MASS AND MOMENTUM-TRANSFER ON THE SMALL-SCALE - HOW DO MUSHROOMS SHED THEIR SPORES

被引:31
作者
TURNER, JCR [1 ]
WEBSTER, J [1 ]
机构
[1] UNIV EXETER,DEPT BIOL SCI,EXETER EX4 4QF,ENGLAND
关键词
D O I
10.1016/0009-2509(91)85107-9
中图分类号
TQ [化学工业];
学科分类号
0817 ;
摘要
Many fungi can propagate by shedding spores. Ballistospore fungi fire their spores into the air. The mechanism for doing this involves the growth of a droplet on the base of the spore, close to its point of attachment to the fungus. This is probably achieved by the spore's excretion of a hygroscopic material which, when the surrounding humidity is high, causes water to condense on to it. The rate of growth of the droplet is shown to obey classical mass-transfer theory. The velocity of discharge of the spore can be deduced from the extent of sideways travel. Stokes' law holds for these particles both in discharge and in free fall. Spores are discharged at over 1 ms-1, and their sideways velocity is reduced to zero in about 1 mm. Such a velocity of discharge requires an acceleration of 25,000 g, and it is not obvious how such an acceleration to the required momentum can be produced. It is proposed that the droplet spreads rapidly over the spore. The drawing together of droplet and spore is resisted by the sterigma, or stalk, on which the spore is formed. This catapult action flings the spore away from the sterigma. Rough calculations show good agreement between the momentum required and the ability of surface tension to provide it. The application of the physical laws used in classical chemical engineering to a system as small as a discharging spore shows that scaling down can have as interesting consequences as scaling up. It may be a trism that nature is wonderful, but the fact that a spore can discharge itself so effectively using less than 0.2% of its mass should at least earn the respect of our present-day Space Agencies.
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页码:1145 / 1149
页数:5
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