BACTERIA OF PLANT DISEASES. 575 



finally to disappear. The cavities contain innumerable bacteria mingled 

 with fragments of the dissolved bundles and of the surrounding parenchyma. 

 "First described by Dr. J. H. Wakker from the Netherlands, where it 

 often causes serious losses in the hyacinth gardens. Not known to occur in 

 any other part of the world " (E. F. Smith). 



BACILLUS CAMPESTRIS (Pammel) . 



The cause of brown rot in Cruciferous plants. 



" Pseudomonas campestris (Pammel). Yellow, rod-shaped, motile 

 micro-organism. Size and color varying according to substratum, food 

 supply, etc. Generally 0.7 to 3.0 by 0.4 to 0.5 ,. Coior dull wax yellow or 

 canary yellow. Occasionally as bright as light cadmium or as pale as prim- 

 rose yellow (Ridgway's color scale). One polar flagellum. Non-sporiferous, 

 so far as known. Pathogenic for various Cruciferous plants, entering and 

 dwarfing or destroying the host plant through the vascular system, which 

 becomes decidedly brown. Aerobic but, so far as known, not a gas or acid 

 producer, i.e., not facultative anaerobic. Forms cavities around the bundles 

 but seems to be only feebly destructive to cellulose. Produces a brown pig- 

 ment in the host plant and on steamed Cruciferous substrata, especially the 

 turnip. Grows very rapidly on steamed potato cylinders at room tempera- 

 tures, but without odor or the formation of any brown pigment. Liquefies 

 gelatin. Grows feebly at 7 C., better at 10 a C., but still feebly ; grows well 

 at 17 to 19 C. ; grows luxuriantly at 21 C to 26' C. ; grows very feebly at 37 D 

 to 38 C. ; will not grow at 40 C. ; and is killed by ten minutes' exposure to 

 51 C. Organism closely related to Wakker's Bacterium hyacinthi, from 

 which it differs, so far as I have been able to observe, chiefly in its patho- 

 genic properties, its duller yellow color and its higher thermal death point'* 

 (E. F. Smith). 



PSEUDOMONAS STEWARTI (Smith). 



"A medium-sized rod rounded at the end and motile by means of one 

 polar flagellum, size 0.5 to 0.9 by 1 to 2 //, no spores observed ; found in enor- 

 mous numbers in the vascular bundles of corn (Zea mays) associated with a 

 destructive disease of which it is probably the cause ; color in the host plant 

 and in culture media yellow (buff to chrome or ochre, occasionally a pale, 

 dirty yellow) ; aerobic and facultative anaerobic ; grows in all ordinary cul- 

 ture media ; bears alkali well (soda) and plant acids extremely well ; grows 

 luxuriantly in Uschinsky's solution ; growth enormously stimulated by cane 

 sugar, grape sugar, and galactose ; growth not favored by five-per-cent doses 

 of lactose, maltose, dextrin, mannite, or glycerin in nutrient starch jelly ; 

 diastatic action feeble, i.e., able to obtain food from starch only with much 

 difficulty ; produces alkalies in all sorts of media and acids in the "presence of 

 grape and cane sugar; reduces litmus slowly; does not liquefy gelatin 

 (Stewart) ; does not liquefy Loftier 1 s blood serum ; grows well at summer 

 temperatures of 25 to 30 C. ; does not die out quickly in culture media ; does 

 not produce gas; sensitive to light (Stewart); occurs in New York and 

 Michigan and maybe looked for in all parts of the United States" (E. F. 

 Smith). 



BACILLUS AMYLOVORUS (Burrill). 



Described by Burrill (1880) as the cause of pear blight. Etiologi- 

 cal relation to this disease confirmed by Arthur (1884 to 1887) and 

 by Waite (1891 to 1895). 



' ' Beginning in the spring the germs on the new growth of the season first 

 appear on the negative discs of the blossoms. The bacilli live and multiply 

 in the nectar and are able to enter the nectar glands without a puncture or 



