Sick Soils 17 



the cold frame as well as in the field. It is induced 

 by the presence of definite parasitic fungi, which 

 thrive best in overwatered soils, and when the green- 

 house is kept at a comparatively high temperature 

 with poor ventilation. Damping off is also favored 

 by thick sowing and too much shade in the seed bed. 

 Symptoms of Damping Off. Every experienced 

 grower knows the disease when he sees it. Seed- 

 lings freshly damped off are soft and water soaked 

 at the base of the stem. If they are pulled they 

 often break off easily. A more careful examination 

 shows that the root system is entirely decayed, al- 

 though the upper part of the stem and leaves may 

 still be green, and also possibly fresh. The degree 

 of prostration in the seedlings is determined by the 

 amount of moisture in the soil. If it is slight, the 

 seedlings will become flabby and wilted before they 

 topple over. With a high moisture content, they 

 are more firm, but become prostrate as soon as in- 

 fection sets in. The trouble usually begins in spots 

 in the bed, thence spreading in every direction. 

 Damping off is usually caused by several fungi, the 

 chief of which is Pythium de Baryanum Hesse. The 

 organism was first named and described by Hesse in 

 1874. Ward * found it to be a very prevalent para- 

 site in the garden soils of Europe. In America the 

 fungus was first recognized as of great economic im- 

 portance by Atkinson.t The seedlings of most 



•Ward, M., Quart. Jour. Micros. Soc. New Ser. 22: 487, iXij. 

 t Atkinson, G. F., New York (Cornell) Agr. Expt. Sta. Bui. 94: 

 233-272. i«9S- 



