What is scendesmus?

Scenedesmus is found everywhere as a constituent of the fresh-water plankton. It is more abundant in stagnant water. It often appears in considerable quantity in laboratory cultures, where it may be kept for years in a tightly closed glass jar without renewing the water, the lid being removed only when material is needed.

The form is so small that in living material little more than the general form can be distinguished. Excellent mounts are easily and quickly made. Smear a very thin layer of albumen fixative upon the slide, and add a drop of water containing the Scenedesmus. The drop may be inverted for 1 or 2 minutes over the fumes of 1 per cent osmic acid. No washing is necessary, and good mounts may be made without any fixing whatever. Allow the drop to dry completely. It is better to leave it for 24 hours before proceeding. The usual difficulty with this form, and with many others, is that the background stains and so makes the mounts untidy. The following method by Yamanouchi will produce beautiful preparations:

1. Dry on the slide, 24 hours. 2. 10 per cent alcohol over night to remove chlorophyll. 3. Safranin (alcoholic), 4 days. 4. Water, 5 minutes. 5. Aqueous gentian-violet, 2 days. 6. Water, a few seconds. 7. Orange G, aqueous, 3 minutes. 8. 95 per cent alcohol, a few seconds. 9. Absolute alcohol, 1 minute. 10. Clove oil, until the stain is satisfactory. Different collections of Scenedesmus stain very differently, but the time in clove oil is likely to be long, even as long as 6 hours. 11. Xylol, 5 minutes. 12. Mount in balsam.

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