Feb 15, 1925 
I inoculation o f Coniferous Stems 
333 
RESULTS OF THE PRESENT INVES¬ 
TIGATION 
Pythium Debaryanum 
The results secured by inoculating 
seedlings of Pinus resinosa Ait., P. 
banksiana Lamb., and Picea engelmanni 
Engelm. with Pythium debaryanum by 
the platform method are given in Table 
II. P. debaryanum caused some damp¬ 
ing-off in all but three inoculated units, 
all three with the same weak line (No. 
743). Regardless of its substratum, P. 
debaryanum caused more than half of 
the seedlings to damp-off. In the case 
of Pinus resinosa both rice mush and 
corn-meal agar inoculum were tested. 
In more than three-fourths of the tests 
the fungi when grown on rice mush 
caused more damping-off than in the 
same tests when grown on corn-meal 
agar. The latter were not more de¬ 
structive in a single case. Since the 
mycelial development was much more 
luxuriant on the mush, it seems that 
virulence may be associated with vigor 
of growth. Figure 2 shows this graph¬ 
ically. The lines isolated from conifer¬ 
ous hosts were no more virulent than 
those isolated from other hosts. On 
the whole, the P. debaryanum lines were 
more destructive than any of the other 
fungi, with the possible exception of 
Bolrytis cinerea. The control seedlings 
damped-off very little. 
An attempt was made to get some 
idea of the relative susceptibility of the 
various hosts to Pythium debaryanum 
by comparing the percentages damped- 
off by the eight lines tested on all three 
hosts with rice mush as a substratum. 
The figures secured in this way vary 
slightly from those given in Table II, 
where all lines were included, but for 
practical purposes they are the same. 
For Pinus resinosa the damping-off was 
93 per cent; for P. banksiana, 98 per 
cent; and for Picea engelmanni, 96 per 
cent. Thus it seems that all three host 
species are highly and practically 
equally susceptible to P. debaryanum 
under the conditions of these experi¬ 
ments. A comparison of results se¬ 
cured with the standard Pythium line 
confirms this conclusion. 
Some of the Pythium debaryanum 
lines were used in miscellaneous small 
experiments with other coniferous seed¬ 
lings. This fungus caused 26 out of 30 
seedlings of Abies nobilis Lind, to damp- 
off in an experiment in which 1 out of 
10 control seedlings damped-off. Be¬ 
cause of the difficulty of germinating 
the Abies seeds it was impossible to 
conduct other or larger experiments. 
13952—25f-4 
For the same reason only small experi¬ 
ments were conducted with Pinus 
caribaea Morel. There was no damp¬ 
ing-off among the 20 control seedlings, 
although 18 out of the 30 inoculated 
ones damped-off. One out of 10 con¬ 
trol seedlings of Pseudotsuga taxifolia 
(Lam.) Brit, and 15 out of 20 inoculated 
ones damped-off. The above tests are 
purely preliminary but seem to indicate 
that Pythium debaryanum can cause 
damping-off of A. nobilis, Pinus cari¬ 
baea, and Pseudotsuga taxifolia. The 
first two are new hosts for P. debarya¬ 
num, and heretofore it had not been 
definitely proven that the last named 
is a host for it. 
Two small test tube experiments and 
two pot experiments in which seedlings 
of Pinus resinosa were inoculated at the 
ground level with three of these Pyth¬ 
ium debaryanum lines confirmed the 
results secured with the same lines by 
the platform method. 
Other Phycomycetes 
The results secured by inoculating 
seedlings of Pinus resinosa and P. 
banksiana with miscellaneous Phyco¬ 
mycetes by the platform method are 
also given in Table II. 
RHEOSPORANGIUM APHANIDERMATUS 
The two available lines of Rheos - 
porangium aphanidermatus were very 
parasitic to both species, being approx¬ 
imately as virulent as Pythium debar¬ 
yanum itself, and decidedly more 
virulent than most of the other fungi. 
On the whole it was more active when 
grown on rice mush than when grown 
on corn meal agar (fig. 2). 
MUCOR RACEMOSUS 
This species was tested on only 20 
seedlings in an experiment in which 
the standard fungi were less virulent 
than the average, and caused no 
disease at all. An unknown Phyco- 
mycete, which formed only small 
irregular chlamvdospores, caused no 
disease and the spiny Pythium, which 
has been referred to the species artotro- 
gus caused no appreciable damping-off. 
In Hartley’s (5) experiments P. arto - 
trogus caused somewhat more damping- 
off than in the writer’s experiments. 
pythiacystis citrophthora 
To avoid the danger of establishing 
this exotic form in the eastern United 
States, it was used in a small test-tube 
