402 
AMERICAN JOURNAL OF BOTANY 
[Vol. io, 
The mycelium of Lenzites trabea was decidedly the most resistant to 
heat, more especially dry heat. It was killed in 12 hours of exposure to 
105° C., but survived one day at ioo° C., 3 days at 90° C., 6 days at 8o° C., 
and 19 days at 70° C. The greater resistance of the mycelium of this 
species was naturally attributed to the possible presence of some resistant 
spores formed within the wood, but repeated examinations of wood infected 
with pure cultures of this fungus have not yet revealed the presence of 
secondary spores, although both oidia and chlamydospores are present in 
cultures upon agar media. The mycelium of the least resistant of the five 
(Trametes serialis ) succumbed after 10 days’ exposure at 6o° C., 4 at 70° C., 
2 at 8o° C., and I at 90° C. The thermal death points at dry heat for the 
other three fungi lie nearer to those of Trametes serialis than to those of 
Lenzites trabea. 
With moist heat, irregularities were more common and several repetitions 
were necessary to gain an idea of the resistance of the various fungi. Both 
Lenzites trabea and Lentinus lepideus in most cases survived 3 days at 44 0 C., 
and for varying periods up to 52 0 C. Trametes carnea in part resisted 48° C. 
for 24 hours, and in one case 52 0 C. for 12 hours. In these latter tests, 
however, growth occurred in only 2 or 3 tubes. Lenzites sepiaria survived 
no more than 12 hours at any of the temperatures of moist heat tried, and 
in one of the two tests at 52 0 C., growth occurred in only 1 of 10 tubes. 
The delaying effect of the more severe conditions, either of length of 
exposure or of degree of heat, in the growth of the mycelium from the test 
pieces on to the agar, was quite noticeable in four of the fungi, but less so in 
Lenzites trabea. This species responded to the test-tube conditions almost as 
well after periods of heat as in control tests. The growth in the tubes was 
slower in appearing, the more rigorous the exposure. Whereas a good 
culture may be obtained in 3 or 4 days from unheated wood such as used 
in these tests, growth from the more severely heated blocks was delayed 
until 3 weeks or 25 days for four of the fungi. If the mycelium in a block 
was ever to grow, it always appeared within a month. 
Bearing of these Results upon Heat Treatment 
of Timbers in Buildings 
The tests described in this paper were not made with the idea of obtaining 
practical results regarding the possibility of checking decay in buildings. 
They were intended simply as preliminary experiments and to be used as a 
guide in more extended work upon larger pieces of wood. However, even 
with the small blocks used, the results are so striking as to be worthy of 
discussion and useful in forming certain conclusions. 
These results will apply very well to i-inch stock, which is usually planed 
down to | inch, because the difference in the time of heating the f-inch and 
f-inch material would be slight. It is quite certain that heat would act 
more slowly upon mycelium in large beams and planks than it would in the 
