DAMPING-OFF IN FOREST NURSERIES. 61 



A species of Phytophthora was isolated by Mr. R. G. Pierce from 

 damped-off Pinus resinosa in Minnesota and used in four inocula- 

 tion experiments, the results of which appear in Table VIII. In the 

 first of these experiments unboiled water was used on the pots, and 

 mice obtained access to the pots of the second test. Probably as a 

 result of these things infection occurred in the controls in both cases, 

 and the results were inconclusive; in the later experiments these 

 two sources of infection were eliminated, and in experiments 68 and 

 72B the controls were free from disease. Parasitic activity was in- 

 dicated rather strongly in experiments 68 and 72 (on P. resinosa and 

 P. banksiana) and to a certain extent in experiment 66. In experi- 

 ment 67 it was evident that the Phytophthora was nearly or entirely 

 inactive. Comparison of the results in experiments 66 and 68 with 

 the results from inoculations with Rheosporangium aphanidermatus 

 in the same experiments (Table VII) suggests that the Phytoph- 

 thora may be better able to attack the pine from which it was isolated 

 than the Rheosporangium, while the latter fungus caused consider- 

 ably more destruction to Pinus banksiana than the Phytophthora. 

 Comparison of the results in the pots inoculated with Phytophthora 

 and those inoculated with Pythium debaryanum in all the experi- 

 ments indicates that the Phytophthora strains used were less virulent 

 than most of the strains of P. debaryanum and very certainly less 

 destructive than the most active strains of either P. debaryanum or 

 Corticium vagum. This species of Phytophthora has been reisolated 

 from damped-off Pinus ponderosa in experiment 72. 



Direct inoculations of the stems of seedlings of Pinus resinosa soon 

 after they emerge from the soil have so far confirmed the lack of 

 parasitism of Phytophthora cactorum and of the cultures of Phy- 

 tophthora sp. grown by the writer. The identity of this species has 

 not yet been determined. It is able to grow only about one- fourth as 

 rapidly as Pythium debaryanum on the medium which has been 

 used for isolation and may therefore be more common in the seed 

 beds than the small number of isolations by the planted-plate method 

 would indicate. However, its oospores, larger and darker than those 

 of Pythium debaryanum (usually over 20 ^ in diameter) , should have 

 been recognized in the routine microscopic examination of planted- 

 plate cultures had this species been frequently present, even if it 

 had not grown fast enough to get out ahead of the other organism 

 and allow isolation. It is not believed that it is common enough in 

 pine seed beds to be of importance, even if other strains should be 

 found more virulent than those which have been available. 



MISCELLANEOUS PHYCOMYCETES. 



A fungus, apparently referable to the somewhat indefinite Pythium 

 artotrogus (Mont.) De Bary, was isolated by Mr. Glenn G. Hahn 

 from Pinus resinosa in Michigan and from damped-off Pinus bank- 



