Weir: Introduction of Wood-Destroying Fungi 61 



perate regions. This high temperature and consequent low gas 

 solubility, resulting in a deficiency of dissolved oxygen in soil solu- 

 tions and therefore in cell sap, might make tropical wood less 

 aerated. Abundant decaying organic matter resulting in a soil 

 solution with a low oxygen and a high carbon dioxide content 

 might possibly produce a ceh sap with the same unfavorable gas 

 content. There is also a possibility of the heartwood of trees 

 remaining functional for a longer period than is the case in tem- 

 perate zones. This would reduce the gas content and prevent the 

 advance of the mycelium in the wood. This condition is an- 

 alogous to the observed behavior of mycelia of wood-destroying 

 fungi in the wood of resinous and non-resinous conifers, or in the 

 wood of broad-leaved species forming or not forming heartwood. 

 In trees with a pronounced heartwood, decay is usually very pro- 

 nounced, in contrast to those where the central cylinder remains 

 for a longer time functional ; that is, transporting soil solutions 

 to the crown. There are exceptions to this generalization. The 

 heartwood of birch, which remains functional for a longer time 

 than that of oak, is seriously rotted by Fomes ignar'ms (Gill). 

 The non-resinous heartwood of Abies grandis is uniformly rotted 

 by Echinodontium tinctorium E. and E. Undoubtedly the re- 

 quirements of fungi differ to the extent that whereas one species 

 may find the non-resinous heartwood of Abies, for example, 

 favorable, as in the case of Echinodontium, the fungus will not 

 develop in the wood of pine or larch. In the case of Abies and 

 Echinodontium we may assume that the gas present in the heart- 

 wood of the host may be of a higher oxygen ratio than is the case 

 in those trees which it will not attack. To understand the par- 

 ticular conditions which govern the relations of host and fungus 

 is a problem for the future, and is of great practical importance. 



Tropical Wood-destroying Fungi in the Temperate Zone 



The reason for contrasting the conditions of growth between 

 the tropics and temperate zones is by way of introduction to the 

 idea that the wound fungi^ of tropical or foreign timber trees 



5 In the writer's opinion the term " wound parasite " as it is ordinarily- 

 employed is misleading. The parasitism of but few wood-destroying fungi 



