Chlorophyceae 173 



the mixture on a cover-glass, which is then mounted on a slide in 

 balsam." 1 



Many scouring soaps and silver polishes contain large quantities 

 of fossil diatoms, and the diatomaceous earths are particularly rich. 

 Break up a small lump of such material and boil it in hydrochloric 

 acid. A test-tube is very convenient for this process. Let the 

 diatoms settle, pour off the acid, and then wash in water. As soon 

 as the diatoms settle, the water should be poured off. The washing 

 should be continued until the hydrochloric acid has been removed. 

 When the washing is complete, pour on a little absolute alcohol, and 

 after a few minutes pour off the alcohol and add equal parts of 

 turpentine and carbolic acid. The material will keep indefinitely in 

 this condition, and may be mounted in balsam at any time. In 

 making a mount, put a little of the material on a slide and allow it 

 to become dry, or nearly dry, and then add the balsam and cover. If 

 the balsam should be added too soon, the diatoms are likely to move 

 to the edge of the cover. 



To show the cell contents, diatoms must be fixed and stained. 

 If they are clinging to filamentous algae, the algae with the diatoms 

 attached should be put into chromo-acetic acid (24 hours) and then 

 washed in water for 24 hours. Stain in iron-haematoxylin and 

 proceed by the Venetian turpentine method. When ready for 

 mounting, the diatoms can be scraped off from the algae or other 

 substratum. Other stains may be used. 



When the material is in gelatinous masses it may be fixed in 

 chromo-acetic acid, with or without a little osmic acid, and imbedded 

 in paraffin. There will, of course, be some difficulty in cutting, 

 but the knife often breaks the frustules very cleanly, so that good 

 sections may be secured. It might be worth while to try a weak 

 solution of hvdrofluoric acid to dissolve the silicious shells. 



/ 



Desmids.--The desmids are unicellular, free-floating or sus- 

 pended algae. They are much more abundant in soft water than in 

 hard. Deep pools, quiet ponds, and quiet margins of small lakes are 

 good collecting-grounds. Collections of other fresh-water algae 



1 From a review of Dr. Wood's paper on " Diatoms," Journal of Applied Microscopy, 

 March, 1899. 



