[Plant-education] Pilobolus experiments

Barry Meatyard Barry.Meatyard at warwick.ac.uk
Wed Sep 28 03:59:54 EST 2005


Dear Christine (and all at Plant-Ed)
 
I used to use Pilobilus over 20 years ago (or that might be 30) - it's a brilliant fungus. In the Good Ol' Days before health and safety (during which period I'm sure we were all responsible for the deaths of hundreds of students) I used to collect fresh pony dung from a field near the campus and place it under a glass bell jar. Over a period of a couple of weeks it would go through a series of fungal succession - Phycometes, Ascomycetes and on to Basiodomycetes (or whatever modern nomenclature dictates) such as Coprinus. Pilobilus always appeared early in the sequence and, as I remember, without fail. The sporangiophores are strongly positively phototropic and bend towards the light and I arranged the illumination (daylight OK) so that they all pointed in the same direction. On the day of the class I would lay out a white paper 'firing range' and orientate the dung so that the sporangiophores were pointing 'down range'. The black sporangia were then easily identified against the white background when they were discharged and landed on the paper. Using such a set up it's possible to show that the range of the ballistic mechanism involved in sporangium discharge is up to 2m under still air conditions - I've lost all my notes so can't remember the record distance. We would simply observe the set up over the course of the class and mark where a sporangium landed with a coloured circle. In those days the actual mechanism was not easy to observe directly, although I suspect that now with the aid of macro digital cine photography one could observe a group of sporangiophores before, during and after the moment of discharge.
 
As a rider to this bit of fun I found out later there is an interesting link between Pilobilus and the horse lung worm Dictyocaulus. Most horse owners and casual observers will note that horses tend not to graze near their own dung, despite often more luxuriant growth of grass around a pile. Students could reflect on why this might be - possibly that those that had such a behavioural trait were less likely to pick up re-infections of parasites and their larvae lurking in the dung. Dictyocaulus appears to have solved the problem of increasing its chances of finding a new host by its larva (which occurs in the dung) being strongly negatively geotactic (gravitactic?) - it therefore crawls up anthing that happens to be sticking up in the air - including Pilobilus sporangiophores. A larva will thus climb up a sporangiophore and sit on the sporangium. It can then hitch a ride on a sporangium as a 'larval cannonball' and get fired beyond the close grazing limit that the horses informally impose on themselves. Thus there is an enhanced chance of the larva landing on grass that is likely to be grazed by the next unsuspecting equine host.
 
This must be published somewhere since I remember going to a symposium at the UK Institute of Biology in the mid 70s where I picked up this story - no doubt a lit search would turn up something.
 
Fascinating or what?? A tale of inter-relationship between 3 species (and possibly also the grass). Certainly the majority of students found this interesting if not amazing (some people are hard to please).
 
Although I've now moved out of teaching I still follow the threads on Plant-Ed. Great stuff and a point of contact with the real world.
 
Keep it up.
 
Best wishes to all,
 
Barry
 
Dr. Barry Meatyard 
Director, Achievement and Progression
National Academy for Gifted and Talented Youth 
University of Warwick 
Coventry 
CV4 7AL 
UK 
Tel: 44 (0) 24 76 574483  barry.meatyard at warwick.ac.uk 
www.nagty.ac.uk   

>>> "Christine Maxwell" <cmaxwell at trentu.ca> 09/28/05 12:06am >>>
Dear Plant-edders,
I have found it easy to culture this fungus following the discussions a short while ago.
While I can see that showing that the spores/sporangia land on only a lit area, I was wondering whether anyone had devised a method for actually watching the action or doing some sort of measurement?
Christine Maxwell

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