BROWN ROT OF SOLANACEAE. 



193 



THE PARASITE. 



Bacterium solanacearum EFS.* is a medium-sized rod with rounded ends. It multi- 

 plies by fission. It often occurs in pairs with a plain constriction (fig. 109). It is usually 

 1.5 to 3 times as long as broad. When crowded in the plant it may be so short as to some- 

 what resemble a micrococcus. It stains readily. When taken from young cultures in pep- 

 tonized beef-bouillon and stained with methyl violet many of the rods are 1.5/u by 0.5/x. 

 Longer and shorter rods occur and thicker and thinner ones, the measurements depending to 

 a considerable extent upon the age of the culture and the kind of stain employed (fig. 109). 

 It is motile at times both in the plant and in cultures, and is often very actively so 

 in young cultures. 

 Owing to imperfect 

 preparations it was 

 at first supposed that 

 the flagella were per- 

 ipheral, but further 

 studiesof these slides 

 and of others subse- 

 quently prepared 

 indicate that the or- 

 ganism is usually 

 motile by means of 

 a single polar flagel- 

 lum, which is much 

 longer than the rod 

 (fig. 109). Pseudo- 

 zoogloeae are com- 

 mon in fluid cultures 

 and inclined to ac- 

 cumulate in the 

 upper layers. Spores 

 have not been ob- 

 served. Longchains 

 and filaments have 

 not been observed. 

 On August 8, 1904, 

 two 3-mm. loops of 

 the District of 



Columbia organism taken from a slant potato-agar culture 3 days old (tube 2, Aug. 5) were 

 put into 15 c.c. of sterile water, and then the faintly clouded fluid was studied in a hanging 

 drop under high powers of the microscope. The organism was actively motile. It was a 

 short rod, single or in pairs, rarely in fours, the doublets with a plain constriction in the 

 middle. The length of each element of the doublet was not more than 1.5 to 1.8 times its 

 breadth. In old potato cultures examined in 1904, the organism was a short rod with 

 rounded ends, single or in pairs, with a plain constriction. Involution forms were not 



*Syn. Bacillus solanacearum EFS.; Pseudomonas solanacearum EFS. 



fFiG. 102. Cross-section of stem of potato (No. 5, 1S96) inoculated with Bad. solanacearum June 1 ; fixed in alco- 

 hol June 11, after being badly wilted for 3 days. The culture used was a tube of peptone-water inoculated directly 

 from the interior of an egg-plant stem. The heavily shaded parts are the ones occupied by the bacteria. There are 16 

 crystal-cells marked by arrow heads (use lens). The parts of the stem not heavily shaded are free from the bacteria. 

 viz, all the bark, most of the pith, and considerable portions of the woody ring. Slide 166(2. Figure somew-hat 

 diagrammatic, especially in the collenchyma and phloem. Compare with fig. 1, vol. II, which shows cross-section of 

 a potato stem in a later stage of the disease. The vessel at X is shown highly magnified in fig. 103. 



1 in m 



Fig. 102. f 



