620 MICROBIAL DISEASES OF PLANTS 



into the base of the stem causing it to turn black and rot. The vines 

 grow spindling, turn yellow and die prematurely. The diseased tubers 

 may rot in the soil or later when in storage cause a soft rot of the crop. 



Causal Organism. — Erwin Smith describes the causal organism as a non- 

 spore forming bacillus, motile by means of peritrichiate flagella. It stains with the 

 ordinary stains, but is Gram-negative. The growth is grayish-white on agar and 

 on gelatin plates large, round, white colonies develop promptly. Gelatin is liquefied 

 with funnel-shaped liquefaction. On cooked potato, white to yellowish growth. 

 Raw potato, white growth and black stain. There is a slow acid coagulation of 

 milk with precipitation of casein and reduction of litmus. Thick pellicle and 

 heavy precipitate in potato juice. No growth in Cohn's solution. Moderate 

 production of hydrogen sulphide. Nitrates reduced. No indol. Acid from 

 dextrose, saccharose, lactose, maltose and galactose. Some gas from inosite, 

 lactose and mannite. Facultative anaerobe. Optimum temperature, 28° to 30°. 

 Thermal death-point, 47°- 



Closely related organisms are B. solanisaprus Harrison, and B. atro- 

 septicus van Hall. 



Control. — In view of the fact that the germs are introduced with 

 the seed potatoes, thorough disinfection of the seed with formalin is 

 recommended. 



Bud-rot of the Cocoanxjt 

 Bacillus coli (Escherick) Migula 



History and Distribution. — ^The bud-rot of the cocoanut has 

 been known for more than thirty years in Cuba and is to be found dis- 

 tributed more or less generally throughout tropical America and the 

 eastern tropics. 



Symptoms. — ^Johnston* states that in the acute stages of the disease, 

 the bud, or the growing point in the center of the crown, is affected by 

 a vile-smelliiig soft rot which destroys all the younger tissues. Most 

 of the nuts fall, the lower leaves turn yellow and the middle folded and 

 undeveloped leaves die and hang down between the still green sur- 

 rounding ones. The rot gradually spreads from the base of one spike to 

 another until all are involved and shed their nuts; the leaf stalks become 

 so rotten at their bases that they are no longer able to maintain their 

 natural position and droop or else fall o£f. From a central diseased bud, 

 the infection may spread downward and into the trimk of the tree for 



• Johnston, John R., "The History and Cause of Cocoanut Bud -rot," Bull. 228, Bur, Plant 

 Isd., U. S. Dept. Agr., igi2. 



