CHAPTEK IX 

 DIATOMS 



"T^vIATOMS constitute a group of microscopic 

 -*-^ plants found all over the world in most 

 waters fresh, brackish, or salt. They are 

 yellowish-brown in colour, and consist of a 

 single cell, free or adhering in chains or 

 planes. A coat of silica invests the plant. 

 This coat is composed of two valves, generally 

 alike, joined together by connecting girdles. 

 It is the opinion of some authorities that 

 the flinty structures are skeletons arranged 

 in symmetrical halves and joined at their 

 margins by an intermediate rim or hoop. 

 The valves are of various forms, and their 

 surfaces exhibit delicate markings. Many of 

 these united valves or skeletons are not 



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