The Origin and Nature of Lichens 



An Alga-fungus company. The cut shows a 

 magnified portion of a lichen, Stereocaulon rantu- 

 losum, (Sw.). (h) colourless hyphae of a fungus en- 

 veloping, (g) filaments of a blue-green alga 

 Scytonema. 



power of absorbing great quantities of water and of resisting 

 alternate drying and wetting. 



The alga will perish if exposed to dry air, but when kept 

 moist is capable of taking elements from the air and 01 manufac- 

 turing them into plant-food 

 by means of little granules 

 of leaf-green it has in its 

 cells. 



In the alliance the fungus 

 is entirely dependent upon 

 the food manufactured by 

 the green alga and in return 

 keeps the sun's rays from 

 the alga and absorbs water 

 for its work. 



The Alga-fungus com- 

 pany, or lichen, is perhaps 

 one of the earliest instances 

 of division of labour, a 

 little community in which 

 one party manufactures and supplies food to the other which 

 serves as protector. 



The gray-green of a lichen is then due to the fact that a bright- 

 green plant is covered over by a translucent white plant, and the 

 brighter green of the wet lichen is due to the fact that the wet 

 strands of the fungus are rendered transparent by the absorbed 

 moisture, and permit the colour of the imbedded green to be seen. 



A magnified portion of a dissected lichen very much resembles 

 a tangle of fine white threads in which are scattered bits of green. 

 The white threads of the fungus creep around in search of 

 moisture and as a rule determine the shape the lichen is to be, 

 while the green cells or threads of the alga follow their protecting 

 fungus. However little moisture there may be in the surrounding 

 air, the fungus threads absorb it for their working companion, 

 and so the lichen can live in places too dry and parched for 

 other plants. 



"Strong in loveliness, they neither blanch in heat nor pine in 

 frost." 



On account of this dual nature it has been difficult to decide 

 where to place the lichens in the plant kingdom; to decide 



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