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True saprophytes

Roger Whitehead rwhitehead at cix.compulink.co.uk
Mon May 6 05:31:43 EST 1996

This is an interesting question (to which I have no direct answer, I 
hasten to say!).

In northern Europe, we have a relative of the Indian Pipe called Yellow 
Bird's-Nest (Monotremata hypocrites). It is associated with a Boletus fungus 
that is in turn microrrhyzal on Pines. The sequence seems to be that the 
fungus and the tree swap phosphorus and sugars, and the dastardly Bird's-Nest 
helps itself to both from the fungus. Clearly, it is a parasite on the fungus 
and, as you say, an epiparasite on the tree.

In the case of certain orchids, such as the Bird's-Nest Orchid (Neottia 
nidus-avis), they are simply parasites on the fungus in their roots. That 
fungus (Rhizocotonia) is not parasitic on anything else, and lives off 
decaying vegatable matter (fallen Beech leaves in this case), breaking it 
down by enzymatic action.

However, things are not that simple. The boot was on the other foot at 
first. When the orchid seed was first penetrated by the fungus, it was the 
latter doing the parasitizing. Thereafter, plant and fungus have been 
engaged in a constant battle as to which is dominant. This is nothing like 
the cosy image of symbiosis that we are usually given, and more like the 
Hundred-Years War!

The other point arising from your question is the notion of the autotrophic 
plant. Mycorrhizal and bacterial associations are so common among trees and 
perennial herbs that one might justifiably wonder how many plants, other than 
annuals, are truly completely autotrophic. Is this a convenient label that. 
like many others, conceals a more complex truth? 


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Roger Whitehead,
14 Amy Road, Oxted, Surrey RH8 0PX, England
Tel: +44 (0)1883 713074; Fax: +44 (0)1883 716793

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