512 DISEASES OF CULTIVATED PLANTS 



Black rot of horse-radish. During the past season an 

 extensive outbreak of black rot, caused by Pseudomonas 

 campestris (Smith), has been recorded as attacking horse- 

 radish. The symptoms are identical with those described 

 under black rot of cabbage. It is highly probable that all 

 plants belonging to the order Cruciferae are susceptible to this 

 disease. 



Maize disease. Prof. E. F. Smith has now proved that 

 Pseudomonas Stewarti is the cause of the sweet corn disease 

 of Long Island. The organism is rod-shaped, with a polar 

 cilium, i-2Xo'5-o'9 /x, and occurs in the vascular bundles. 

 It is yellow, aerobic, but capable of becoming anaerobic. 



Smith, E. F., Proc. Amer. Assoc. Set'., 47, p. 422 (1898). 

 Smith, E. F., Proc. Amer. Assoc. Set., N. S., 17, p. 458 



(1903)- 



Bacterial disease of lilac. A disease of lilac, not at all 

 uncommon in this country, has been shown by Dr. Klebahn 

 to be due to bacteria. In May or the beginning of June, 

 when the young shoots are yet soft and tender, the internodes 

 and young leaves often show large, blackish blotches, due to 

 the presence of bacteria, which occupy the intercellular 

 spaces. The organism is called Pstudomonas syringae (Hall). 



Klebahn, II., Krankheiten des Fliedcrs, p. 5 (1905). 



Black dry rot in swedes. Professor Potter describes a dry 

 n>t of swedes, caused by a bacterium belonging to the genus 

 Pseudomonas. Externally the plants show but little evidence 

 of disease ; however, when the root is cut open, the centre is 

 seen to consist of a blackish mass of disorganised tissue-, in 

 which are numerous cracks and cavities. In a more advanced 

 stage of disease the root becomes hollow, the rind alone 

 remaining as a mere shell. During decay the bulb remains 

 fairly dry. 



' The special bacterium causing this rot in the swede is a 

 short, motile rod 3 /< X 1 /'. It is an aerobic form, liqui- 

 fying 5 per cent, gelatine. Great difficulty has been found 

 in staining the flagella, but by using the well-known methods 

 of Van Ermengen and of Lowitt I have been able to deter- 

 mine the presence of a single polar flagellum, and, hence, 

 adopting Migula's classification, it must be placed in his 

 genus Pseudomonas. 



Potter, Jo urn. />'</. A^ric, 9, p. 28 (1902). 



