identical with the one causing the leaf-spot is 

 a question which must be left for further culture work and ex- 

 perimentation. 



Control of black stem-rots 



General control measures, such as careful watering, mentioned 

 for the bacterial leaf-spot, should be effective also in the case of 

 the stem-rot. Seriously affected plants should be promptly de- 

 stroyed to remove sources of new infection, and the pots in which 

 they were grown should be thoroughly sterilized. In cases of 

 early infections, cutting back as far as possible from the infected 

 area and treatment of the cut surfaces and of the soil with a fun- 

 gicide such as Semesan should save the plants. Cuttings should 

 not be made with an unsterilized knife which has been used in the 

 vicinity of infected plants, and unnecessary wounding and rough 

 handling should be avoided. The remedy suggested for control of 

 the leaf-spot which involves the picking off of infected leaves only 

 increases the probability of infection by the stem bacterium, if the 

 leaf stalk is broken off close to the stem, leaving a fresh scar. 



In case one is having trouble with black rots that attack the 

 lower ends of cuttings (foot-rots) the soil is probably infected 

 with one of the PytJiium damping-off fungi, or with the virulent 

 strains of the stem-rot or leaf-spot bacterium. The soil should be 

 replaced or sterilized. 



B. O. Dodge, 

 Martorie E. Swift. 



