CHAPTER IV 



THE ORIGIN AND NATURE OF LICHENS 



STRANGE opinions were entertained in regard to the origin oi 

 lichens. The belief was general that they were spontaneously 

 generated. In them the philosopher found the origin of plant 

 life. "Spontaneously, inorganic stone became living plant!" 

 Dr. Hornschuch wrote in 1819, "Algae, lichens, and mosses may 

 develop without seed from decomposing water. The decom- 

 position of water induced by warmth and sunlight gives rise 

 to the common ancestral type of algae, lichens, and mosses. 

 This ancestral type is a vegetable infusorium known as 

 monas lens which, when acted upon by light and air, under- 

 goes an evolutionary transformation into algae, lichens, and 

 moss." 



Nees Von Esenbeck, in 1820, was wont to lead his pupils to 

 an old castle in order to demonstrate ad oculos, how the green 

 substance when occurring on rocks will develop into lichens. 



De Bary was the first author to hint at the true nature of 

 lichens (1866). His conception of the lichen as a dual organism 

 composed of a fungus and an alga, was upheld by the researches 

 of Schwendener and Bornet in 1868. 



Further investigation seems to prove that the lichen is not an 

 individual plant, but that it is the result of an alliance perhaps for 

 mutual benefit between two forms of plant life, an alga and a 

 fungus. The alga gives the green colour to the lichen and is a 

 relative of the simple plants which make damp stone or wood- 

 work green on the shady sides of streets and houses and trees. 

 The fungus is a relative of the toadstools and moulds. If one 

 look at a piece of white mouldy bread, or in the ground at the base 

 of a toadstool, one can see a true fungus plant which is simply a 

 network of fine white treads (hyphce) stealing their food instead of 

 manufacturing it for themselves. They have lost their leaf-green 

 granules, the tools with which plant-food is manufactured from 

 air and water and mineral salts, but they have acquired the 



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