DAMPHSTG-OFF IlsT FOEEST NURSERIES. 57 
experiments the losses were heavier in the Rheosporangium pots. 
Especially in experiments 61 and 62A the evidence indicates very 
strongly that both germination loss and subsequent damping-off of 
the seedlings which come up can be caused by inoculation with Rheo- 
sporangium on jack pine under favorable inoculation conditions. It 
is, however, obvious that in all of the experiments the parallel in- 
oculations with Pythium debaryanum gave much more positive re- 
sults. The Pythium was active under conditions in which the Rheo- 
sporangium gave no evidence whatever of parasitic capacity. It 
furthermore appears that the two strains of Rheosporangium, though 
probably identical originally, differed in virulence at the time of 
their comparison in these experiments. The greater virulence of 
strain 351 was quite distinct in most of the comparative tests on beets 
as well as on pines. The possibility that the original culture was 
really a composite of two or more strains, of which different ones 
survived in ,the subcultures kept at Washington and Madison, re- 
spectively, seems worth considering. Such an accident might also 
have been responsible for the divergence of Pythium strains 131 and 
295 referred to in another section. 
Further evidence of the parasitism of Rheosporangium was ob- 
tained in inoculations with cultures reisolated from seedlings killed 
by the original strains in experiment 62. Typical Rheosporangium, 
identified by presporangium formation, was easily recovered from 
the damped-off seedlings in pots of pines only, those of beets only, 
and the pots in which both hosts were sown. The recovery of a 
virulent Pythium strain from a single one of the pots inoculated with 
the weaker Rheosporangium shows that despite the absence of dis- 
ease in the controls a slight amount of contamination did occur. 
However, the comparative ease with which the Rheosporangium was 
isolated from seedlings in other pots inoculated with it and the fact 
that it has never been obtained in the numerous cultures made from 
controls and from pots inoculated with other organisms leave little 
room for doubt that the strains isolated were really recoveries of the 
Rheosporangium used in the original inoculations. The results of 
reinoculation with these strains are shown in Table VII. 
From Table VII and by comparison with Table VI it appears — 
(1) That in one experiment each on jack pine and red pine the reisolated 
Rheosporangium strains gave positive results. In a second experiment on jack 
pine (No. 67) the difference between the Rheosporangium pots and the con- 
trols was not significant. 
(2) That, as in Table VI, the Pythium strains used proved on the whole 
decidedly more parasitic than the Rheosporangium strains. In experiment 66 
this is not shown by the percentage of seedlings damped-off, but is sufficiently 
evident when the germination loss as well as the subsequent damping-off per- 
centage is considered, the survival being here, as in most other cases in which 
