[Vor. 3 
450 ANNALS OF THE MISSOURI BOTANICAL GARDEN 
bark, and this seals the wounds to the exclusion of the 
fungus. We have found that the mycelium of L. saepiaria 
will not grow on 100 per cent resin plates because of the lack 
of nutrition, nor will the spores germinate on such a medium. 
In living trees, then, the pure resin covering the wounds 
serves a twofold purpose. It mechanically prevents the en- 
trance of the fungus, and excludes the air which might other- 
wise gain access to the interior of the tree more rapidly than 
under natural conditions. Resin does not exist in this high 
percentage, however, in the interior of wood, but is infiltrated 
into the lignified walls. Hence, there is still air in the lumen 
and food accessible to the fungus. Laboratory experiments 
reported below have shown that under these conditions the 
presence of resin has very little influence upon the growth of 
the fungus, at least up to 50 per cent resin by weight, which 
is considerably more than is found in any coniferous wood. 
A quantity of resin was extracted by means of benzol from 
longleaf pine wood (Pinus palustris). The resin was hard- 
ened at 65°С. until it was of a constant weight. This was 
used in making a resin agar, the basis of which was a 4 
per cent Thaxter’s glucose-potato-hard agar. The powdered 
resin was added to the agar while warm, emulsified by vigor- 
ous agitation, and then sterilized. Sterilization may be done 
in the Arnold sterilizer on three successive days, or if it is 
necessary to sterilize but once, autoclaving is satisfactory; 
but when autoclaved more than once the resin seems to be 
acid enough to hydrolyze the agar sufficiently to keep it from 
hardening. If the agar is removed from the autoclave while 
it is still quite super-heated and vigorously agitated while it 
is cooled by placing under the water tap from time to time, 
a very satisfactory emulsion of any percentage may be 
obtained. 
The agar was made up so as to contain 5, 10, 15, 20, ete., up 
to 100 per cent, of resin, which was plated out and after 
cooling was inoculated with squares of mycelium of L. 
saepiaria cut as suggested by Humphrey and Fleming (715, 
pl. 1). The inocula were 0.8 em. on a side. After 14 days of 
growth at 32° C. measurements of the diameters of the grow- 
