214 ACOTYLEDONS ALG^E DIAGRAM 18. 



with time. They are generally of a grey colour, and sometimes 

 grow on the trunks of trees, and sometimes on walls and slates. 

 They require very little moisture. Some lichens appear like large 

 pendant filaments, which sometimes cover over fir-trees, and finally 

 destroy them. 



FAMILY OF ALGLffi. 



The family of Alga includes, firstly, the geeen filaments which 

 are found in stagnant waters, and secondly, the marine plants, 

 which are sometimes of a beautiful green, and sometimes of a brown 

 or red colour ; they cover the rocks, and it is a pleasant amusement 

 to collect and dry them. But they must be allowed to lie for 

 some time in fresh water, til) all the salt which they contain has 

 been washed out, or else they will not dry. 



The marine algae, or seaweeds, are useful for many purposes ; 

 firstly, they form an excellent manure when collected and spread 

 upon the land ; and, secondly, soda, iodine, and other chemicals 

 which are very useful in manufactures and medicine, are procured 

 from them. Soda is obtained by drying seaweeds in large heaps, 

 and then burning them and washing the ashes. The water 

 dissolves the soda, and, on evaporation, the soda is deposited in 

 crystals. 



Some species of seaweeds are used for food, such as the duke, 

 which is eaten raw or boiled, as a kind of vegetable, and the 



Carrageen Moss, which is used to make a kind of jelly. 



The longest of all known plants are seaweeds, and one species, 



which abounds in the Antarctic seas, is said to grow to the 



enormous length of 600 feet. 



