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Alg(?. The Algae are moisture-loving plants of very varied 

 form and texture, growing in both fresh and salt water, the 

 latter including the sea-weeds of our coasts, among which are 

 some of the largest representatives of this section. The fresh 

 water Algae contain some of the most minute of vegetable organ- 

 isms, requiring the help of a good microscope for their careful 

 determination. 



Lichens or Lichen-Fungi. The researches of Schwendener and 

 others have shewn that Lichens, formerly considered as a sepa- 

 rate tribe, must not only be included among the Fungi, but 

 must be regarded as a section of particular divisions of them 

 (Asco-,Hymeno-, and Gastevo-mycetes), and most modern students 

 of this tribe have adopted this system. 



The Lichen-Fungus consists of a Fungus and an Alga, living 

 and growing together in intimate connection. They are very 

 slow growing perennial plants, varying much in their form, 

 appearance, and texture, constituting a thallus, crust, or frond, 

 which frequently spreads horizontally upon soil, rocks, stones, 

 the trunks of living trees, and upon dead wood. They are 

 among the first plants which clothe the bare rocks and help to 

 form a humus for others of a higher organization to live and 

 flourish in. 



In the fruticose Lichens the thallus grows erect, branching 

 in a shrub-like manner. 



In the foliaceous Lichens the thallus is flattened into a leaf- 

 like expansion, and adheres to the substratum. 



The margin of the thallus is usually lobed. 



The thallus of the Crustaceous Lichens is usually indefinite 

 in outline, and can hardly be distinguished from the substratum, 

 the fructification alone being conspicuous. 



Many species of crustaceous Lichens grow on the highest 

 mountain peaks, and they contribute materially to the weather- 

 ing of the rocks, and formation of a vegetable soil. Those that 

 grow upon the trunks of living trees occur more especially upon 

 those which have a smooth surface, much more rarely on rough- 

 barked trees. Their growth is epiphytal, and they derive their 

 sustenance almost entirely from the atmosphere. They prefer 

 open exposed sites, and rarely grow in secluded shady places. 



