6l8 MICROBIAL DISEASES OF PLANTS 



3.0M by 0.4M to o.Sn; motfle when young by one polar flagellum; no capsule dem- 

 onstrated and no spores observed; zoogloese in liquid cultures. Stains readily with 

 aqueous stains. Gram-negative. 



It grows readily in the ordinary culture media. Upon potato, growth is charac- 

 teristic; at first light yellow, and in old cultures a golden brown, abundant, moist, 

 shining, slimy. Gelatin liquefied slowly. Litmus milk becomes slightly alkaline, 

 casein separated and gradually redissolved. On nutrient agar, translucent, yellow 

 slime. No gas from dextrose, lactose, etc. ITschinsky's solution, growth retarded 

 and feeble. Aerobic. Indol produced. Nitrates not reduced. Diastase produced. 

 Optimum temperature, 25° to 30°; thermal death-point, Si-S". 



Control.— The removal of diseased leaves in the early stages has 

 been practised by some growers with success, but care must be taken 

 not to remove so many that growth will be checked. Manure con- 

 taining diseased cabbage refuse must not be used. Seed disinfection 

 with 1 : 1,000 mercuric chloride, fifteen minutes, or formalin i :2oo, 

 twenty minutes, is recommended. Rotation of crops, and planting on 

 new land should be practised whenever possible. If practicable, the 

 seed bed should be made in sterilized soil, so that the plants will be 

 healthy when set in the field. 



Wakker's Hyacinth Disease 



Pseudomonas hyacinthi — Wakker 



History. — One of the earliest landmarks in the study, of bacterial 

 diseases of plants is the excellent contribution of Dr. J. H. Wakker,*, a 

 Dutch botanist, who between 1883 and 1888 published five papers on a 

 disease of the hyacinth, caused by Ps. hyacinthi. Erwin F. Smithf has 

 carried the investigation farther and has described the causal organism 

 more fully. The disease was first observed in the Netherlands where it 

 frequently causes serious losses in the hyacinth gardens. It is not 

 known to occur in any other part of the world. 



Symptoms. — The disease is characterized by a yellow striping of 

 the green leaves and the bright yellow sUme produced in the vascular 

 bundles of the bulb. The infection in the leaf spreads slowly to the 

 bulb by the multiplication of bacteria in the vascular system, filling the 



* Wakker, Bot. Centralbl., 1883, 14, p. 31s; Archives neerlandaisos des sci. ex. et naturelles, 

 Tome XXIII, pp. i8-ao. 



t Smith, Erwin P., "Wakker's Hyacinth Germ," Bull. No. 26, U. S. Dept. Agr., Div. Veg. 

 Phys. and Path., 1901. 



