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.
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