Marvels of the Universe 



391 



DIATOMS : WHAT ARE THEY ? 



BY E. T- SPITTA. F.R.M.S. 



Diatoms, or Brittleworts. are minute algae. But what does that mean ? Plants belonging to the class 

 algae grow in water, whether salt or fresh : seaweeds are algse. .\11 of this group, speaking popularly, 

 are separated into three grand divisions : olive-coloured, red-coloured and green-coloured. One of 





Pholo by] 



A GROUP OF DIATOMS. 



[-1. E. Smitli. 



Each of these microscopic plants, in spite of its minuteness, is delicately sculptured, each species with its own special 

 pattern. They are here shown about sixty times larger than the actual size. Several of them will be found, much more highly 

 magnified, on other pages. 



the sub-divisions of the green-coloured is peculiar in that its members all possess a flint-formed base, 

 which supports what is oft-times called the fleshy exterior or envelope. These are Diatoms. So 

 hard is this flinty matter, that if any Diatoms are placed on the tip of a knife and held in the flame 

 of a spirit-lamp to burn off their envelopes, the pure flint framework remains perfectly intact ; in 



