134 HEART-ROT CAUSED BY OTHER FUNGI] 
already dead, and thus save the tree, or it may be found 
desirable to remove the tree with as many roots as possible, 
and thereby save surrounding trees. 
These precautions are likely to repay the time spent on 
them, as the disease is not yet very common in Britain, 
and if taken in time epidemics may be prevented. But it is 
essential that all attacked portions of trees should be burnt, 
and not allowed to lie about in the forest, for the fungus 
fructifies with great regularity on all exposed surfaces of 
rotted wood. 
Poria vaporaria, (Pers.) Cooke. This fungus is reported as 
a wound parasite on various conifers both in Germany and 
the United States,’ and it probably occurs on the larch. 
But as it is probable that many species of fungi are in- 
cluded under this name, and as I have had no opportunity 
of studying the fungus on the larch, only a very brief account 
of the disease will be given. The information is derived 
from Hartig (1878), who found the rot which he attributed 
to this fungus several times on the Scots pine and once on 
the spruce. The rot so closely resembles that due to Poly- 
porus Schweimizit that the two may frequently have been 
confused. 
The fungus fructification is reswpinale, i.e. it does not 
form a bracket, but is confined to the under-side of the 
wood or tree on which it is growing, and does not extend 
beyond it. Its upper surface everywhere touches the tree 
and is hidden, and its lower surface is covered with small 
pores which bear the hymenial surface, as in the genus 
Polyporus. The two genera Poria and Polyporus are so 
closely allied that they were formerly included in one, 
and Hartig describes the fungus under the name of Polyporus 
vaporarius. The fructification is white, thin, and fragile. 
The trees which Hartig investigated were mostly 50 to 100 
years old. The rotted wood is at first light brown, but 
later it becomes dark brown, and at the same time shrinks 
so as to cause vertical and horizontal crevices, as in wood 
rotted by Polyporus Schweinitzii. Also the crevices become 
1-H. von Schrenk (1900). 
