DAMPING-OFF IX FOREST NURSERIES. 55 



under ordinary nursery conditions is yet to be proved. The results 

 in inoculations on disinfected soil, together with the frequency with 

 which the fungus has been isolated from seedlings in the nurseries, 

 lead the writer to believe that it is an important cause of disease in 

 the seed beds. Further experiments on unheated soil, however, are 

 considered desirable. 



RHEOSPORANGIUM APHANIDERMATUS. 



CULTURAL STRAINS. 



A culture of a parasite on radishes and sugar beets, described by 

 Edson (39) under the above name, was obtained from him, and an- 

 other strain, shown by Edson's records to be a subculture from the 

 same original strain, was furnished by the department of plant pathol- 

 ogy of the University of Wisconsin. In parallel cultures on solid 

 media this fungus proved in many ways remarkably like Pythium 

 debaryanum, reacting in practically the same way to the different 

 media on which it was grown both in relative growth rate and in 

 spore production. Mycelium, chlamydospores, oogones, antheridia, 

 and oospores are not recognizably different from those of Pythium 

 debaryanum. The oospores have seemed on the whole slightly larger 

 and the mycelium a little more inclined to aerial growth than most 

 of the PytMum debaryanum strains, but neither difference was suffi- 

 cient to have diagnostic value. Swellings of the hyphse occurred at 

 points in contact with glass, just as with Pythium debaryanum (PL I, 

 figs. 5 to 7). 



In liquid cultures the Rheosporangium was readily distinguished 

 from Pythium by the formation of the presporangia described by 

 Edson. Autoclaved cylinders of turnip, 15 to 20 mm. long, cut with 

 a 5-mm. cork borer, proved convenient bases for growth of both 

 Rheosporangium and Pythium in water culture and quite as satis- 

 factory as sterilized beet seedlings. Presporangia were also pro- 

 duced in autoclaved soil, and in a single lot of corn-meal agar they 

 were formed abundantly in the agar in Petri dish cultures. In none 

 of the writer's cultures, either with flies, sugar-beet seedlings, or 

 turnip cylinders as nutrient bases, were mature escaped sporangia 

 or swarm spores commonly produced. 



The Rheosporangium was not obtained in any of the numerous 

 cultures made from coniferous seedlings or from seed-bed soil. 



INOCULATION EXPERIMENTS. 



The Rheosporangium cultures above referred to, strain 229 fur- 

 nished by Dr. Edson and strain 351 received from the University of 

 Wisconsin, were tested on pine and red-beet seedlings, with parallel 

 inoculations with Pythium debaryanum. The results appear in 

 Table VI. 



