BLACK ROT OF CRUCIFEROUS PLANTS. 317 
four or more elements occur. Single elements then generally fall within the following meas- 
urements: 0.7 to 3.0u by 0.4 too.5u. Itis often somewhat irregular in shape, viz., slightly 
crooked or larger at one end than at the other (figs. 123, 124). The appearance of the 
organism from a young bouillon culture at 30°C. and from old potato cultures at refrigerator 
temperatures, is shown in figs. 125-127. When treated with flagella-stains the diameter is 
greater, v7z., 0.7 to 0.gu, or thereabouts. It has no distinct capsule (Harding). In sugar-rich 
media the organism, like other species of this genus, frequently grows out into long chains or 
into filaments in which no septa can be detected (Vol. I, fig. 19). These may be 50 to 1oou 
long. Brenner figures a very short form which he designates as “the normal form on old 
agar cultures,’ and chains from a ‘‘very old exhausted culture.’’ He also states that he 
sometimes found in the plant, in parts long diseased, rods, much longer than the ordinary 
short form. Hecke figures the organism as a short rod; Harding, as a short rod and as 
chains composed of a half dozen easily distinguishable segments. Harding says the cells 
are usually isolated, but during rapid growth short chains consisting of 2 to 8 segments are 
formed. Under exceptional circumstances, not well understood, Harding observed long 
filaments during the first 24 hours of growth. Pammel figures it as a rod 2 to 4 times as 
long as broad, occuring singly, or in pairs or three’s joined at the ends and with a plain con- 
striction. In old exhausted cultures Brenner observed rods with polar bodies. Harding 
frequently obtained a dense polar stain and feeble central stain when he used Ziehl’s carbol- 
fuchsin. The writer has also seen this. Pseudozoogloeae occur frequently in various 
culture-media. No spores have been observed, but under certain conditions the organism 
is very resistant to drying. The flagellum is several times the length of the body and arises 
at or near the end. The writer has not observed more than one flagellum on a pole. The 
motions of the organism consist of tumbling, sinuous, and darting movements. 
*Fic. 115.—Cross-section of a turnip-root (plant No. 53), showing commencement of a cavity due to Bacterium 
campestre. Nuclei are visible in several cells. Cellulose walls clear; lignified walls (vessels) dotted. Drawn from a 
photomicrograph. x 500. 
