&TJBBEB -IIEVEA, DtSEAS - 65 
It may not be out of place to discuss briefly the reason why smooth- 
barked trees are so readily injured by fire. 
The medullary rays of the wood cylinder extend through the true 
cambium into the phloem of the inner bast layer, terminating in 
the secondary op cork cambium of the outer cortex. Here, if the tree 
is young, are located lame masses of parenchymatous cells filled with 
chlorophyll and other delicate structure-. The primary rays, those 
having their origin in the pith, on entering the bast usually spread 
out in younger trees into triangular area- of delicate parenchymatous 
tissue which supply the food substances to the cells of the cork cam- 
bium. The^e ray cells are storage re-ervoirs of food and are chiefly 
concerned in transporting soluble food substances in a horizontal 
direction between the cortex and the inner wood cylinder. The food 
substances used in any part of the tree horizontally or tangentndly 
largely pass through the phloem, which is in intimate connection, 
as above noted, with the ray cells. "When the close relation bet' 
the cortex, the most vital part of the organization of the tree, and 
the ray cells of the wood and cambium is considered it is appreciated 
how fire injury to the former may work great injury to the life of 
the tree. 
Protoplasm is killed at a temperature not much over 50 G C: con- 
sequently, trees may be very seriously injured when heated but un- 
touched by flames. This type of injury may be difficult to detect 
until such complications set in as make the hidden wound apparent. 
An examination of severely heated or scorched trees showed that 
checks appeared in the cortex along the line of ray ceils leading 
directly to the cambium. If the cortex does not crack open, these 
concealed fire sears are not detected until attacked by borers or, 
as sometimes happens, an inward flow of latex causes the formation 
of rubber pads with a bulging of the dead cortex. In some trees 
examined the fire had been in direct contact with the cortex, which 
had fallen away for a distance of a foot or more on the injured parts. 
Probably the most immediate result of fire injury from the stand- 
point of what may be called disease is the appearance in the affected 
wood of chromogenic fungi. These fungi color the dead wood of 
the wound, often penetrating well into the more vital portions of 
the sapwood. It has been determined that the mycelium of wood- 
staining fungi is only prevented from entering the living sapwood 
by the high water content of the cells, as determining the presence 
of the necessary amount of oxygen demanded by the fungus. In all 
cases where the wood is exposed by wounds of any kind discoloration 
will take place. This wound rot. as it has been called in early 
stages of exposure, is not a decay, but a coloring of the wood through 
oxidation of the cell substances and the action of enzymes. The real 
decomposition of the woody cell is only brought about by fungi 
which act directly upon the cell wall. The early discoloration by 
exposure and staining fungi which do not act upon the wood is only 
a forerunner of the more serious condition of actual decay. The 
relation to fungous attack of the fire scars examined at Para was 
shown by the fact that the exposed wood was discolored by such 
fungi as Aspergillus, Penicillium, Hypoxylon. Xummularia. and 
other species. The wood was beginning to decay through the activi- 
61384°— 26 5 
