150 DISEASES OF TROPICAL PLANTS CH . 



and from Northern and Eastern United States as far 

 south as North Carolina. Although it has not been 

 reported from tropical countries, its character is such 

 that the writer sees no reason why it should not appear 

 in some of the tobacco-growing districts of the tropics, 

 at any time, and for that reason this discussion is given. 

 Its wide range of host plants increases the danger 

 of transmitting it from place to place, and makes it 

 much more difficult to combat. 



The disease is due to a fungus, Thielavia basicola, 

 Zopf. (page 47), which produces an abundant inter- 



Fio. 62. Tobacco seed bed. (Photo by W. T. Home.) 



The left half of the bed on untreated soil and most of the plantsikilled by "damping off" j 

 fungi. The right half sterilized soil. 



cellular septate branching mycelium which somewhat 

 resembles the mycelium of Rhizoctonia. The roots of 

 the diseased plants are abnormal, and so weak that 

 when the plant is pulled up, they are frequently torn 

 off, leaving nothing but the stub. New roots are 

 frequently formed above the point of injury, and the 

 plant may continue to make a stunted growth or may 

 die. The roots may be rough and brown, and the inner 

 tissues are frequently red in colour. The disease is 

 most severe in the seed beds, and appears to thrive 

 best where the drainage is poor and the soil alkaline 

 in character. 



The seed beds should be treated as for other seed- 

 bed rots, care should be used in selecting nothing but 



