Damping Off. 345 



sprinkling sulphur on the soil and in some cases sulphur at the rate 

 of one to thirty is mixed in the soil before sowing with good effect. 

 When the beds are badly infested Humphrey^° advocates the entire 

 removal of the soil, whitewashing the beds, and the introduction of 

 fresh soil. 



In houses heated by steam if it were possible to have, without too 

 great expense, a steam chest where the pots and seed pans which 

 are used could be placed and the soil thoroughly steamed for sev- 

 eral hours it could be sterilized, and the finer and more delicate 

 seedlings be grown then with little danger if subsequent care was 

 used to not introduce soil from the beds. In testing the virulence 

 of the Artoti'ogus deharyanus (Hesse), and of the sterile fungus, 

 several experiments have been made by steaming pots of earth, 

 growing seedlings in them and then inoculating some of the seed- 

 lings with the fungus while other pots were kept as checks, and all 

 were under like conditions with respect to moisture, temperature, 

 etc. The seedlings w^hich were not supplied with the fungus re- 

 mained healthy while those supplied with the fungus were diseased 

 and many killed outright (see frontispiece). 



Conclusions. 



Damping off is caused by the growth in the seedlings or cuttings 

 of fungus parasites which themselves are plants, but microscopic in 

 size. The plants when affected frequently present a paler green 

 <;olor. The tissues become soft at the surface of the ground, the 

 plant falls over and dies. ]S"o one fungus is concerned even in the 

 soft rot of seedlings. In related cases the plant may show a brown- 

 ish ulcer at the surface of the ground which frequently increases in 

 size until the plant is severed at this point and then dies. 



Too great a moisture content of the soil, air, high temperatures, 

 close apartments, and insufficient light not only favor the rapid 

 growth of the parasites but they also induce a weakly growth on 

 the part of the seedling so that it cannot so readily resist the disease. 



The parasites can grow and multiply on decaying vegetable mat- 

 ter which is in the soil. 



When once in the soil they can remain alive for months even 

 though the soil become dry or frozen. 



Soil used in seed beds or cutting beds should be free from de- 

 caying vegetable matter or care should be used that the matter is 

 30 Mass, State Agr. Exp. Sta. Bull. 402, 1891. 



