BACTERIAL DISEASES OF PLANTS 193 



by fission or by formation of conidia. The organism 

 takes the form of a straight cylindrical rod. 



Qallionella ferruginea (Chlamydothrix ferruginea} assumes 

 the shape of a hairpin, with the prongs twisted round one 

 another. 



Spiropliyllum ferrugineum (Ellis) is a flat, tape-like 

 organism, spirally twisted, which multiplies by conidia 

 formation. 



These higher bacteria have not the power to dehydrate 

 and reduce the ferric hydroxide to bog ore. ' Bacillus 

 M. 7 ' (Mumford) not only precipitates ferric hydroxide 

 from iron solutions, but, by an anaerobic action, also 

 transforms this to bog ore with partial reduction of the 

 iron to a ferrous state. Mumford thinks that to this 

 organism are probably due the deposits of bog ore. ' Bacil- 

 lus M. 7 ' is a motile, sporulating bacillus that occurs 

 singly or in chains of three or four units. 



For further information on the iron and sulphur bacteria, 

 and also for the bacteriology of fermentation processes 

 in the arts, see David Ellis's ' Outlines of Bacteriology.' 



BACTERIAL DISEASES OF PLANTS. 



Black Rot of Cabbage (Pseudomonas or B. campestris) 

 is a disease of the fibro-vascular bundles, which become 

 dark brown or black. On cutting across the petiole of a 

 diseased leaf the affected bundles are seen as dark points, 

 When so many of the bundles are affected as to cut off the 

 supply of water to a leaf, the blade dries up and resembles 

 a piece of brown parchment, the blackened veinlets stand- 

 ing out sharply against the brown background. As the 

 leaves in the head become affected they decay, producing 

 a dark vile-smelling mass. 



Commercial seed is a factor in the distribution of the 

 disease. The organism may gain entrance through 

 broken roots at the time of transplanting, or through the 

 water pores at the margin of the leaves. All cultivated 

 plants of the Crucifer family are liable to be attacked. 

 Slugs and insects may convey the disease. B. campestris 

 is a short, motile, Gram-negative bacillus, which liquefies 

 gelatin, digests casein, and produces a yellow pigment 

 on potato. 



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