WILT-DISEASES OF TOBACCO. 



221 



devoted to a description of the signs of the disease and to statements of the numerous ways 

 in which the organism may penetrate the plant, the latter being conclusions derived from 

 field observations. The disease was believed to enter the plant only through wounds, 

 generally of the root or stem under ground, but also sometimes above ground. Many 

 possibilities are described. The organism is stated to be a coccus, measuring about &n in 

 diameter. It was not named, nor were many of its biological peculiarities described. It 

 is stated to issue from the plant as a dark brown slime, but to be grayish-white on agar 

 and to be actively motile in the plant. On plate-cultures it formed fused colonies with an 

 irregular wavy border. It stained readily with carbol-fuchsin and alkaline methylene blue. 

 The external signs in the tobacco plant are sudden wilting of the foliage, pale green 

 spotting and then brown spotting of certain foliar portions, especially the "ears" of the leaf, 

 general yellowing and death of the lower leaves and a local black stain in external portions 

 of the stem, especially toward the base. The brown spots on the ears of the leaf are said 

 to be a sure sign of the disease. The internal signs are a brown or black stain in the vas- 

 cular tissues (from 

 which on cross-sec- 

 tion a brown bac- 

 terial slime issues 

 abundantly), and 

 marked staining of 

 the pith, which is 

 usually found to be 

 badly disorganized, 

 so that in stems 

 attacked for some 

 time the whole 

 central portion be- 

 comes a slimy mass. 

 Such stems are 

 easily crushed be- 

 tween the fingers, 

 although externally 

 they may not show 

 any or much indi- 

 cation of disease. 

 The bacteria mul- 

 tiply most rapidly 



in the large intercellular spaces of the pith, less rapidly in the wide xylem vessels, where 

 the cross-walls act as hindrances. The phloem part of the stem ordinarily is not greatly 

 injured. The amount of starch in the vicinity of attacked tissues appeared to be notice- 

 ably less than in sound cells. The root-system is usually occupied by the bacteria, and 

 frequently stained dark brown. In bad cases the secondary roots are not well developed. 

 The underground part of the stem was often rotted badly. Eel-worms and an insect 

 (larva of the family Tineida?) causing galls on the stem at the surface of the earth were 

 believed to play a considerable part in paving the way for infection. It is also stated that 

 the removal of the lower leaves at the time of planting, and various other practices of the 

 coolies, favor the distribution of the disease. Sometimes the plants set out by one coolie 

 will be badly attacked, while those set out by his neighbors will be free from disease or 

 nearly free. The disease is said to be most serious on heavy lands, while on mellow ground 



*Fig. 115. Tomatoes following tobacco in a North Carolina field. The tobacco contracted the Granville wilt 

 and the tomatoes set in place now show the same disease. (From a photograph by Dr. F. L. Stevens.) 



Fig. 115. 



