OPEN-AIR CULTURE. 49 



in Indiana, Missouri, Kentiick}', and Arkansas — as well as in Vir- 

 ginia." The difficulty is to obtain caves within a convenient distance 

 from cities, for stable manure becomes expensive if it must be hauled 

 many miles or transported long distances by the carload. Again, 

 caves should be easy of access, since after each crop every vestige of 

 soil, manure, etc., of the preceding crop must be removed as a sani- 

 tary jjrecaution. This is especially necessary since there is much 

 Avaste space in most natural caves, and it becomes a very difficult or 

 expensive matter to fumigate. If the cave system is extensive, it 

 must also be possible to give it thorough ventilation. Many natural 

 caves are the courses of subterranean streams. The latter are l)y no 

 means objectional)le if there is no danger from overflow. In many 

 caves the stream has long since found a new channel and the cave 

 is dry. Seepage water, usually accompanied by continuous stalactite 

 and stalagmite formation, is undesirable. In some of the Eastern 

 States coalpits or coal mines may l>e important for mushroom [)ur- 

 poses. Where the coal mine is not too deep, or where perfect venti- 

 lation may be given, there is no reason why it is not entirely suitable 

 for mushroom growing. 



OPEN-AIR CULTURE. 



In some sections of England and France open-air culture of mush- 

 rooms in beds is practicable during the late autumn and winter 

 months, in which case the productive period may extend into the 

 spring. The difficulties in the wa}^ of open-air culture are not merely 

 those of maintaining a more or less uniform temjjerature, but also 

 of maintaining practically constant conditions of moisture. For 

 these reasons it is necessary to mulch the beds heavily with clean 

 straw. In some instances a light nudch of straw is permitted to 

 remain even during the period of production, for a rapid drying out 

 of the surface would be hazardous or fatal. It is better, perhaps, 

 to put the beds under some form of protection, such as an improvised 

 cold frame. 



In regions where the climatic changes are marked, open-air cul- 

 ture is ]:)robably not to be recommended during any season for com- 

 mercial purposes. It is probable that there are some areas in the 

 ITnited States in which open-air culture might be practiced with 

 profit. It has seemed that certain sections of California might be 

 favorable for this phase of the work. In the interest of experiments 



« The writer is indebted to Prof. C. F. Marbiit for the information that oaves 

 are to lie expected in the Sihirian limestone, which occurs particularly in the 

 extension of the Shenandoah Valley, in the hlucirrass resion of Kentucky, and 

 in tlie Ozark re.ij;ion of Missouri, and Arkansas; also in the Lower Carboniferous 

 limestoue, which extends into Indiana. Kentucky, Tennessee, and Missouri. 



