WILT-DISEASES OF TOBACCO. 223 



In tobacco already topped the slime-disease often shows strikingly on the above-ground plant, so 

 that the top is said to be water-soaked (ingeregend). 



If one cuts the stem of a slime-sick plant crosswise there then appear quickly on the cut surface 

 little brown drops, which slowly become greater by fusion and occupy just the place of the vascular 

 ring. If one examines the physical condition of these drops they are seen to consist of a slimy sub- 

 stance which may be stretched out in threads. 



If one examines microscopically the leaf-spots of the slime-sick tobacco on cross-section, then 

 one sees that the parenchyma of the spot is completely changed. The cell-walls are dissolved and 

 the chloroplasts wholly disorganized, while in their place a mass of bacteria fills the spots of the 

 attacked leaf-blade. If a section is made across an attacked stem we see that the walls of the vas- 

 cular bundle, and also of the woody parenchyma bordering the same, are colored dark brown, some- 

 times even black, while the lumina of the xylem vessels show a partial or total occlusion. This occlu- 

 sion consists partially of the massing of bacteria with their disorganization products and partially 

 of bladder-formed swellings from the surrounding parenchyma cells, that is, tyloses which have grown 

 into the interior of the vessels. This abnormal filling of the water-paths causes naturally a stoppage, 

 on account of which the sap-stream is noticeably hindered and finally interrupted. The necessary 

 consequence of this is that water-need appears, which is shown by the wilting of the part of the plant 

 above ground. 



The inclination to this formation of tyloses is caused by a bacterium (Bacillus solanacearum 

 .Smith), which by means of many sorts of external wounds is given an opportunity to enter into the 

 interior of the plant. When once entered into the xylem vessels the vessel wall is through them in 

 some places partially absorbed, so that the above mentioned tyloses are formed. 



The slime-disease described here is altogether a secondary phenomenon, which is made possible 

 by external wounds. 



In by far the most cases the injury of the plant takes place either on the root or on the stem con- 

 cealed underground. In the latter case I mean the stem part which has been covered with earth by 

 heaping up the ground. 



The woundings may be due to many and very different causes. In the first place should be 

 mentioned wounds due to plant and animal parasites. Among the first named I reckon chiefly the 

 parasitic molds, especially Phylophthora nicotianae. Some of the principal animal parasites are the 

 injurious soil insects, for example, eel-worms (Heterodera radicicola) and thick bellies* [Glechia sola- 

 nella Boisd. (G. tabacella Reg.)]. 



In the second place are to be mentioned the mechanical injuries which during culture may be 

 brought about by various means, such as pulling up the seedlings, transplanting, hilling, topping, and 

 removal of suckers. 



Finally, an injurious chemical and physical soil-condition is not least active in making the under- 

 ground plant parts susceptible to infection, the most important of which is poorly cultivated and 

 badly drained ground. This does not allow the roots to develop normally, and on account of the 

 stagnating water they go easily over into decay. 



Through all the above summed up circumstances the Bacillus solanacearum, present in the 

 ground, is given the opportunity of penetrating into the plant through the injured places, so that the 

 sickness induced thereby is a secondary process for the occurrence of which occasion may have been 

 given in various ways, but always with the same external signs. 



The spread of this disease in the field is very easily caused during the care of the tobacco, as well 

 by the coolies themselves as by their tools. 



In the plant itself the spread of the infection is assured as soon as the bacteria have reached the 

 vascular bundles. With the rise of the sap-stream from the root-system the bacteria are carried 

 along [?] to the parts of the plant above ground, where the signs of the disease appear in the various 

 organs. 



Bacillus solanacearum Smith is elliptical in form, of middle size, ordinarily 1.5 to 3 times as long 

 as broad (1.5M long and 0.5^ broad), but very variable, according to age and cultural condition. 



Pure cultures are easily made upon agar plates. In the beginning this bacterium forms on the 

 surface of the nutrient substratum small, round, dark brown colonies,! which slowly extend concen- 

 trically. Mixed in with these round colonies come often also lens-formed colonies, but both are made 

 up of Bacillus solanacearum. These variable ways of growing of the self-same bacteria are a conse- 

 quence of the location of the colonies. If they are buried in the agar then they grow slowly toward 

 the surface on account of lack of oxygen. 



*So called because they produce a swelling or gall on the stem at the surface of the earth. 



fThis is probably an error, unless we are to assume the organism different from Bacterium solanacearum. Van 

 Breda de Haan says grayish-white on agar, and this, so far as my own observation goes, is always the initial color of 

 B. solanacearum, the colonies of which become brown only after some days or weeks. 



