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, 1 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 Schweinitzii that the two may frequently have been 

 confused. 



The fungus fructification is resupinate, 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). 



