THE AIR-SPORA OF ENCLOSED SPACES 



through the whole volume of air. With fruit-bodies of basidiomycetes 

 enclosed in chambers, Falck (1904) found that vertical tiers of horizontal 

 paper shelves became covered with spore deposit in a remarkably 

 uniform manner. By contrast, suspending the pileus of an agaric in a 

 small glass vessel often resulted in 'curious and fantastically' irregular 

 spore deposits on a piece of paper placed underneath. These were inter- 

 preted by Buller (1909) as due to the convection currents in the vessel 

 being of a velocity comparable with the terminal velocit}' of the spores. 

 The heat from a lamp was sufficient to alter a previously established 

 convection system. 



WARMER AIR 

 OUTSIDE 



COLDER AIR 

 OUTSIDE 



■7 



//////// 



y^ 



Fig. 23. — Diagram showing changes of circulation in a room 

 according to relative temperature of walls and of inside air. 



Even without any ventilation, air circulates in a room because of thermal 

 convection. Heating of air by rock surfaces in a mine may result in a 

 flow along an adit and up a shaft. Heating of glasshouses in sunlight also 

 leads to strong convection currents. 



Within a building the temperature of the air may be less changeable 

 than that outside, and this may lead to characteristic air-movement 

 patterns. Warmer walls will generate an up draught, colder walls a down 

 draught — each being balanced by opposite currents in the centre of the 

 room (Fig. 23) and often moving fast enough to counteract sedimentation 

 under the influence of gravity. Circulation of air within a house is complex, 

 but there is evidence of a fairly rapid exchange of air and of its suspended 

 spores throughout a house. C. M. Christensen (1950) experimented with 

 spores of Hormodendriim resimie, a mould that is peculiar for its ability 

 to grow on a coal-tar creosote medium, and therefore suitable for use as a 

 'marker' spore in dispersal experiments. Spores were liberated in a room 

 on the lowest floor of a house while all doors to the central hall-way were 

 left open. Within a few minutes, spores were found deposited on Petri 

 dishes in rooms communicating with the hall-way, but situated one, two 

 and three storeys higher. 



157 



