PROCEEDINGS OF THE ACADEMY AND AFFILIATED 



SOCIETIES 



THE BOTANICAL SOCIETY OF WASHINGTON 



The 82d meeting was held at the Cosmos Club October 17, 1912. 

 Mr. W. E. Lamb of the Forest Service was elected to membership. 

 The following papers were read: 



The cotton of the Hopi Indians: F. L. Lewton. This paper will be 

 published in full in the Smithsonian Miscellaneous Collections. 



A botanical trip to the Sevier Forest, southern Utah: W. W. Eggles- 



TON. 



Damping-off of coniferous seedlings: C. P. Hartley. With the 

 exception of the cedars, damping-off of seedlings is a serious hindrance 

 to the raising of conifer seedlings. Surfacing beds with gravel tends 

 to decrease the trouble. The disease is generally worst under moist 

 conditions, but a well drained nursery in dry climate in southwestern 

 Kansas has suffered especially heavy loss from damping-off parasites. 

 No positive control method has ever been developed for general use. 



In western porous soils damping-off is simply a root-rot of very 

 young seedlings, which may attack at any point from the ground sur- 

 face to several inches below. Seedlings several weeks old may have 

 the younger parts of their roots rotted and yet survive. 



Pythium debaryanum appears to be the most dangerous parasite in 

 western nurseries. Rhizoctonia sp., Fusarium sp., and probably Tricho- 

 derma lignorum, also cause damping-off. Pythium and Rhizoctonia 

 have been successfully inoculated on autoclaved soil, but inoculations 

 do not succeed uniformly on unsterilized soil, due probably to com- 

 petition of bacteria and other fungi. Rhinzoctonia loses parasitism in 

 culture and different strains vary greatly in virulence. 



All active Pythium in nursery soil can be killed very cheaply by 

 means of fungicides. Heat, and fungicides which break down soon 

 after application, such as mercuric chloride, or acids and copper salts 

 followed by lime, are not effective in the west, because Pythium often 

 reinfects such disinfected soil, running thru it rapidly before seedlings 

 raised on it develop resistance. This reinfection at least sometimes 

 takes place thru the air, and is difficult to prevent under nursery con- 

 ditions. Excellent results have been obtained by treating beds before 

 seeding with sulfuric acid and formalin, and on alkaline soils with 

 zinc chloride and copper sulfate. These fungicides seem to leave a 

 slight residue in the soil which protects against reinfection. This 



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