10 BULLETIN 496, TJ. S. DEPARTMENT OF AGRICULTURE. 
Different groups of fungi seem to have adapted themselves to 
certain growth conditions. For instance, Stereum rameale and S. 
hirsutum were usually found only on the twigs and small branches, 
while jS. iMbbrinum and S. versifoi v me occurred mainly on twigs and 
branches 2 inches or less in diameter. None of these four fungi were 
found attacking large limbs and trunks of the felled trees, while S. 
fasciatum, very common on stumps and trunks, rarely occurred on 
branches less than 3 inches in diameter. None of them were found 
growing on timber which was entirely shaded from the sun. 
The fungi which rot that portion of the branches lying in actual 
contact with the ground under the brush piles belong to an entirely 
different group. Such fungi apparently need a large supply of 
moisture and probably enter the wood from mycelia already growing 
and ramifying in the leaf debris in the soil. This group of fungi 
includes those which are normally found attacking wood partially 
or entirely buried in the soil, such as stumps and posts. 
WHY BRUSH IN THE CENTER OF THE PILE DOES NOT ROT. 
Why the fungi which are found attacking the limbs exposed to 
the sunlight will not usually attack the brush in the center or bottom 
of the piles when protected from the sun's rays is not known. Ap- 
parently temperature and moisture are not the only prominent fac- 
tors controlling fungous growth and activity in nature. Is it pos- 
sible that sunlight is a factor in the germination and growth of 
wood-rotting fungi in their natural habitats? 
In a previous article by the writer, 1 the theory was advanced that 
the reason why the brush in the center and bottoms of the piles in 
the semiarid regions of Arizona and New Mexico did not rot was 
due to temperature conditions prevailing in the high altitudes. That 
the temperature in Arkansas could be a prominent factor in the 
rotting of the brush, or, rather, in the lack of the rotting of the brush 
in the middle of the piles, seems hardly possible, since the tempera- 
ture there is sufficiently high during a large portion of the year for 
fungous mycelia to grow vigorously, provided the other factors 
necessary for fungous growth are also present. 
The precipitation in Arkansas is sufficient to supply all the mois- 
ture necessary throughout the entire brush pile for the active growth 
of wood-rotting fungi. It seems, therefore, that enough moisture 
would persist in the center of the piles for the brush to rot at least 
as rapidly as the pulled brush. The fact that twigs and branches in 
the center of piles large enough to be shaded from the rays of the 
sun were the only ones not rotted seems to indicate that sunlight may 
possibly play a part in the rotting of the brush, not only in Arkansas, 
iLong, W. H. Op. cit., p. 395-396. 
