622 MICROBIAL DISEASES OF PLANTS 



on potato; surface film on bouillon; liquefies gelatin rapidly; coagulates milk; 

 ferments glucose with production of H and CO2 in the ratio 1:3; indol positive after 

 forty days; methylene blue reduced; ammonia and HjS produced from bouillon; 

 enzymes: amylase, oxidase, peroxidase; facultative anaerobe. 



Pathogenesis. — Pathogenic to orchids grown in the hothouse and 

 also in their habitat. 



Method or Intection.^ — ^The germs enter the leaf tissue chiefly 

 through wounds caused by careless washing. 



Control. — Use only a soft sponge soaked in a i : 1000 solution of 

 mercuric chloride for wiping the leaves, and avoid excessive watering 

 as this favors the disease. 



Rot of Cauliflower and Allied Plants 

 Bacillus oleracecB — ^Harrison 



History and Symptoms. — -This rot of cauliflower and allied plants 

 was first reported iii igoi from truck gardens in the vicinity of Guelph, 

 Ontario. It is characterized by a soft rot of the roots and a blackening 

 of the stems and leaves. Harrison* has found this condition to be 

 traceable to an actively motile bacillus which invades the intercellular 

 spaces of the plant and destroys the middle lamellae. 



Causal Organism. — Bacillus okraceeB-Hamson is a rod with rounded ends; 

 occurs single or in short chains; measures 2 X 0.6/i; motile "by means of 7 to 13 

 peritrichiate flagella; stains with the ordinary aniline dyes; Gram-negative; in 

 broth heavy turbidity and sediment, no pellicle; stratiform liquefaction of gelatin; 

 on agar spreading, thin, whitish, moist, slightly opalescent; neutral red agar no 

 change in color; litmus milk coagulated, soft curd slowly peptonized; blood serum 

 slightly liquefied; growth positive in Uschinsky's and Fermi's solutions; potato waxy, 

 straw-colored to moist, shining; opt. temp. 30°, max. 42°, min. s°; thermal death- 

 point ss°; facultative anaerobe; slight reduction of nitrates; indol slight; H2S 

 positive; slight gas from glucose and lactose, none from saccharose; acid from 

 sugars; enzymes: proteolytic, diastase, cytase (pectinase). 



Method or Infection. — Infection takes place chiefly through 

 wounds due either to mechanical or insect injuries. Warm weather 

 combined with excessive moisture appears to favor the spread of the 

 disease. 



* Harrison, F. C, "A Bacterial Disease of Cauliflower (Brassica oleracea) and Allied Plants," 

 Cent. f. Bakt., Abt. II, Bd. I3, pp. 46. i8S. 1904. 



