HOW TO KNOW THE SEAWEEDS 



Because of the tremendous 

 numbers of these tiny plants 

 in the sea, and of the per- 

 petual rain of their insoluble 

 silicious shells on the bot- 

 tom, great deposits accum- 

 ulate which may be hun- 

 dreds of feet deep. Some of 

 these deposits have been 

 raised above sea level and 

 form the beds of diatoma- 

 ceous earth such as occur 

 at Lompoc, California, and 

 are exploited commercially 

 for the making of fine scour- 

 ing compounds. 



On account of the very 

 small size of the phytoplank- 

 ton organisms, the high mag- 

 nifications needed for view- 

 ing them, and the special 

 methods required in collect- 

 ing, preserving and exam- 

 ining them, they do not lend 

 themselves readily to study 

 by the amateur or elemen- 

 tary student and will not be 

 treated further in this ac- 

 count. 



Fig. 3. Examples of two different forms of 

 plcnktonic diatoms. 



A. Asterolampra, a broad, flot, disc-like 

 form. B. Chaetoceras, a very small-bodied 

 form with long hair-like modifications of 

 the silicious frustule to aid in flotation. Both 

 X 200. 



