4-4 BTLLETIX 934, r. S. DEPARTMENT OE AGKICDJLTUBE. 
it proved difficult to keep the control pots entirely free from damp- 
ing-pff. Cultures from seedlings which damped-off spontaneously 
in control pots indicated that Pvthium as well as Fusarium mav be 
introduced by accident, even when insects, birds, and rodents are ex- 
cluded. This agrees with the evidence of Hofmann (77) that 
Pythium debaryanum is sometimes disseminated by wind, despite 
its apparent lack of adaptation to wind distribution. It is also in- 
dicated, however, that unheated tap water increases damping-off 
when used on control pots and probably carries this semiaquatic 
fungus. Xotwithstanding infections in the controls of a number of 
the experiments, it is believed that the large number of pots whose 
results have been considered in drawing conclusions, the fact that the 
Pvthium pots lost more heavily than the controls in every one of the 
16 experiments, and the magnitude of the differences between both the 
emergence and subsequent damping-ofT figures for the inoculated pots 
and the controls in most of the experiments establish the parasitism 
of the fungus in inoculation on autoclaved soil without it being neces- 
sary to present all the evidence in detail. The pot series which in- 
volved reisolation and reinoculation (Table III), together with the 
results given for other purposes- in Tables V and VI. seem sufficient 
by themselves to establish a parasitic relationship. 
P.EISOLATIOX A^D EEIXOCVLATIOX. 
In a number of the experiments dead seedlings in the inoculated 
pots were examined and typical Pvthium hyphae and spores were 
found. In three of the experiments in which the controls remained 
entirely free from disease up to the time the experiment was closed, 
reisolations and reinoculations were made in accordance with the 
usual rules of proof. The results are given in Table III. 
From Table III it will be seen that five strains reisolated from 
Pinus banksiana and one strain reisolated from P. ponderosa gave 
positive results in pots of P. banksiana and P. reshwsa. In addition 
to the reinoculations shown in the table, the strain reisolated from 
P irais ponderosa (Xo. 33S) was again reisolated in duplicate from 
P. banksiana in experiment 62. and both these secondary reisolations 
gave cultures which were parasitic on P. banksiana and P. resinosa 
in subsequent inoculations. 
That the organisms reisolated were actually the same as those used 
in the initial inoculation is indicated not only by the absence of dis- 
ease in the control pots of experiments 58 and 62. but by the distinc- 
tive characters of some of the strains. In general, cultures reisolated 
from strongly parasitic initial strains were themselves strongly 
parasitic and vice versa. This is shown by comparing the figures for 
the initial and reisolated strains, as shown in Table IV. Each figure 
represents the average results in 10 pots of jack pine and 5 of red 
