Why moss blows smoke rings

Science via Youtube today. Let’s start with some smoke rings.  They go an impressively long way—much further than a simple puff of smoke fired with the same force would:

So, why might a moss need to do the same thing?

It’s all about spores. Mosses spread by spores, a bit like microscopic seeds. For peat moss (Sphagnum), growing low on the ground in  bogs, the challenge is to catch the wind, getting its spores high enough that eddies in the air carry them away. It launches them, after building up 2–5 times atmospheric pressure behind them, but that by itself wouldn’t be enough: like a puff of smoke, the dust-like spores would quickly slow down, staying in the still air near the ground, and settling back to the ground. So they blow tiny smoke rings:

Could other plants use the same trick? Spores, pollen and the smallest seeds (such as those of orchids) could all potentially be ‘puffed’ like this. But most plants are high enough to catch the wind easily: the authors reckon it’s only about 10cm up in the bogs where peat moss lives. White mulberry, recently featured on QI as the ‘fastest thing in biology’, flings its pollen with a catapult mechanism (here’s the paper for subscribers) that couldn’t generate a ring vortex.

Maybe the best place to look would be fungi, some of which face a similar challenge to the peat moss when launching their spores. There are other ways to approach it, though. Take a look at these Pilobolus fungi, which use a ‘water pistol’ approach to launching spores (this paper is open access). Interestingly, the pressure they use to launch is similar to that in the moss.

Finally, to round off this post of Youtube science, let’s take a closer look at vortex rings (the technical name for smoke rings). They hold together by rolling through the air on the outside, while the inside’s moving forward faster. Here it is with ink in water:

Reference:

Whitaker, D., & Edwards, J. (2010). Sphagnum Moss Disperses Spores with Vortex Rings Science, 329 (5990), 406-406 DOI: 10.1126/science.1190179

How ivy hangs on

German scientists studying ivy (Hedera helix) have shown that its roots stick to things in four distinct steps:

1. Initial contact
2. Roots grow onto the surface, and lignify (get tougher).
3. Roots produce glue, which seems to react with the surface.
4. Tiny root hairs anchor the root to any minute crevices in the surface.

There’s quite a bit more about how the root hairs manage the final step. Their walls are structured so that, as a root hair dies and dries out, it coils up, catching on any irregularities and pulling the root in to the surface. If you’ve got access to the paper, have a look at the electron micrographs (unfortunately I can’t put them up here).

Sources:

English ivy’s climbing secrets revealed by scientists, BBC News, 28 May 2010

Melzer, B. et al. (2010) The attachment strategy of English ivy: a complex mechanism acting on several hierarchical levels, Interface, doi: 10.1098/​ rsif.2010.0140