172 



Methods in Plant Histology 



in other places. The material is put in a dish of water, and after it 

 has settled the water is decanted. This is repeated until the water 

 will clear in about half an hour. The sediment is then treated with 

 an equal bulk of sulphuric acid, after which bichromate of potash 

 is added until all action ceases. After a couple of hours the acid is 



FIG. 36. Diatoms: diatomaceous earth from Cherryfield, Maine, showing the 

 great variety of forms usually found in such material ; photomicrograph from a prepara- 

 tion by Rev. E. L. Little. X400. 



washed out. To separate the diatoms, place the sediment in a glass 

 dish with water, and when the water becomes clear give the dish a 

 slight rotary motion. This will bring the diatoms to the top, when 

 they may be removed with a pipette and placed in alcohol. To 

 mount, place a number in distilled water, evaporate a few drops of 



