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Orchids and Mycorhyza

Jeffrey Kirby ez043438 at dale.ucdavis.edu
Tue Apr 4 09:40:02 EST 1995

The answer to your question is yes. A lot of plants have symbiotic 
relationships with mycorrhizal fungus, usually a Rhizoctonia species (I 
think). Many orchids cannot germinate without this because the orchid 
seed has no endosperm or other food reserves. The fungus acts to break 
down complex nutrients in the surrounding media and then transport the 
results (such as carbohydrates and amino acids) into the plant, which can 
then grow. It's an endomycorrhizal fungus, not ecto (endo meaning the 
fungus is inside a cell of the orchid). Humans avoid this relationship by 
sowing orchid seeds on sterile medium that has all the nutrients they need 
in a form they can absorb. Some orchids have not been successfully raised 
this way (I'm pretty sure). Usually it's the terrestrial species that are 
hardest to raise without the fungus, and in nature, such species as 
Corallorrhiza species (which are leafless saphrophytes in North America) 
need the fungus all of their life to break down surrounding materials.

Most orchid books will give you an explanation like this, as will most 
general biology texts. Try:

Arditti, Joseph. 1992. _Fundamentals of Orchid Biology_. New York: John 
Wiley and Sons.


Jeffrey A. Kirby -- Jester of Xanadu -- jakirby at ucdavis.edu

I'd like to dedicate this .sig to all my fans out there, and tell you, 
"You're wrong. I am just a fruit."

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