10 BULLETIN 496, U. 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 S. umbrinum and 8. versiforme 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 w y ill 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. 



