8 



CIRCULAR 2 51, U. S. DEPARTMENT OF AGRICULTURE 



heritable differences in the color, form, and growth habits of these 

 so-called varieties which breed true from spores, and in all proba- 

 bility some of them will be considered distinct species when given 

 critical taxonomic consideration. 



STRUCTURES FOR RAISING MUSHROOMS 



Mushrooms can be grown in any structure in which the grower can 

 control ventilation, maintain a moderately high humidity, and a 

 range of temperatures between 55° and 65° F. Contrary to pop- 

 ular belief, sunlight is not harmful to mushrooms, and they are usu- 

 ally grown in windowless sheds and in caves simply because it is easier 

 and cheaper to control temperature and humidity in structures with- 

 out windows. Old barns are frequently used. Occasionally waste 

 space in greenhouses is planted to mushrooms. A successful grower 



Figure 7. — Mushroom-housp construction. (Letters are referred to in the text) 



near Chicago has been growing mushrooms in an old brewery for 

 more than a decade. Sandstone caves along the Mississippi River 

 near St. Paul, Minn., have been used by commercial mushroom 

 growers for more than 40 years. Along the Hudson River near 

 Albany, N. Y., mushrooms are grown extensively in the old ice 

 houses. Near Pittsburgh, Pa., they are grown in partly abandoned 

 mines, and near Akron, N. Y., abandoned limestone quarries have 

 been used for 30 3^ears. 



In the industry as a whole, however, the specially constructed 

 house has found most favor, and at least three-fourths of the mush- 

 room crop in the United States is grown in these houses. (Fig. 7.) 

 The principal advantages of the special mushroom house are: It 

 can be suitably located with relation to railroad facilities, markets, 

 and manure supply; ventilation, temperature, and humidity can be 

 easily controlled, the air temperature in the house being raised dur- 

 ing final fermentation and the moisture and temperature controlled 

 during the spawn run and the bearing period ; separate houses may 



