CHLOROPHYCEAE 



219 



The silicious shells of diatoms are among the most beautiful objects 

 which could be examined with the microscope (Fig. 46). To obtain 

 perfectly clean mounts requires considerable time and patience, but 

 when the material is once cleaned, preparations may be made at any 

 time with very little trouble. Diatom enthusiasts have devised numer- 



'-' ^^'^ M 



Fig. 46. — Diatoms: diatomaceous earth from Cherryfield, Maine, a Pleistocene deposit, show- 

 ing the great variety of forms usually found in such material; photomicrograph by Miss Ethel 

 Thomas from a preparation by Rev. E. L. Little. X400. 



ous methods for cleaning them, and separating the various forms from 

 one another, but we shall give here only a few simple, practical meth- 

 ods. 



Dr. Wood's method of mounting frustules of living forms is easy 

 and effective: 



Material may be obtained by skimming off the brownish scum found on 

 ponds, by squeezing out water weeds, by scraping sticks and stones which are 



