Another Life: Moss growth this year has been exceptional

In a rainy autumn, the moss grew thick as a rug on the concrete path to our door. A wavy white trail was worn down the middle by the postman, the SuperValu delivery man and a few fond and obliging friends in masks.

A bit ashamed, I took a spade to skim it off. Our daughter will come from Dublin at Christmas, the first time in almost a year, having quarantined for a fortnight with all her shopping done; we are hobbits enough already.

The moss growth has been quite exceptional, thriving in an atmosphere thickened hourly by the ocean’s exhalations. In dryer climes, it’s said that a boy scout lost in a wood could find north by seeing which side of the tree trunks the moss was on. Among our trees, he’d be walking round and round.

Many beautiful mosses found in the woods are worth kneeling down to admire, but this isn’t one of them. Its dark green fuzz has all the appeal of a worn and soggy rug.

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Ask Google which moss grows on concrete in Connacht and the answers would sooner discuss power hoses and other stuff to spray. Actually, a lot of mosses love concrete, with its mix of ground limestone and minerals. As wild plant life I might prefer to let it grow but the supermarket delivery man could have a skid with his big basket.

Another ground-dwelling substance objected to by many readers is the blue-green alga called nostoc. Its frequent substrate is limestone gravel, used throughout Ireland on paths, drives and flat roofs. In dry spells it remains flaccid and unremarked, but rain swells it into a bubbly and slippery imitation of seaweed.

Found globally, it was one of those unconsidered, pioneering cellular forms that helped create oxygen for later humans to breathe. An American scientist, Malcolm Potts, traced its original naming to the 15th-century Swiss physician Paracelsus.

Familiar with “the gelatinous colonies of the ubiquitous terrestrial cyanobacterium nostoc commune,” Potts proposed, Paracelsus played on fables of “excrement blown from the nostrils of some rheumatic planet.” In “nostoch” – first with an “h” – he melded German and Old English words for the nose.

“Star snot” and “star jelly” have been among English folk names for sudden and puzzling lumps of transparent goo, deposited on grass or twigs of trees and sometimes reported to Eye on Nature. Much imagined in the past as the stellar debris of meteor showers, it has been assessed by the British Natural History Museum as the eggless spawn of female frogs, coughed up in mid-air from the gullets of predatory herons.

Myxomycetes

Which brings us to other, more complex and colourful blobs that have figured in recent inquiries. They belong to the slime moulds, the myxomycetes, a group of strange and shape-shifting micro-organisms that hover at the biological boundary between plant and animal life.

Readers have variously described Mucilago crustacea as dollops of scrambled egg or something the dog might have vomited. The largest species in Ireland is the tapioca slime mould, Brefeldia maxima, which may cover a square metre of fallen leaves or sheath a branch in a conifer forest.

Closely related to amoebae, slime moulds develop a giant cell with multiple nuclei, called the plasmodium. This can move about to find food (bacteria and fungi on fallen leaves or rotting wood), if not at a pace that catches the human eye. A one-centimetre plasmodium can crawl about 10cm a day, the bigger ones even further.

One species of slime mould propels itself up tree trunks to feed on bracket fungi. A plasmodium can also have amazing shape-shifting powers, feeding itself into a crevice one end of a rotting log and expanding again at the other.

Japanese research with the species Physarum polycephalum has even demonstrated an apparent cellular “intelligence”. An experiment reported in 2000 showed the mould finding the shortest route through a laboratory maze. Studies since then have shown it making decisions and learning habitual behaviour.

Revelations on Physarum, said the Journal of Physics this year, “have triggered a surge of activity in numerous fields including physics, cell biology, genetics, behavioural ecology, computer science, natural computation and cognition among others, as well as philosophy of science and finally philosophy of mind”.

At the latest count, Ireland has 228 myxomycete species, 142 of them in Co Wicklow. Very many of these have been described by Dr Roland McHugh of the Dublin Institute of Technology, now an authority on their kind.

Given the many mysteries of slime moulds, it’s a nice match to find that Dr McHugh’s other lifelong obsession has been with James Joyce’s Finnegans Wake, to which he has published a widely praised book of annotations. Its line-by-line notes are now considered a great aid to exploring a notoriously shape-shifting book.