194 



BACTERIA IN RELATION TO PLANT DISEASES. 



observed. This has been the general form of the organism seen nearly every summer since 

 1895 in tomato stems and potato stems collected in various southern States, and in cultures 

 made therefrom. In glycocoll solutions Honing has seen involution forms (p. 253). 



This organism is often not so pure a white as Bacillus amylovorus or Bacillus trachei- 

 philus. In the host plant and on certain media it may be described as pure white at first, 

 but soon grayish-white, dirty white, or brownish-white, becoming brown, since it produces 

 a soluble brown pigment which modifies its appearance. On steamed potatoes this stain is 

 usually developed to such an extent that the cultures soon become brown or even nearly 

 black (3 to 10 days) ; the water also is browned around potato cylinders. This pigment, 

 which is produced in the dark as well as in the light and which on potato is not infrequently 

 as black as tar (pi. 23, figs. 8, 10, and pi. 41, fig. 4), is soluble in water and glycerin and 

 slightly in methyl alcohol on long stand- 

 ing; it is insoluble in ethyl alcohol (exp. 

 1896, 1905*), ether, chloroform, xylol, and 

 carbon bisulphide. The browning did not 

 occur in the absence of sugar and alkali. 

 The pigment is not destroyed by weak 

 acids or alkalies. It behaves in some re- 

 spects like a humous compound, i. e., it 

 does not dialize readily and is precipitated 

 by compounds of iron and calcium. 



This organism grows well in pepton- 

 ized beef-bouillon, with or without the 

 addition of sodium carbonate, and yields 

 much more precipitate than similar cul- 

 tures of B. tracheiphihis ; a brown stain 

 appears, and this was especially noticeable 

 in case alkali was added; tendency to 

 form pellicle rather slight. Old peptone- 

 water cultures do not brown. In +15 

 peptonized beef-bouillon the District of 

 Columbia organism at the end of 20 days 

 showed good clouding with an enormous 

 number of small pseudozoogloeae, but with 

 no rim or pellicle ; the dirty white or pale 

 brownish precipitate covered a breadth of 

 13 mm. on the bottom of the test-tube. 

 In Dunham's solution cultures of the Fig 103.f 



same age were well clouded, but less so 

 than the bouillons, with only about half as much of the dirty white precipitate. 



Cultivated in milk there is no precipitation of the casein, but after about 3 to 7 weeks 

 the fluid becomes transparent (fig. no, A). Milk was intensely alkaline to litmus paper as 

 early as the twentieth day. The organism is able to live in milk for at least 48 days. The 

 casein of the transparent milk is thrown down by hydrochloric acid (1896, repeated in 1905), 

 and by strong solutions of sodium chloride or copper sulphate. In litmus milk no acid is 

 developed, but after 2 or 3 days the fluid becomes slightly bluer, and this alkalinity increases 

 gradually from day to day until the milk is an intense deep blue. On the twenty-eighth 



'Bad. solanacearum (District of Columbia strain) in gelatin-stab. On adding water to the alcohol the pigment 

 was slowly soluble. 



fFic. 103. Cross-section of a very small portion of a potato-stem (a detail from fig. 102), showing a single vessel 

 occupied by Bacterium solanacearum, the surrounding tissue being free from the bacteria. The lignified wall of the 

 vessel is indicated by fine dots. Slide 166(2. Zeiss photomicrographic stand, vernier readings 14.7 X2. 8. Plant inocu- 

 lated with pure peptone-water culture made direct from the interior of a diseased egg-plant. 



