ADDENDA 563 



to be a true parasite, and the cause of root rot of tobacco. 

 This disease has assumed very serious proportions in the 

 United States, many instances being known where the entire 

 crop of seedlings raised by a farmer had to be discarded 

 because of the root rot caused by Thielavia. The diseased 

 area at the present time is confined to Connecticut. 



When plants are attacked in the seed-bed when quite 

 young, the seedlings may ' damp off' when not more than one- 

 third to half an inch high, the fungus attacking not only the 

 root but also the stem up to the cotyledons. When the 

 disease is not so virulent the root only is attacked, the 

 injury usually commencing at the end of the taproot and 

 gradually working upwards until the entire root-system is 

 destroyed, and, as this takes place, the plantlet usually puts 

 out numerous lateral roots. These serve the seedling for 

 some time, but eventually become diseased and the plant 

 perishes. 



The ascospore stage is said to occur in abundance on old 

 diseased roots of tobacco, and is borne in the midst of the 

 conidial forms. Carefully conducted experiments proved 

 Thielavia to be a true parasite. 



The author's summary as to the conditions conducive 

 to serious injury from root-rot are : 



(1) Infection of the seed-bed or the field with Thielavia 

 basicola. 



(2) A fairly heavy soil rich in humus. 



(3) Excessive fertilisation. 



(4) Heavy watering in the beds. 



(5) Lack of ventilation in the beds. 



The sterilisation of infected seed-beds by the methods 

 herein described (preferably by steam) furnishes an effective 

 means of preventing disease. 



Gilbert, W. W., U.S. Dept. Agric., Bureau of PI. Industry, 

 Bull. No. 158 (1909). 



Black rot of grapes. This disease, caused by Guignardia 

 bidwellii (Viala and Rav.), which proves such a scourge in 

 vineyards in the United States, has occupied the attention of 

 Dr. C. L. Shear for the past three years, with the result that 

 spraying experiments prove that the most serious epidemics 

 of black rot can be satisfactorily controlled by thorough and 

 proper methods of spraying. It has also been found that 



