THE MICROBIOLOGY OF THE ATMOSPHERE 



TABLE XV 



NUMBER OF Lycopodiwil SPORES DEPOSITED ON UPPER AND LOWER SURFACES 

 OF HORIZONTAL TRAPS, Qp = 10^ SPORES LIBERATED NEAR GROUND-LEVEL 



(Gregory, unpublished) 



ELECTROSTATIC DEPOSITION 



The basidiospores of the cultivated mushroom and some other fungi 

 were shown by Duller (1909) to carry small electric charges when falling 

 in air. Little is known about the phenomenon, and its effect is pro- 

 bably negligible — except when the spore is within about a millimetre of 

 another body. The origin of the charge, its effect over very short dis- 

 tances, and its relation to the vertical potential gradient in the atmosphere, 

 which is said to average about 150 volts per metre, might repay future 

 investigation. 



Ingold (1957) suggested that in polyporous fungi with long and narrow, 

 vertical hymenial tubes, electrostatic forces may keep a basidiospore in 

 the middle of the tube, preventing deposition on the walls of the tube, 

 while the spore is slowly falling under gravity. Gregory (1957) showed that 

 basidiospores of Ganoderma applanatum usually carry a positive charge 

 when allowed to fall between two condenser plates which are charged 

 + and — 200 volts with respect to earth potential. In one test the average 

 deflection of the spores from the vertical was 12°, indicating a velocity 

 component towards the plate of 0-036 cm. per sec. in a field of 400 volts 

 per cm. 



The ascospores of Lophodermium [pinastri], the cause of pine leaf-cast 

 disease, are shot into the air from fruit-bodies on fallen pine-needles. 

 Rack (1959), using a potential difference of 75 volts in an apparatus 

 resembling ours, but without earthing the battery, claimed that immediately 

 on ejection from the ascus the spores carried a negative charge, but that, 



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