STUDIES OF SPOBE-PLANTS 267 



249. Economic Relations of Mushrooms. Food Value. 

 The words " economic relations " will probably lead most read- 

 ers to think instantly of edible mushrooms. There are many 

 thousand species of the group to which the common mush- 

 rooms belong, and many of them are edible. The fact is 

 that thay have little value as human food, but they are deli- 

 cious as relishes. The wild forms are not commonly used 

 because of the difficulty of distinguishing with certainty 

 between edible and poisonous species. There is no safe 

 general rule; and botanists who have specially studied 

 mushrooms advise that no species should be eaten unless 

 identified by one who is competent. Especially should 

 people avoid mushrooms with a ring or cup at the base, for 

 this is one mark of the deadly Amanita, one of the most 

 poisonous plants known to science. Such books as Atkinson's 

 " Mushrooms " ; Marshall's " Mushroom Book " ; " Mush- 

 room Poisoning" a circular of the United States Depart- 

 ment of Agriculture; and Farlow's " Edible and Poisonous 

 Mushrooms " also issued by the United States Depart- 

 ment of Agriculture, give pictures and descriptions of many 

 species pronounced edible. But even with these books one 

 should be exceedingly cautious before deciding to eat a mush- 

 room which resembles those said to be poisonous. 



Effect on Timber. More important economically than 

 their food value is the destructive action of some mushrooms 

 on trees valuable for lumber. In sawing trees into lumber 

 the heart-wood is often found filled with white threads 

 (mycelium) which have so softened the wood as to make it 

 worthless. Hollow trees are usually due to such decay. The 

 mycelium seen in the wood is connected with a shelf-like 

 structure (often called shelf-mushroom or shelf-fungus) 

 on the bark of trees. In walking through woodland one can 

 easily find pieces of dead branches with small toadstools 

 attached, and if these be split open, the white thread-like 

 mycelium may be seen. These threads (hyphse) enter trees 



