30 MISSOURI BOTANICAL GARDEN. 
very susceptible to the attacks of timber-destroying fungi 
while they are still parts of living trees, but as soon as 
they are cut from the trees not only does all further growth 
of that particular fungus cease, but the wood seems to be 
more or less immune for long periods to the attacks of the 
fungi which attack dead wood. Notable examples of this 
kind are the woods of the bald cypress and its near allies, 
the big trees, incense cedar and the various species of red 
cedar. The heartwood of all of these trees is destroyed 
(in some instances 90% and more of the living trees 
are affected) by fungi which do not grow after the wood is 
cut from the tree. Other trees, for instance the pines, 
have similar enemies, which grow only on live trees. The 
cessation of growth may possibly be due to the different 
moisture content of the wood of live trees, but this cannot 
be the sole factor, for felled trees donot begin to dry for long 
periods after cutting. The gases found in live trees may 
be different from those in the dead tree, both as to their 
composition and their tension. That there is considerable 
difference in this respect is shown by the readiness with 
which the fruiting organs of many of these fungi can be 
induced to form wherever a wound is made, admitting air.* 
A further factor which may be of a determining nature, is 
found in the products formed in the heartwood when ex- 
posed to the outside air; these are often made evident by 
a darkening of the wood. Differences in temperature 
probably occur. The intrinsic difficulties found in deter- 
mining the physical condition of the wood while in a live 
tree do not allow of any more definite statement than 
those made above. 
In this connection, the question arises, what are Polypo- 
rus rimosus, and the other fungi which grow on live trees, 
but not on dead wood of the same trees? Their substra- 
* von Schrenk, H. Some Diseases of New England Conifers. Bull. 
No. 25, Div. Veg. Phys. & Pathology U. S. Dept. of Agriculture. 48. 
1900. 
