THE MICROBIOLOGY OF THE ATMOSPHERE 



100 ju, in diameter, carry most of the spores which are dispersed in this 

 fashion, and these droplets are massive enough to follow definite tra- 

 jectories without being truly airborne. 



o 



TT-rrT-v-TT- 



-7-rrrrrrrTTTT- 



r = 0-002l 



r=0-007 2" 



t- = o 



/ / / / ////// i / J I 

 t=0-0035" 



r=o-ooq" 



'7~r77~7-7-T7~. 



r = 00007" 



rTy-m^TTTrr- 

 \ =0-0055" 



t = 0-OI75" 



Fig. 4. — Splash from impact of water drop (5 mm. diameter) falling with 

 velocity of 440 cm. per sec. on a thin film of water (drawn from stills from ultra- 

 high-speed film made by Mr. E. D. Eyles at Kodak Research Laboratories, 

 Harrow). 



(vi) The splash-cup mechanism. This is a device, studied particularly 

 by Brodie (1951, 1957), which is widespread among lower as well as higher 

 plants, by which the energy of falling raindrops throws relatively large 

 bodies to distances of several feet. Examples are the peridioles of the 

 birds-nest fungi (Nidulariaceae), the gemmae of Polyporus conchatus, 

 and droplets bearing spermatozoids of the Bryophytes. However, the 

 projectiles scarcely become airborne, for they follow a definite trajectory. 



(vii) Hygroscopic movements of conidiophores, which may result in 

 detachment of spores during violent twisting, occur in a number of Fungi 

 Imperfecti and Phycomycetes. The effect depends on rapid changes in 

 atmospheric humidity and is often most marked in the morning hours. 



All active mechanisms for spore liberation depend on the fungus 

 having sufficient water-supply. The more ephemeral fruit-bodies develop 

 after rain and discharge spores for a short period only. More durable fungi 

 can be dried but will discharge spores again when re- wetted; others again 

 can draw on an extensive mycelium deep in the substratum and may be 

 almost independent of the weather. Distances of ejection vary and have 

 been compiled by Spector (1956, p. 153). 



(viii) Squirt-gun mechanism. This is found in many Ascomycetes in 

 which the ascus, which contains the ascospores, typically swells at maturity 



36 



