Larch bolete Suillus grevillei

 

These caramel-coloured larch boletes Suillus grevillei began to appear around the roots of larch trees in the Deerness valley this week. They are said to be edible, but those slimy caps are unappetising and it’s their biology rather than their flavour that I find interesting.

This is a mycorrhizal fungus, living in close association with larch tree roots, increasing their ability to absorb minerals from the soil in exchange for sugars from the tree that fuel the fungal growth. It exists for most of its life as a mass of hidden hyphal threads, thinner than human hairs, but early autumn provides a signal for a switch to reproductive growth, reorganising its weft of threads into these elegant toadstools.

When they first break through into the daylight the underside of the cap is covered with a veil that ruptures when the cap expands, exposing the spore-producing tissues.

In boletes the spores are produced inside thousands of fine tubes on the underside of the cap, that open via pores, to release the spores into the airstream.

To appreciate the beauty of the pores, and marvel at what finely-uned organisms toadstools can be, you really need to take a close look at their surface with a hand lens, and then …

… slice down through the cap with a razor blade, to expose the vertically-aligned tubes. In order for these to function effectively the microscopically-small spores lining the tubes must be able to freefall down and out through the pores, unimpeded, into the airstream. This depends on the toadstool’s finely tuned perception of earth’s gravitational pull, so that the tubes are always perfectly aligned with gravitational force; any deviation and the tubes would become clogged with spores that would stick to their walls. When toadstools are tilted, growth of the tubes (and gills of toadstools that have those) is quickly readjusted, to bring them back into vertical alignment.

So could you grow functional toadstools in outer space? For decades scientists have contemplated the potential for growing fungi in microgravity, to feed space travellers but its doubtful whether these beautiful, gravitationally-sensitive, aesthetically-pleasing toadstools would grow. There is, though, a SpaceX experiment in progress to see if toadstools will form, using oyster mushrooms (which have gills, not pores), in the microgravity environment of an orbiting space station.