427 



on its mycelium, and these are what the ants eat. Whenever the 

 mushroom is allowed to fruit it is necessary to clean off the garden 

 and start over again. 



Diseases. — There are not very many diseases of mushrooms other 

 than those due to animals. One, which is sometimes quite serious 

 among cultivated mushrooms, is called the mycogone disease. It is 

 due to one of the sac- fungus parasites, and causes the mushrooms to 

 become deformed and unfit for market. A similar disease attacks a 

 number of wild mushrooms. 



A very peculiar and interesting disease is found on Lentinus tigrinus 

 (page 428), a gill fungus which grows on rotten wood. It is due to 

 a parasitic mold which grows over the gill-surface to such an extent 

 that the gills, usually, are entirely hidden. So common are the dis- 

 eased forms of this mushroom that it was formerly thought to be a 

 perfectly normal condition. Recently, however, in some unpublished 

 studies by one of my students, Miss Esther Young, it has been shown 

 that it is a disease due to a species of mold belonging to the genus 

 Sporotrichum. 



Quite recently a disease of cultivated mushrooms due to a species 

 of bacterium has been reported. 



Fairy rings. — Certain mushrooms are often found growing in defi- 

 nite rings a few feet to twenty or more feet in diameter. These have 

 been known as fairy rings because long ago it was believed that when 

 the fairies danced around in circles during the night a mushroom 

 sprang up in each place where a fairy stepped. The cause of the rings 

 is that the mycelium which starts from a spore grows out in all direc- 

 tions forming a circular patch of mycelium but as it grows it produces 

 certain toxic substances which in time kill the older portions of the 

 plant. Each year the mycelium advances a little and produces a crop 

 of mushrooms so that the fairy ring increases in size from year to 

 year. Such fairy rings are commonly formed by Marasmius oread es, 

 Agaricus silvieola (page 473) and Lepiota Morgaui (page 459), and 

 sometimes by the giant puffball. 



Luminosity. — The phenomenon of luminositv in living beings has 

 been observed for a long time, though it is still not well understood. 

 The fireflies that flit about just after sundown of a summer's evening 

 are well known to every one. The light emitted bv them is of short 

 duration. Among the fungi there are certain species that emit light 

 continuously, under proper conditions, for days or weeks. Most con- 

 spicuous among these is Clitocyhc illudens (page 513), an orange- 

 colored mushroom that grows in clusters about old stumps. The gill- 

 surface of this mushroom is nearly always luminous, as can be ob- 



