222 BACTERIA IN RELATION TO PLANT DISEASES. 



rich in humus it is seldom seen. Only exceptionally does the disease begin in the seed-beds, 

 and it is not generally observed until some weeks after setting out the tobacco. If the 

 weather is dry the first conspicuous signs are flagging of the leaves. In such plants the 

 base of the stem is diseased and the tap-root, if not other roots. Where a whole field 

 shows this disease it may be assumed to have been very badly planted, i. e., hastily or 

 with too old plants. Rains favor the spread of the disease, and topping, removal of leaves, 

 suckers, etc., should be done, as far as possible, in dry, sunny weather. 



Up to the time of publication of his paper Dr. van Breda de Haan had secured very 

 few, if any, pure-culture infections. He had reproduced the disease in the field by direct 

 infection, using slime which had just extruded from the vascular system of cut stems, 

 obtaining an abundance of the bacteria, with typical signs of the disease in the pith 26 cm. 

 above the wound. Later, at Buitenzorg, he states that he reproduced the disease by inject- 

 ing a pure culture in bouillon, but surely not with the coccus form 8^ in diameter. His 

 field observations seem to have been numerous, but the laboratory work appears to have 

 been meager. 



In 1901, in a general paper on tobacco diseases, Dr. Hunger devoted a chapter to this 

 same disease, confirming van Breda de Haan's statements respecting its prevalence in Deli, 

 the signs of the disease, and the great frequency of underground infections through injuries 

 due to eel-worms and other causes. He was not able to confirm de Haan's statement that 

 the disease is due to a Micrococcus.* Dr. Hunger found this disease due to a much smaller 

 rod-shaped micro-organism which he identified as Bacillus solanacearum. He states that 

 he obtained infections with this organism on tobacco and that he could not distinguish it 

 from the organism attacking tomatoes in Java, nor the latter from that described by Smith 

 from potatoes, tomatoes, and egg-plants in the United States. 



The following statements respecting the Sumatran tobacco disease are translated and 

 condensed from Hunger's Dutch paper: 



This slime-disease was so named by van Breda de Haan, who first investigated it. It is caused 

 by a bacterium which lives as well in the above-ground as in the under-ground plant, but which was 

 not exactly recognized by the discoverer, as may be seen from his description on page 17 (544). 



From van Breda de Haan (whose communication is here borrowed in part with certain correc- 

 tions) the bacteria received no name. 



As the result of an earlier investigation [tomato disease] I came to the conclusion that the slime- 

 disease of tobacco was caused by Bacillus solanacearum Smith, to which same conclusion Raciborski 

 likewise arrived. 



The disease occurs over all Deli, as well in the seed-beds as in young and old tobacco, chiefly in 

 the latter, because it occurs most seriously during the period of heavy rains. 



In the attacked seedlings the lower part of the little stem is dark colored and very flabby, so that 

 it often falls over, while the small leaves wilt and in part hang down brown. 



In large tobacco this disease begins commonly to be noticeable first in dry weather through the 

 interruption of the water-movement in the above-ground parts of the plant. This is shown by the 

 wilting of the leaves. At the same time they lose their fresh green color and there appear upon the 

 ears of the leaf pale green spots, and afterwards also upon the blades themselves, and these speedily 

 become brown and dry out. 



The harvested tobacco from such slime-diseased plants is often unripe. 



The lower end of the stem gets then a dark color and perishes within, so that it can be easily 

 squeezed together between the fingers. The lower leaves become quickly yellow and die before 

 ripening. 



The root-system of the attacked plant is colored brown, the main root is mostly black and rotted 

 at the top. Sometimes also the white, sound, side roots found on healthy plants are here wanting. 



From the root-system the decay continues slowly upward, by means of which the pith of the 

 stem is finally wholly decayed into a slimy mass, wherefrom the name of this disease (slime-sickness) 

 was taken. The disease does not remain limited to the stem, but continues in the leaf-stalks and 

 infects in this way also the leaves, causing spots to appear upon the leaf-surface. 



Hunger noted the occasional presence of a round yeast 0.008 mm. in diameter in his tomato tissues diseased for 

 some time. 



