BLACK ROT OF CRUCIFEROUS PLANTS. 



317 



four or more elements occur. Single elements then generally fall within the following meas- 

 urements: 0.7 to 3.0/x by 0.4 to 0.5^. It is 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 30C. and from old potato cultures at refrigerator 

 temperatures, is shown in figs. 125-127. When treated with flagella-stains the diameter is 

 greater, viz., 0.7 to 0.9/x, 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 ioo/z 

 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 



Fig. 115.* 



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. 



*Fig. 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. 



