MUSHROOMS 409 
under its streets and properties, is the center of this great 
mushroom industry. Subterranean quarries near the city 
contain immense plantings, thousands of beds. In fact, 
the quarries are responsible for the tremendous develop- 
ment of this enterprise in France. The underground 
chambers are extremely variable in shape and dimen- 
sions. They may be 5 to 20 feet or more in height and 
width, and they may have entrances which are easily 
accessible, or it may be necessary to provide narrow 
openings above the quarries, with windlasses for the 
Fig. 145.—A modern commercial mushroom range at Kennett Square, Pa. Built of 
concrete and tile. Frostproof and fireproof. 
handling of manure and other materials. Ventilation is 
provided by means of special openings or ventilating 
devices of various descriptions. 
In England, caves, cellars and specially constructed 
houses are employed. In the United States, the bulk of 
the commercial crop is grown in special houses such as 
are shown in Figs. 147, 148 and 149. The majority of 
the American mushroom houses are cheap, wooden struc- 
tures, but in recent years more expensive buildings have 
been erected by experienced growers. Wood is unques- 
tionably the most common material used in the construc- 
tion of American mushroom houses, although many 
growers are employing the more durable materials, such 
as tile, brick and concrete, with air chambers in the walls. 
In most instances the houses are comparatively narrow, 
