QO PHYSIOLOGY. 



distinct from that of cither of the organisms forming the component parts. 

 This community of existence between two dilTerent organisms is called by 

 some midualism, or symbiosis, ^^'hile the alga inclosed within the meshes 

 of the fungus is not so free to develop, and probably does not attain the full 

 development which it would alone under favorable conditions, still it is 



Fig. S6. 



Section of fruit body or apothecium ()f lichen fpannt^lia), showing asci and spores 

 of the fungus. 



very likely that it is often preserved from destruction during very dry 

 periods, within the tough thallus, on the surface of bare rocks. 



