46 BULLETIN 934, U. S. DEPARTMENT OF AGRICULTURE. 
liest report of pathogenicity (62), but have not been used as evidence 
in the present bulletin, though the contaminating bacteria in one of 
them, when tested independently, showed no evidence of parasitism. 
In all the experiments mentioned in the foregoing as giving positive 
results with Pythium the cultures used were apparently pure. 
Cultures from single chlamydospores should be reasonably easy 
to secure, part of the chlamydospores in water cultures being separa- 
ble from the mycelium by vigorous shaking, and further inoculation 
tests with cultures so obtained are probably desirable. The experi- 
ments so far conducted are believed to be sufficiently conclusive, how- 
ever, for all practical purposes. For isolation of absolutely pure 
lines of this or any other ccenocytic fungus, it is evident, as pointed 
out by Dr. W. H. Weston (146), that isolations should be made from 
the uninucleate swarm spores. For the determination of the bare 
fact of pathogenicity such a refinement would be superfluous. 
CEOSS-INOCULATIONS. 
The physiological identity of the Pythium attacking coniferous 
seedlings with the one which attacks dicotyledons is indicated by 
the results of several inoculation experiments. The last two experi- 
ments, one with jack pine and one with red pine for the host, are 
the most comprehensive and give results sufficiently decisive so that 
quotation of the corroborative evidence from earlier experiments 
is considered unnecessary. The results appear in Table V. Each 
unit consisted of five 3-inch pots except in the controls, in which 
23 pots were used in the jack-pine experiment and 18 in that with 
red pine. In the second experiment, separate records were kept of 
the survival in each pot, and the probable error calculated from the 
controls was less than two seedlings per pot for a single pot, less 
than 0.9 for a mean of 5 pots, and less than 0.5 for the mean of the 
18 control pots. While the number of controls was, of course, in- 
sufficient to furnish an exact basis for such a calculation, the small 
value found tends to confirm the impression .gained from inspection 
of the table that considerable confidence can be placed in the results. 
The difference appearing in Table V between jack pine and red 
pine in point of susceptibility to germination loss from Pythium 
agrees with field observations in Nebraska, the red pine at the Bessey 
Nursery, though on the whole more susceptible than jack pine to 
damping-off losses, having given indication of more resistance to the 
disease for the first week or two. Inoculations in other experiments 
on western yellow pine indicate that the strains which attack it are 
identical with those attacking jack pine and red pine. 
The conclusion reached from the cross-inoculation results is that 
the Pythium causing damping-off of the three species of pine men- 
