DAMPING-OFF IN FOREST NURSERIES. 



63 



than half as rapid. Chlamydospores are mostly intercalary, at first 

 subspherical, soon becoming polygonal, and after a few days they 

 shrivel and exhibit thick, angular walls. In size the unshrunken 

 spores usually lie between 8 and 12 pi in diameter, but bodies as 

 large as 20 \i occasionally occur. Antheridia have not been observed, 

 and the shriveled bodies are not believed to be oospores, though the 

 observations made have not been sufficient to exclude such a possi- 

 bility. No other spore form was obtained in water culture, using 

 various nutrient substrata. In inoculation the strain from olive (the 

 "undetermined Phy corny cete" included in Table VIII) has given 

 negative or nearly negative results in three inoculation tests in which 

 other fungi gave positive results. In a test not included in the table, 

 in which Pinus ponderosa was the trial host, damping-off was slightly 

 higher in the inoculated pots than in the controls, but the difference 

 was apparently due to accidental infection with Botrytis and 

 Pythium debaryanum. As all the seedlings in pots inoculated with 

 P. debaryanum in this additional experiment were killed, the rela- 

 tive unimportance of this strain of the small-spored fungus was 

 further indicated. An additional test of both the olive strain and 

 the strain from soil was made by inoculating seedlings of Pinus 

 banksiana and P. ponderosa growing on filter paper in Petri dishes. 

 Some of these were kept wet with water, some with an inorganic 

 culture solution, and some with the inorganic solution plus peptone 

 and dextrose. Agar cultures were applied directly to the seedlings. 

 The seedlings inoculated with the small-spored fungus remained 

 alive as long as the control seedlings, while parallel inoculations with 

 Pythium debaryanum resulted in the early decay of the seedlings. 



Table VIII. — Results of inoculations with miscellaneous oomycetes on pines in 

 autoclaved soil at the time of sowing. 



[In all the experiments included in this table, the inoculum consisted of fragments of agar cultures 

 distributed with the seed at one side of each pot over about one-fourth of the pot area. The controls 

 received sterile agar in the same way J 





Num- 

 ber of 

 pots. 



Results. 



Experiment number, host, and inoculating fungus. 



Emerged. 



Damp- 

 ing-ofl. 



Survival. 



No. 66, Pinus banksiana: 

 Phytophthora sp.— 



Strain 358 , 



5 

 5 

 5 

 4 

 5 

 25 



5 

 5 

 5 

 5 

 5 

 23 



Per 5-pot 

 unit. 

 70 

 75 

 94 

 115 

 83 

 75 



96 

 88 

 99 

 102 

 98 

 87 



Percent. 

 30 

 28 

 16 

 14 

 9 

 -14 



1 

 3 

 

 2 

 

 5 



Per 5-pot 

 unit. 

 49 



Strain 372 



54 



Strain 375 •. 



79 





99 





76 





64 



No. 67, Pinus banksiana: 

 Pnvtophthora sp.— 



Strain 358. . 



95 



Strain 372 



85 



Strain 375.. . 



99 





100 





98 





83 



