DAMPING OFF. 



' ' Damping off " is a disease of seedling plants which rots or 

 disintegrates the tissues at the surface of the ground. The tissues 

 thus changed weaken, lose their firmness and supporting power, 

 and the seedling falls prostrate on the soil. The disease is wide 

 spread and sometimes very common. It occurs not only in gar- 

 dens and fields but is a very frequent attendant upon the culture 

 of seedling plants in the forcing house or bed. The trouble is 

 favored by damp soil, comparatively high temperatures, and 

 humid atmosphere. 



The term "damping off" is therefore indicative of one of the 

 attendant conditions of the soil inducing the disease. While this 

 popular expression is thus far significant of the trouble it is by no 

 means the exact statement of the case. The plants do not damp 

 off because of the abundant damp or moisture in the soil. The 

 dampness encourages the growth of minute parasitic plants, not 

 visible to the unaided eye, which pierce the seedling, feed upon 

 its substance and set up disintegration processes which result in 

 the death and collapse of the affected parts. Soon after the plant 

 falls the dissolution of the tissues near the surface of the ground 

 has usually proceeded so far that communication by the ordinary 

 physiological processes of life is cut off, and the plant then with- 

 ers and dies. While damping off is due to the action of minute 

 fungus parasites, it is by no means caused by one and the same 



Frontispiece. This is from a photograph of an experiment to show the 

 parasitic nature of the Artotrogus debaryanus (Hesse). Before planting the 

 cucumber seed the pots were* filled with soil which was thoroughly wetted 

 and then steamed in the steam sterilizer for several hours on three successive 

 days in order to kill all the organisms. The seed was then planted and when 

 just coming up some plant tissue with freshly developed stages of the fungus 

 was placed by the seedlings in pots 5, 6, and 8, while pot 7 was left as a 

 check. The result can be easily seen in the photograph, the check plants 

 remaining unharmed while all the plants in 6 are killed and only one re- 

 mains healthy in each of 5 and 8. 



