298 A Bacterid! DlHeaae of Turnip (Brassica Napus) 



tubes were examined at intervals, some were always found to be more 

 advanced in disease than others. Those which were spongy in appearance 

 were brown or yellowish-brown in colour but the more succulent blocks 

 were always wliitish-f;rey. The difference of coloration in the diseased 

 tissues may therefore be due to oxidation. Further proof of this was 

 established by the appearance of the diseased blocks in the tubes after 

 incubation periods of 24 hours, 48 hours, and 7 days. At first they 

 showed a whitish-grey transparency around the inoculated part; later, 

 they had become almost completely diseased but still whitish-grey, 

 but after 7 days the blocks were considerably changed and distinctly 

 brown in colour. The darkened colour-, however, was only seen in those 

 portions of the blocks exposed to the air in the tubes; the basal portions 

 immersed in a little water were still light in colour. Still further evidence 

 proving the discoloration to be due to oxidation was obtained by the 

 following experiment. Two conical flasks with side tubes, plugged and 

 sterilized in the autoclave were partially filled with sterile blocks about 

 a cubic centimetre in size, and a little sterile water added. Two rubber 

 stoppers which had previously been boiled in mercuric chloride and 

 dipped in sterile water carried a bent tube, reaching to within half-an- 

 inch of the turnip blocks. Into each a small fragment of diseased turnip 

 was inserted, tlie stoppers quickly replaced and sealed with paraffin wax, 

 sterile rubber connections furnished with pinch-cocks were slipped over 

 the side and the bent tubes. The flasks were connected each to three 

 similar flasks containing a mixture of pyrogallic acid and potash. 

 A current of air was then drawn through the series of flasks for 15 

 minutes. The rubber connections of the turnip-flasks were then closed 

 with the pinch-cocks and the flasks detached. From one turnip-flask 

 the pinch-cocks were removed, and the tube-ends closed with sterile 

 cotton-plugs. Both flasks were then incubated at 20° C. for a week. 

 After 24 hours the blocks around the diseased fragment of turnip intro- 

 duced showed the usual whitish-grey transparency. At the end of the 

 week the contents of the cotton- plugged flask had become brown in 

 colour, whereas the blocks in the sealed flask, all diseased, still remained 

 whitish-grey in colour, and showed no sign whatever of browning, nor 

 did they show any change of colour even after several weeks. Inci- 

 dentally the experiment shows the organism to be facultative anaerobic. 

 Further evidence of this property is given below. 



As previously stated the discoloration in the field plants was con- 

 fined to a distinct zone, between the healthy and diseased tissues. It 

 is possible that the disintegration of the tissues following upon disease 



