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foams are planning further their spores through a "Smoke ring"! International Week


Spores out in the wind with a vortex
A study reveals that some Sphagnum moss

project their spores like a cannon - the accelerating 32'000g - and operate a aerodynamic phenomenon that prevails at 15-20 cm, much higher than expected: the air friction would stop after a few millimeters! A capsule which contracts as it dries, a seal that grants the crucial moment, and a vortex ring - a bit like smoke rings (vortex) - allow spores to reach the layers of air above where wind can carry them further and ensure the dissemination effective and has allowed these foams through the upheavals of many millions of years.

Dissemination of spores ... a problem!

We know how the spread of spores is a problem for foam: the layer of air at ground level is almost immobile, even when it's windy. It feels good when lying in the grass one day kiss the wind decreases near the ground. For mosses that live in the first millimeters, send spores as high as possible for them to find a place off to develop them is decisive. Foams are the current descendants of those who had adaptations allowing them to continue to live elsewhere when their environment has ceased to be viable!

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Fig 1: The sporangium rises above the rest of the foam. [Img
• ] Source: F. Lombard
• For the genus Sphagnum (285 species), Whitaker, DL, & Edwards, J. (2010) published interesting figures ( Extracts intranet.pdf ) which show the extent of the problem. Spores (22 to 45 microns) fall at a speed 0.5 to 2cm / s: a slightly turbulent wind just have to keep them in the air. To achieve these carriers winds, turbulent (above 10 cm in height) must be released spores in height - is what allows the lance-shaped (see Figure 1) of many sporangia. But it does a cm - and the project gives off much more likely to spread, which is what the article discusses. Air is a major barrier for spores Because compared to our size decreases the surface only to the square and volume - hence their weight - reduces the cube, tiny objects are much more subject to air friction. The friction in the air is so huge for the spores, because it is linked to the surface (disproportionately large compared to the weight for us). Relative to our size it is as if the air was really tacky. Or, in other words, it is like trying to play football or tennis with balloons: even going at full speed, it slows down very quickly and fall gently. Physicists speak of low Reynolds number: the viscous forces are larger than those of inertia (McMahon, TA, et al., 1983)
• . Thus, the friction should limit the distance that can reach spores less than one cm. See fig 2. blue and green.
• Fig 2: A, B
• Fig 3: The sporangium narrows and compresses the air in the bottom of the sporangium
• C Distance traveled by the ballistic calculations in still air (blue and green) and the observed distance of the cloud points red triangles and width. D
• Video ultra-fast (20,000 fps) of the massive release of spores, which produces a vortex ring.
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img] Source: Whitaker, DL, & Edwards, J. (2010)
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An American physicist and a biologist Whitaker, DL, & Edwards, J. (2010) have joined forces to publish an article in Science

here that analyzes the case of Sphagnum fimbriatum

: predictions by the simple ballistic observations encounter and highlight the effect of a vortex. The sporangium

Fig 3A shrinks as it dries and compresses air in the lower part (Fig. 3B) at pressures of 200 to 500 kPa. In the same issue Johan L. van Leeuwen (2010) describes how the pressure finally blow the lid releasing spores (20.000 to 240.000) that propels air pressure, as in a (tiny) gun, with a release rate of 16 ± 7 ms -1

and an average height of 114 ± 9 mm. The acceleration is 32'00g. It is the spore!

(ok it is not terrible, but I could not pass up this opportunity to place ...)

To get an idea an acceleration of 2g is reached by sports cars and F1 fighter jets inflict some 6g their drivers, but supported by special combinations ... Spores isolated launched with an initial speed of 13 ms -1 not culminate theoretically only 2 to 7 mm in less than 0.5 ms. While researchers have observed (Fig. 4B right) in 5 ms, they travel a distance of more than 40 mm at the end of which they are still moving at 3 ms -1
Fig 4: Sporangia of Sphagnum fimbriatum
(B)
capsule

ball becomes cylindrical drying. The rupture of the membrane releases the spores and the pressure of air propels the spores as in a barrel. The jet of air spores and rolls up Into a turbulent vortex ring spores That Carries up to 15 to 20 cm. (C) Air pressure (above ambient) Rises NONLIN. [Img
] Source N. KEVITIYAGALA / SCIENCE The authors explain that the vortex caused by the massive release of spores - and air - changes the aerodynamic system and product a vortex - a vortex ring - (see Figure 5) that accompanies the movement of spores to heights much higher.
Videos of the steps in this release are available in the Supporting Online Material here Unique in plants? vortices are produced by the jellyfish and octopus for propulsion and the authors note that this is perhaps the first time we described for plants. Such dispersal facilitated by the vortex may explain in part the success of Sphagnum , who survived the emergence of plants Vascular. Let me note that in some ways the current foams have a relatively longer duration than the ferns, conifers and flowering plants. You could say so provocative that they are "more advanced" than the ferns or flowering plants ... Just to show that any attempt to see evolution as a straight line is inconsistent. Aerodynamics Pollen dispersal agree, but the concentration? The question of aerodynamics of pollen dispersal is aided in gymnosperms and angiosperms by tree size, but at the other end of the journey to the grain of pollen, raises the question of the opposite gamete encounter - especially the likelihood of this meeting. Especially as the micropyle seems hidden in the scales. Again (KJ Niklas 1987) shows (see Figure 6) that ensure the effective vortex pollen concentration just on the micropyle of the egg-like when you stir a cup of tea and sugar is concentrated at the bottom and the center of the cup. Or as food particles in the gills of mussels probably! One might wonder if the inventor of the bagless Dyson which operates similar eddies merely copy - or reinvent - what conifers are over millions of years ... [img intranet] and [img intranet]
Fig 6: Aerodynamics of pollination facilitates the meeting of gametes. Source: Niklas KJ (1987)
Again the hazards and selection have produced modifications to the limits and sometimes appear to exceed the laws of physics and probability. Sources
MacMahon, TA & Bonner, JT (1983). It size and life . Scientific American Books. 
Niklas K. J.. (1987). Aerodynamics of wind pollination. ^{Scientific American} July: 90-95. Trad : Pour la Science (1987) septembre  Extraits intranet.pdf van Leeuwen, J. L. (2010). Launched at 36,000g.Science, 329(5990), 395-396. doi: 10.1126/science.1193047 Whitaker, D. L., & Edwards, J. (2010). Sphagnum Moss Disperses Spores with Vortex Rings. Science, 329(5990), 406. doi : 10.1126/science.1190179   about the evolution of biology. To explore how we could keep alive the link between research and teaching.