DAMPTNG-OFF TN FOREST NURSEPJES. 41 



formed, a few tests indicate that the fungus is very short lived, 

 sometimes dying in a month. On media on which spores are pro- 

 duced, transfers any time before the sixth month, and often as late 

 as the tenth month, start immediate growth on fresh media. This 

 is true even for strains which produce few or no oospores. The im- 

 mediate commencement of growth from cultures 3 or 4 months old 

 is taken as an indication that the new growth results from the 

 asexual spores, as oospores are commonly believed to require a rest- 

 ing period of five or more months before they are able to ger- 

 minate (5, 38). 



INOCULATION ON STERILIZED SOIL. 



Pythium debaryanum has been used in inoculation in pots of 

 recently autoclaved soil in 16 different series of tests. In 10 of these, 

 fragments of agar cultures were scattered over about one- fourth 

 of the area at the side of each pot when seed was sown ; in 2 of these 

 10 and also in 2 other tests some pots were inoculated over their 

 entire surface. In every one of these 12 heavily inoculated series 

 positive results were indicated by smaller emergence and where any 

 considerable number of sprouting seeds escaped the fungus by heavier 

 damping-off loss in the inoculated pots than in the controls. In 

 some cases the fungus killed all or practically all of the seed or 

 seedlings in the inoculated pots before they emerged from the soil. 



In a total of 7 series, part or all of the pots received lighter in- 

 oculations, consisting of one or two small fragments of an agar 

 culture placed just below the surface of the soil at the edge of each 

 pot. In 5 of these success was indicated. In the sixth and seventh 

 also of these lightly inoculated sets, there was more damping-off in 

 the inoculated pots than in the controls, but the difference was neg- 

 ligible. The damping-off caused by light inoculations was in general 

 distinctly less than that resulting from broadcast inoculations. To 

 sum up the evidence : Sixteen separate experiments were conducted 

 with Pythium debaryanum on pine seedlings in autoclaved soil, and 

 in every one fewer seedlings survived in the inoculated pots than in 

 the checks ; the difference in most of the experiments was large. 



Of the successful inoculation experiments — that is, those in which 

 the difference between the inoculated pots and the checks seemed 

 significant — 9 series included jack pine (Pinus banksiana) , 7 series 

 western yellow pine (P. ponderosa, Colorado and New Mexico seed) , 

 and 3 series red pine (P. resinosa). In addition to the pines, Doug- 

 las fir {Pseudotsuga taxifolia, Colorado seed) was grown in two large 

 plats in one of the earlier series, one being inoculated over its entire 

 surface with Pythium debaryanum. Because of the poor quality 

 of the seed in the test on Douglas fir, too few seedlings were obtained 

 to furnish a decisive test, but the difference in the emergence in the 

 inoculated plat and the control affords preliminary evidence that 



